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MG MGA - jump leads

A while ago, I, stupidly, left my lights on whilst on an overnight crossing to the Continent. Of course, my battery was completely dead when I tried to start it and only jump starting would work. Tried jump leads which did give enough charge through the system to make the ignition light glow, but not enough juice to turn the starter. Question is this,... how should I have attached the jump leads,.. as I did to only one of the batteries or perhaps the pos. end to one battery and the neg. end to the other. Would I have had a different result.

Am not planning on doing this again, but "just in case" would appreciate clarification.

Cheers,

Jason
Jason Ogelman

Hi Jason. Jumper cables need to be connected at each of the jumper cable ends: red always goes to the positive battery terminal, Black always goes to the negative battery terminal. DO NOT connect ANY battery cables to either car's frames! ONLY connect booster cable clamps to the battery terminals! The reason for this is possible differences in the automobile grounds. Most newer cars use a negative ground system. MGA's were originally positive ground, but many have been converted to use negative ground. If you get the booster cables hooked up incorrectly, due to improper grounding, serious damage to the electical systems on BOTH vehicles is very likely. By connecting the cables ONLY to the batteries, as described above, accidental electical problems can be largely avoided. If you have a car that uses 2 batteries, (like some unmodified MGA's) then the same rule as above applies. The red booster cable would go to the positive battery terminal on one battery, and to the negative terminal on the other battery. The 2 batteries will have another wire that connects the two batteries together. Booster cables SHOULD NOT be connected to either of these two terminals. Hope this helps. Glenn
Glenn

I disagree with the above advice. When jumping a car the last connection should alway be made to the frame, or other appropriat ground, on the car being jumped. 2 reasons #1 and most imporrtant is that when the last cable is hooked up it will always create a spark. If this spark is near a battery it can explode. If you have ever experianced the destructive affects of the explosion or the acid shower that accompanies it you to would never risk it again. #2 reason is to protect the elect systems of the cars. If you have made a mistake and the last connection made is to the frame of the dead car all you have is a short circuit that involves only the good battery the jumper cables and the ground strap of the dead car. If you make a mistake when hooking up to both terminals you then run the risk of burning out electrical components. In a modern car this could fry the computer, the altrnator or other components and cost big$$$. I run an auto repair shop and have seen the carnage. The last connection is ALWAYS made to the frame,away from the battery, on the car being jumped. Glenn I am sorry to contradict you but in the intrest of saftey please rethink you method. If you don't understand this post or diagree please contact me and I will go over any misunderstandings personally.
SAFETY fast Randy
R J Brown

I think that the easiest way to fit jump cables on a MGA is to fit them to the terminals of the starter switch.
However, you can only do this if you know if you have a positive or negative ground.
I suggest MGA owners mark their starter switch with a red + and a black -.

Mick
Mick Anderson

Sorry, I am not fully awake yet (morning here).
Just mark the starter switch terminal either red + or black -.
One jumper lead goes from the red of the spare battery to red on the switch or the black of the spare battery to black on the switch.
The other spare battery lead goes to the frame.

Mick
Mick Anderson

Hi Randy. I think perhaps you may have misunderstood my posting. I fully agree with you regarding the order the jumper connections should be made in. My point was and is, that neither the car boosting, or the car being boosted should use the car frames as an attachment point for ground cables. If one car is positive ground, and the other car is negative ground, and booster cables are hooked to the frame on both cars, the electrical systems on these vehicles will likely be damaged. This is why I recommend connecting booster cables ONLY to the battery terminals of both vehicles involved in the boosting process. I hope this makes better sense, and clarifies what I was trying to say. Cheers! GLenn
Glenn

Glenn you misunderstood, if the last of the four ends to be connected is hooked to the frame of the dead car there are 2 choices. #1 you did it right and all is ok. #2 the cables are wrong and you have created a circuit that goes through the jump cables,the ground strap on the car being jumped and the frame of the car. In ths case you can't hurt any other components because they are not in the circuit. Also if you arn't sure that you have it right you can brush the cable against a ground point, if it acys like a arc welder it is backwards.
No matter what precaution is used someone will hook it up backwards,especially when there is a mix of posative and negative ground. People are that way trust me I've seen it too many times.
In addition to the FACT that if done the way I suggest you cant damage either car the most IMPORTANT reason to make the last connection to the frame and away from the battery is so it CAN'T EXPOLDE the battery and blind or maim any one. There was a recent story on a local news channel folowing the the story of an Asain woman who had battery acid thrown on her face by a jealous lover. She required multiple skin grafts and then multiple plastic surgeries to appear not too bad. She was beautifull before and is now just not scary to look at. Please if this doesnt make sense please ask for clarification if you understood what I was trying the say you would agree. SAFETY for the car and especialy for you.

NEVER HOOK UP ALL 4 ENDS TO THE BATTERIES IT COULD KILL YOU. if I havent covinced you yet I am failing in my explanation.
R J Brown

Hi Randy. I know hydrogen gas is very explosive, and I know that car batteries create hydrogen gas as they charge. Therefore, your point about car batteries possibly exploding IS well taken. In retrospect, since it would be possible that my boosting procedure might cause an explosion under certain circumstances, with safety in mind, I will withdraw my jumpering procedure above, as being potentially dangerous. (Even though I have been boosting vehicles this way without incident for well over 20 years) I will also change my own personal method of boosting vehicles to comply with your safer method. Having said that, then anyone who intends to jump start a vehicle needs to thoroughly understand positive VS negative grounds, and how to connect these two very different systems, so that an explosion is not possible, and that the possibility of electrical system damage is minimised. Frankly, I would still be very concerned about a positive ground and a negative ground car being incorrectly connected together, if the operators did not understand about the differences between positive and negative ground wiring systems. I believe that there is still a very good possibility of electrical system damage. If one touches the booster cable to ground, and it sparks "like an arc welder", you have probably just toasted the diodes in your alternator due to reversed polarity! Alternators and other solid state, polarity sensitive equipment, such as onboard computers, and stereo systems are very sensitive to reversed polarity, and can be EXTREMELY expensive to repair or replace! On the other hand, cars can be restored, sometimes human lives cannot! Thanks for taking the time to keep readers of this forum (myself included) safe! Cheers! GLenn
Glenn

Make sure the 2 cars aren't touching each other metal to metal, just hook them up positive to positive and negative to negative. Don't always believe red is positive. Look on the battery itself. And ground the last lead to a ground away from the battery, after checking for sparks. Luckily I have been some distance from batteries blowing up. One sounded like an M80 going off right outside the shop. The guy had just got in and turned the switch. No one hurt.
Tom

I understand the point about making the last connection away from the battery. Since the battery is connected to the chassis, electrically it makes no difference whether you connect to chassis or battery. Except that you're more likely to get it wrong.

Connecting +ve to +ve and -ve to -ve will always work. If you follow the modern procedure of connecting +ve to +ve and donor -ve to target chassis then that will short out the donor battery on a +ve earth car. It will be fine with a -ve earth one.

Jason, didn't you have a starting handle to hand?
Dan Smithers

When jumping our MGAs we first need to deterime polarity of the MGA. Is it posative earth as originally manufactured or has it been converted to negative ground.
We have two choises of where to hook the cables. We can hook the behind the seat in the area of the battery(s) or we can hook the at the starter switch attached to the frame near the starter.
There are advantages to both but like Mike Anderson posts above I preferr to attach at the switch.
The polarity of the car being jumped determines the order that the black or red cable is hooked up.
On a stock,posative earth,MGA the procedure would be to attach the "hot" ie not grounded cable first.
In order: 1st hook the black cable to the - battery terminal on the running car then hook the other end of the black cable to the battery side of the starter switch on the MGA. Then hook the red cable to the + terminal of the running car then lastly hook the last end of the red cable to an engine ground on the MGA.
If both cars are negative ground hook the red cable up first. 1st red to battery on running car 2nd red end to switch. Black cable second 3rd connetion to running battery 4th connection to engine ground.
If in jumping a modern car an error is made using the procedure of hooking the ground or black cable to an engine ground last you will get a large spark as you make the last connection, But because the only components that are then in circuit are 1 the Battery of donor car 2 the jumper cables #3 the the ground cables of the car being jumped you will not burn up computers or alternators. From a components point of view it is as if you hooked both cables to the bumper. Yes it creates s short circuit to the battry of the running car but the components of the car being jumped are not affected.
Having just re read Jasons original question. It sounds like you might have hooked up both cables to one of the two 6 volt batteries. Did you? If that was your question then yes that could have made the lights dim and not enouggh to start the car. it also sends double voltage to one battery and could cause it to be damaged or explode.
Another real common mistake I see all the time is people using too Cheap a set of cables. I have seen 10 or 12 gauge wire in poor quality cables. With wire that light not enough current car flow to start a car. 2 gauge multi strand wire is a minimum for 10 ft cables. Longer cables need to be thicker yet. Mine are 00 gauge (almost 1/4 in thick copper inside the insulator)
Protect yourself and your cars
Safty Fast Randy
R J Brown

Thanks for your replies. Why didn't I use the starter handle?... Good question.... at some time over the car's history, it was jacked up at an incorrect point on the front assembly and, with the weight of the car, bent the bit through which the starter handle would protrude and engage with the dog nut.

Any ideas on fixing this appreciated!

Randy, you're right, I did hook up the leads to just one battery and will, should I be faced with the same problem, hook up the neg to one battery and the pos to the other.

Thanks again.

Jason

Jason Ogelman

I always hook up inside the engine compartment. This has the advantage of not having any voltage drop from the battery cable, (keeps away from the battery, saves having to lift the hood out of the way and remove the cover), and gives me a good ground. It also is easier to do with shorter cables (though I have a 12 foot heavy duty tracator starter set from my days on the farm).

If you do it under the bonnet, you can also start the car and unhook again in no time at all, and keep clean hands. Try doing that at the battery.

I always insist on hooking cables up myself (I left my lights on outside the office all day once and had to call for a jump start as the starter handle was at home). This prevents others from assuming that all grounds are negative.

Only one tip doing it under the bonnet, make sure that you use the right side of the switch, and remember to let the fuel pump prime before starting pushing the pin on the starter switch.
dominic

Do you mean the front extension was bent? go to this web site. They do beautifull work. http://www.eclecticmotorworks.com/extprices.html
Jump the car from under the hood as Dominic describes. Dont hook up to the batteries at all.
Randy
R J Brown

Hi Randy. When you boost a car, you are (hopefully) ALWAYS connecting the batteries positive to positive, and negative to negative on each of the vehicles involved. This polarity issue needs to be STRICTLY adhered to, even when connecting the last booster cable via an automotive (chassis) ground. But what if someone gets the cables reversed? My ongoing concern is that even when using the vehicle's frame as the last ground connection, that it is entirely all too easy to reverse the battery polarity. (especially if cars of different ground polarities are involved) If extreme care is not taken when jumping a positive ground vehicle with a negative ground vehicle, (or vice versa) the end result will be reverse polarity through both car's electrical systems. (Remember the two vehicles are essentially having their batteries connected in parallel, either with correct polarity or (god forbid) reverse polarity) If vehicles are inadvertently connected with reverse polarity, this can and probably will cause serious damage, to one or both cars. I therefore still have to respectfully disagree with your idea that no damage can be done, even if the booster cables are incorrectly oriented. I have seen the end result of people's cars that were boosted with (accidental) reverse polarity, and the necessary repairs were not inexpensive. Cheers! Glenn
Glenn

Hi Folks. Perhaps this will help clear up any controversy about boosting vehicles,and also potential damage to vehicle electical systems by incorrect attachment of booster cables: This excerpt on how to boost vehicles was taken from a Ford Truck enthusiast website. Please note that it endorses Randy's safer method of connecting booster cables
Here is the URL: http://www.fordf150.net/howto/jumpstart.php

In regard to possible damage to vehicle electrical systems, please read point #2 fully.

1. On the vehicle with the dead battery, make sure everything is turned off (lights, ignition, etc.)
2. Check the batteries of both vehicles. Make sure you can clearly identify which is the positive (red) terminal and which is the negative (black) terminal. If you get these mixed up, you can fry both vehicle's electronics.
3. Make sure the vehicle with the good battery is running, and then connect the cables! This must be done in the following order:
- Connect one red clamp to the positive terminal of the dead battery
- Connect the other red clamp to the positive terminal of the good battery
- Connect the black clamp to the negative terminal of the good battery
- Connect the remaining black clamp to a ground of some sort on the vehicle with the dead battery. Do not connect it directly to the negative terminal. Examples of good grounds are: clean, metal surfaces (bolts or brackets). Note, you may get a small spark when you connect this final clamp.
4. Once they are connected properly, wait a minute or so (the good battery will slightly charge the bad battery). If the cables are connected correctly, the interior lights and other things on the bad car should work.
5. Start the car with the bad battery. If it doesn't start within 30 seconds, stop cranking and give it a break. If you crank too long, you can burn out your starter.
6. Once the car is going, disconnect the jumper cables in the reverse order:
- Remove the negative cable from the dead battery car
- Remove the negative cable from the good battery
- Remove the positive cable from the dead/weak battery
- Remove the positive cable from the good battery.
7. It's a good idea now to let the car with the weak battery run for a few minutes, and then do the following test. Turn the car off, and see if it can start on it's own. If it can, great, you're on your way. If not, you'll need to boost it again and have the charging system checked out (or do it yourself).
Glenn

Glenn we are each 1/2 right. Think on this
If the cables are reversed on the running car and correct on the dead car you can cause damage even if the last hook up is to the frame.
If the cables are correct on the running car and you hook the the dead car up backwards touching the black cable to an engine ground the short circuit created only involves ground cables and jumper cables. It wont hurt the dead cars alt computer etc.
The more we talk the more we think the more we learn even know it alls like me
Thanks Glenn,
Randy
R J Brown

It sounds as if there might be a place for a set of jumper cables with a mid-line breaker. I am always hesitant to create an underhood spark after an incident many years ago with a Hillman Minx that had a gas leak and went up in flames when testing a plug lead for spark. I also know someone hospitalized by an exploding battery.
John DeWolf

Hi Randy. I'm not trying to be difficult here, but I still believe, and firmly maintain that both vehicles would in all probability suffer severe damage from reversed polarity, even the "dead" car in your scenario. I think it matters not, which end of the battery cables is wrongly connected. Wrong polarity is wrong polarity, period. If either end of the booster cables is connected polarity incorrect, then the reverse polarity will damage both the vehicles involved. Think of your scenario in this way: The dead car is made to run on positive or negative ground, and it's electronic equipment is so wired. If you hook up the running car to the dead car, and accidentally hook the cables up backward (at either end), the Booster battery is now wired in parallel with the dead battery, except that the polarity IS NOW REVERSED. So essentially, the boosting vehicle is supply all power to the dead car's electrical system, but WITH REVERSED POLARITY! Even if polarity is reversed only for an instant, it is enough to fry every solid state device in both cars. I would hate to see someone suffer electrical system damage because of this issue, which is why I feel it is important to pursue and resolve the issue. My apologies if I seem pig headed. That is certainly not my intent. Cheers! Glenn
Glenn

I am not talking about reversed polarity I a talking about a direct short. If you hook up the ground cable last and have the other cable hooked to the wrong "ground" side of the battery you are not hooked in to the circuit of the dead car. Both jumpers hooked to the ground side won't hurt any thing but the things that are in circuit ie the running cars battery the jump cables and the ground straps in the car being jumped. Make a drawing of the circuit as described you will see it is so. That is one of the reasons to always hook up the ground cable to the dead car last.
Persistantly yours
Randy
R J Brown

Knowledge of your polarity apply to charging as well. One of my customer, using battery in back of his q van to start 18 hp kohler engine, put it on backward. It work. You can chage battery beckward. It gave me headache for week before I realised what he did.
martin

Hi Randy. I did make a diagram, and it still boils down to connecting a booster battery in parallel with the dead battery. Again, when you boost a vehicle, the vehicle being boosted has a dead battery. When you boost the vehicle with the dead battery, there are only 2 ways to connect the batteries with the booster cables. Either with correct polarity, or with reversed polarity. Since the boosting battery supplies power to the dead vehicle, it will supply either correct polarity to that vehicle's electrical system if the cables are correct, or reverse polarity, if the cables are incorrect. If polarity is reversed, (incorrect) you will damage the electronics in one and most likely both vehicles. I am talking about reversed polarity here, not a short circuit. I agree that a simple short circuit would do no damage. However, connecting booster cables backwards RESULTS IN REVERSE PPOLARITY, and WILL do damage. This additional excerpt was taken from the American Automobile Association website, and frankly, cannot be more clear about the dire consequences of hooking up booster cables backwards. (in other words, with reverse polarity) Note that the AAA also endorses your safer method of connecting the the booster cables, BUT again warns of electrical system damage if the booster cables are connected backwards !!!!! Please also note that this is the SECOND independent article I have posted that confirms the danger about reverse polarity indeed doing damage to one or both automotive electrical systems.

"CAUTION: Observe correct electrical system polarity when connecting jumper cables. The positive (+) cable must be connected to the positive (+) terminals of both batteries. The negative (-) cable must be connected to the negative (-) terminal of the booster battery and to a clean metal ground point on the engine of the disabled vehicle. Reversing the jumper cable connections will severely damage the electrical systems of one, or both, vehicles." Randy: I hope you heed the advice that I have posted from these independent websites! If you choose not to heed this advice with vehicles that you boost, then you do so at your own risk, and I wish you the very best of luck!
Also persistently yours, Glenn
Glenn

In the end, the target car will not suffer from incorrect connection. You will short circuit the donor battery.


for -ve earth to -ve earth

donor +ve .... target +ve
donor -ve .... target -ve

is electrically the same as
donor +ve .... target +ve
donor -ve .... target chassis (-ve)


for -ve earth to +ve earth
donor +ve .... target +ve
donor -ve .... target -ve

is completely different from
donor +ve .... target +ve
donor -ve .... target chassis (+ve)

In the last case, target +ve and target chassis are connected together resulting in a short circuit of the target battery.

I don't believe that there are any of the car components involved in this case apart from the battery of the donor car.

Dan Smithers

Glenn You are not reading what I wrote. Dan is correct. You have an opinion and are not examining it only defending it. All you wrote about reverse polarity is correct. What I am Saying is that if the running car is hooked up properly ther are 3 ways to hook up the cables not just the 2 you envision. 1 correct, 2 backwards and 3 the one you seem unable to recognise, the one where you are only 1/2 wrong. With the cables hooked properly to the running car and the + RED cable hooked to the - terminal of the battery of the dead car if you the hook up the black cable to an engine ground on the dead car you have created a direct short through the cables without risking damage to the eletrical system of the dead car. This is the second reason that you hook up the ground cable last and to the frame of the dead car, it protects you from damaging the electrical system of the dead car if the running car is hooked up properly. Can you see it yet? Don't respond untill you understand because if you disagree you still misunderstand.
IN addition if the groumd (Black) cable is alwasy hooked to the engine or frame of Both (negative ground ) cars no damage can be done to the Target car.
R J Brown

Hi Randy. My apologies. I did not see the third possibility via your written explanation(s) However, Dan's somewhat more visual approach clicked, and I now see and acknowledge the third possible situation, which would in fact result in a direct short to ground. Under this scenario, I would agree that no damage would be done to either vehicle's actual wiring harness, electronics, or any computer or audio equipment. However such a dead short could still do damage if not quickly disconnected) by melting the booster cables, or buckling the plates inside the donor car's battery, rendering it useless. However, I would think that such possibilities would be minimal. Again, my main concern was reversal of the booster cables, and therefore reverse polarity, which would fry delicate electronics. Cheers! Glenn
Glenn

I remember reading about a young person who designed a Foolproof set of jumper cables. Did a quick google search and found these. Just like I remember.

No fuss... No muss... Negative ground... positive ground..... batttery in the back.... starter switch in the front......last connection at the battery????

All addressed in this simple device. Just don't let the bumpers touch each other.



http://www.autosportcatalog.com/index.cfm/fa/p/pid/229/sc/2737


Chuck
Chuck Schaefer

One more thing, If you are jumping from or to a modern computer controlled auto, read it's operators manual. Some specifically state where to connect the jumper cables. Even done with the correct polarity, it is possible to get a slight reverse voltage (due to the high cranking currents) onto the computer and other electronics potentially damaging them. Your warranty may be voided if done incorrectly.

Always use the locations specified. Some give you a special positive terminal, others give you a special negative terminal and still others give you both.

Chuck
Chuck Schaefer

This thread was discussed between 08/09/2005 and 12/09/2005

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