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MG MGA - Installing new generator and control box


Hey all,

I have a new generator and control box ready to go into my '56 MGA as my ignition light was constantly staying on. My question is this: Since my car is still positive ground, can anyone offer assistance on the procedure(s) needed to get everything installed and polarized correctly? The new generator says NEG GROUND on the casing of it so I need to polarize it properly. I'll put my questions in numerical format so it'll be easier...

1. After the new generator and control box are installed, do I just reconnect the battery the same way it's always been (still going to keep the car positive ground)?

2. Do I need to polarize the generator through the control box or do I do it directly at the generator?

..Sorry for all the questions, if someone would be willing to give me a literal "step by step" for doing this, it would be greatly appreciated, as electricals are not my strong suit for sure.

Thanks!
Aaron
Aaron Greenberg

Aaron, first of all sort out any polarity concious items on your car; usually not many on an MGA, radio is an obvious one, and electronic fuel pump or fuel pump with a diode across the points. Re wire your battery so that the negative is earth, this usually requires changing the earth and live terminals over as the pos and neg battery posts are different sizes. Then you "flash" (just touch the wire on to the terminal briefly, there will be a moderate spark) the field coil (small terminal) on the generator with the now positive battery live wire, and away you go. Finally, you will need to reverse your HT coil to get the best spark, so if you have an original coil, connect the SW terminal to the points and the CB terminal to the ignition switch wire, if you have a "modern" coil its simple, + goes to the switch wire and - goes to the ponts. Should be a piece of cake! Regards, Lindsay.
P.S. I think Barney Gaylord has a more comprehensive note on this subject on his site.
Lindsay Sampford

Aaron, its me again, if you want to keep +ve earth, forget everything I said and just flash the field coil on your generator!
Lindsay Sampford


Hi Lindsay,

Thank you for the quick reply. New problem, I'll start from the beginning....

A.) Went to start car a few weeks ago, battery was dead. I figured this was because of the constant ignition light yet I had driven the car a little but I guess I finally ran the battery down.

B.) Ok, no big deal. Unhook the terminals and charge the battery.

C.) Whilst battery is charging, I begin to get inquisitive about the MGA's electrical system so I have a poke around the control box, etc...to see how difficult it will be to change it. Doesn't look like a big deal but I notice that my old one uses the screw terminals and the new one I got has spade terminal connectors. Whoops! Looks like maybe they sent me an MGB unit? Anyhow, new control box and generator still sitting in their respective boxes.

D.) When charger indicates battery is full, I reconnect the terminals and when I go to put the key on and no ignition light at all! Weird thing is that if I pull the headlamp knob, the ignition light comes on (?????). I did fiddle with some of the wires at the control box but I put them back on exactly as they came off.

E.) So I try to crank the engine, it cranks and cranks and cranks, I hear the fuel pump working, fuel gauge works, flashers work but still no ignition light and doesn't seem like I have a functioning ignition now for some reason....oh, and my headlamps don't seem to work. Parking lamps work and flashers, but no headlamps. Remember that when I switch on the headlamps, it causes the ignition lamp to glow now for some reason. Really odd..

F.) So now I'm scratching my head over this. My plan is to put the new generator on and get the right control box and put that in then polarize the generator correctly and see what we've got. But does anyone have any ideas as to why I now have these gremlins? One thing of mention: I did have the various instruments and switches out of the dash to clean and wax the paint on the dash, but I didn't (to my knowledge) disconnect anything inadvertently...or maybe I did??

Sorry for all this, hope I'm being clear.

Cheers,
Aaron
Aaron Greenberg

Aaron, have you reversed the ignition warning light with the main beam light (rev counter and speedo) one of them is insulated, I think it is the ignition warning light, but at the moment I can't think how this transposition would stop your lights from working. Another thing to check; do your sidelights go off or dim when you try to turn on the headlights? That would indicate a short to earth on the headlight circuit. I will have a look at the diagram and see if I can work it out. Lindsay.
Lindsay Sampford

I am certain that you have transposed the Ign and main beam warning lights in their respective instrument casings, but I can't see why your headlights would be affected by that. I would think that you have got other faults, probably caused by wires being knocked out or broken when you waxed your dash. Get behind there with a torch and see if there' anything adrift. Did everything work before you dismantled the dashboard? You may not need that new generator and regulator! Lindsay.
Lindsay Sampford


Lindsay,

Well, that's what I thought, was that I accidentally switched the two warning globes around but I'm pretty sure I didn't. However, if I did switch them, when I put the key on, the globe in the "main beam" jewel would glow, but it doesn't work either. Also, thinking I may have switched the lamps around, I pressed the floor dip switch a couple of times to see if the lamp would extinguish, but it stayed on no matter what, so something's definitely amiss there. I'll have a prod around under the fascia and see if I may have knocked something loose, wiring-wise, but I was pretty careful and didn't have any of the switches out, just the little chrome bezels were unscrewed and the knobs were taken off. I moved any switches I was working near back into their holes a little bit so I could detail around their openings, but I definitely didn't disconnect anything. I'll probably take a wiring diagram with me under the fascia so I can make sure everything's hooked up the correct way.

As for my control box mystery, I definitely did receive an incorrect one. I returned it today and ordered the correct unit with the set screw connectors so when it arrives I'll put that in along with the new generator.

I noticed that on one wiring diagram I found on the MGA Guru website, it shows a wire leading from the Ignition lamp to the control box, so I wonder if my control box is indeed faulty like I am thinking?

Ok, so last but not least...

So, with the battery disconnected, I will install the new generator (marked negative earth) and control box. Then I am to hook up the battery, still in positive earth config, as I'd like to keep it that way. Once the terminals are hooked up, all I have to do to polarise the generator for positive earth is to quickly short across the A and F terminals of the control box and I'm good to go, right?

Thank you so much for all of your help!

Cheers,
Aaron
Aaron Greenberg

Hi Aaron, simple bit first! Fit the new generator but dont connect the wiring. Take a piece of insulated wire capable of carrying 10 amps; the size of normal car wiring, and long enough to reach from the starter switch to the generator. Hold one end on the field terminal,the smaller of the two generator terminals. Carefully touch the other end briefly on the live starter switch terminal and you should see a spark as you connect and disconnect the wire. Only srip the minimum of insulation off the end of your "flashing" wire to reduce the risk of bridging the live starter terminal to earth.
The ignition lamp is effectively connected between the A1 and D terminals on the regulator when you turn the key, so if you connect a test meter or a test lamp between those two teminals you should see the full twelve volts unless there is a disconnection in the wiring to or inside the generator or the A terminal is not at battery voltage. If that bit is ok, then the fault lies with the wiring back to the lamp, the lamp bulb itself or the ignition switch (which is not likely as you say your fuel pump and flashers work when the ignition is turned on).
Pity I live thousands of miles away, I could sort this in minutes if I was there!
Lindsay Sampford

I've been thinking about this whilst walking the dogs! If the main beam light is on in both dip switch positions it is down to a bad headlamp earth. The main beam warning light will derive its battery supply via the headlamp bulb filaments when the switch is in the dip position, but not enough current will flow to light the headlamps in either switch position. So there's a theory for two of the faults. The fact that the engine doesn't start could be caused by dirty CB points. All three of these faults could be caused by the car being laid up for a few months allowing corrosion of the connectors and the points, but you say you had been driving it, was that recently? Lindsay.
Lindsay Sampford


Lindsay,

Yes I do wish you were here! Fancy a free trip to the USA? lol

Anyhow, when you refer to 'starter switch' you mean the starter solenoid mounted on the right inner fender well? It has two leads going to it and a button in the middle, correct?

Ok, got the bit down about polarizing the generator, although I've heard so many different methods my head is starting to spin. Suppose I install the new generator and control box and then hook the battery up as normal. What would happen if I just arced the A and F terminals on the control box? Wouldn't that have the same effect as going right to the generator Field terminal leaving the generator disconnected?

I was driving the car up until a few weeks ago when I went to get it out one Sunday and the battery was dead. I removed the leads and hooked up the charger and figured whilst the battery was charging it would be an ideal time to remove some of the instruments and switches so I could clean and wax the fascia panel. I was very careful to make note of any wiring I had to unhook or fiddle with and, unless I completely missed something (I'd go out and look right now but I'm 600 miles away in Philadelphia on business), I'm pretty sure everything was put back correctly. But when I get home I'll scour around in there and see if something is amiss.

I'm pretty sure that my fiddling with the control box might be the cause of the ignition lamp not functioning, as I note that it is powered through one of the terminals on the box and I was messing with the wiring. Will check that headlamp wiring though, as I'm not sure if the headlamps were even working in the first place as I just got the car last fall and have barely had time to drive it let alone fiddle with it at all.

Thanks again for all your help!!

Aaron
Aaron Greenberg

My suggestion would be to not change anything until you diagnose the problem. Sounds like you have wiring problems and you need to get that straightened out first. With a fully charged battery, the car should start and run fine even if the generator and control box are bad. You could put a new generator and control box on only to have them burn out.

The first thing is to make sure that you don't have the ignition lamp and high beam lamp swapped. This is extremely easy to check as the ignition lamp has two wires going to it and the high beam lamp has only one wire. I suspect they are swapped and Lindsay's idea about the bad ground in the headlamp circuit makes sense.

Next, you need to double check the wiring to the control box. Barney has a page with a diagram of just the charging circuit which shows the proper connection. http://www.mgaguru.com/mgtech/electric/circ_c.htm

After you get the control box wiring straighted out you need to get the car started. If it will turn over but still won't start you need to make sure you have voltage to the coil. With the ignition switch turned on, the white wire to the coil should have 12 volts on it. If you don't, you need to trace back to the ignition switch. If it has 12v on the white wire at the coil and the car still won't start you have a general starting problem. It could be anything from the coil, points, plugs, condenser, carbs, timing, etc.

After you get the car running you can check out the charging circuit by following the step by step instructions starting on the second page of this document. http://www.vintagemg.com/ArticlePDFs/Tech103.pdf
















Jeff Schultz

Aaron, I'll get my bags packed right away!...only joking, but I have been to Ohio before, a friend of mine lived in Dayton years ago and he invited me and my wife over so I could tune the carbs on his E Type Jag! As Jeff says, get the engine running and your lights working before you do anything with your generator and control box. As I said before, you may even find that you don't need to replace them, and if I were a betting man, I would put any amount of money on your swapping the main beam and ignition lamps; I've done it myself. The ignition warning lamp is the one with two wires going to it. Let us know what you find when you get home.
Lindsay Sampford


Thanks for the comments guys. I checked the wiring to the instruments and sure enough, I had accidentally switched the bulbs! So I do in fact have a working ignition lamp and I do have spark. Now, for some reason, my fuel pump isn't working. I checked and I have 11.3 volts at the fuel pump (it's an aftermarket Purolaor pump which is wired for positive ground) but it's not ticking so I guess it must have gone south out of the blue. Question: I found a new SU dual polarity fuel pump for about $110 but it states it's for an MGB. Will this pump work ok on my car or should I just find another aftermarket pump? As for using another aftermarket unit, will they all work on either polarity or do I need a specific unit?

Thanks all!

Aaron
Aaron Greenberg

Unless you are really concerned with originality, better off just going with another aftermarket pump. Barney has a list of ones that work on his site. http://www.mgaguru.com/mgtech/fuel/fp201.htm

Also, many of the aftermarket pumps are so quiet you can hardly hear them so you need to check carefully to make sure it really is broken.
Jeff Schultz

Jeff;

The pump on my car definitely made a distinct ticking much as the SU pump on my '67 B-GT does. Anyhow; I confirmed the pump is nixed by the fact that there's no fuel getting to the carbs. I had a peek at Moss' website and found their version of the aftermarket pump so I'll just pick one of those up and get it on the car next week.

Cheers;
Aaron
Aaron Greenberg

This thread was discussed between 05/06/2009 and 12/06/2009

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