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MG Midget and Sprite Technical - Where is my current going?

I have had an issue with escaping electricity for a while though as I have a battery isolating switch it hasn't greatly concerned me. But today I thought I would investigate.

Using a multimeter I measured the current between the battery negative terminal and the car earth cable, with the battery negative disconnected. (actually, measuring current flow between the terminals of my isolating switch)

1. Everything switched off, all the fuses removed, coil terminal disconnected and nothing apparently working.
I still get a reading of 0.57 Amps.

Then, as above but adding each fuse back in, but only one fuse in for each measurement:
2. Fuse 4 (Permanant live purple feed to horns etc): no change. 0.57A
3. Fuse 3 (Switchd feed Green to indicators, heater fan etc.): No change 0.57A
4. Fuse 2 (red feed wires): Current increases to 1.87A
5. Fuse 1 (more red feed wires): Current increases to 1.32A

So, there is a backgound constant of 0.57A The only thing I can think of is a radio memory connection. I don't know if my radio has one, and I thought the draw might have been less than that.

The escape through the red wire feeds is more concering, but oddly, if I put both fuses back in I still get 1.87. I expected it to go up to 2.62A Is this a clue of some sort? What should I try next?

GuyW

I assume this is your Spridget with an alternator ?

Have you tried disconecting it and rechecking ?

R.
richard b

Yes Richard, it's the '71 car. It was one of the last of the dynamo cars although I converted to alternator some years ago. (don't tell Dr Davies) And no, I haven't tried the measurements with the alternator disconnected. I will put that on the list for tomorrow's testing.
GuyW

Guy,

'4. Fuse 2 (red feed wires): Current increases to 1.87A
5. Fuse 1 (more red feed wires): Current increases to 1.32A '

I presume the figure for test 5 is a typo at 1.32A because that represents a decrease on test 4 1.87A .
David Billington

No, not a mis type David. I am using only one fuse at a time. Draw through one circuit (2 red wires) was 1.87A as measured at the bat. negative to ground connection. Draw through the other fuse (2 different red wires) was 1.32A

I assume also that since I appeared to have a background loss of 0.57A the draw through those 2 circuits was 1.3A (1.87 - 0.57) and 0.75 (1.32 - 0.57) respectively.

The puzzle was that with both fuses in place I still only got 1.87 draw. I cannot see how that could be so will repeat that test tomorrow to check.

The problem of course is that all of the outputs from those two fuses are the same colour, so difficult to trace. Not impossible, just difficult!

GuyW

As it’s red wires the next thing I would check are the main light switch and the dreaded column stalk.

R.
richard b

Should have added headlights are on relays.
Odd thing is there seem to be at least 2, if not 3 separate leakages. Bit of a coincidence unless its just general damp in components from lack of use the past 3 months.
GuyW

In that case I suggest pulling the power leads from the relays and checking again for leakage.

R.
richard b

I have my wiring diagrams at A3 but now wish I had scanned them and put them on the AO plotter when I was still working !
I do find the Bristows book useful for circuits as he pulls out just the single item I.e wipers or lights etc and makes it much easier to follow the wires, removing all the unrelated stuff from the wiring diagrams.
richard b

I have also had a defective alternator drain a midget battery over night. Definitely unplug the alternator to see if it is draining the system.
Glenn Mallory

Yes, I will try the tests again with the alternator disconnected.

I doubt if disconnecting the power feed to the light relays will effect the discharge at those two fuses. They supply via the light switch, and column stalk then blue/ white and blue/ red to the relay signal side. Power to the relays is a new added brown which doesnt come from these reds at the fusebox. But I will try that idea anyway Richard.

Since all of the output wires from those two fuses are red, I think all I can do is list all the components from the wiring diagram with a red wire supply and then go through on the car disconnecting each, one at a time. There may be a single point - a bullet connector - at the top of the A post, which would disconnect all of the rear loom. That could narrow it down.
GuyW

This is strange as you wouldn't expect a parasitic drain on three different circuits. I'd put the ammeter across the fuses, in turn, with the fuses removed, to verify what current there is in each of those circuits. The alternator could be drawing battery current (due to a leaky diode), which wouldn't be passing through any fuse, as it connects directly to battery. Is the regulator box still in circuit?
Bill Bretherton

<<you wouldn't expect a parasitic drain on three different circuits>>

I agree Bill. But it may be that the underlying 0.57 Amp drain is accounted for by either a radio "memory" supply - though I would expect that to be much less than that. Or the suggestion made that it is to do with the alternator. (Original control box no longer fitted)

That still leaves two possible "red wire" drains through those two fuses. Its stopped raining now so I will go and take some more measurements.
GuyW

I don't think there's any reason that three different ccts shouldn't have parasitic drain. Unlikely maybe but still possible.
One thing you really need to eliminate is the starter motor. They are infamous for quietly and unobtrusively leaking juice. Easy to find out by disconnecting the permanent live from the solenoid and usually easy to fix.
Good idea to have something like a bit of hose or some duct tape ready to put on the cable terminal to prevent fireworks.
Greybeard

Guy,
I'm with as others have put about the testing.

Also, I don't think you're allowing for, er, can't think of the word, the cross contamination/crosstalk/shared leak(s) that could take you from 0.57A to 1.87A with any combination or permutation of leaks.

No doubt you're using a good old analogue test meter that has been tested for accuracy rather than a cheap digital multimeter that are little more than single use then dispose of.

If the car is wired, more or less allowing for additions, as per factory the good book will let you know which red wires are to which fuses.

Bear in mind the red fuses are linked one side.

Just for your info, my car is an early (UK) 1973 and that's when the alternators first came in AFAIK UK Sprites all had dynamos.

(ETA: just checked, alternators started Dec '72 build according to Terry Horler's book.)
Nigel Atkins

Just thought, how is your radio wired, where does it get its switched and permanent supply(s) from?
Nigel Atkins

Ok more tests for anyone still interested!

First test, a correction. The combination of leaks does measure 2.59 with both the fuses, 1 and 2 in place. (not 1.87 as I recorded yesterday). So it IS the sum of tbe two as one would expect!

Disconnecting the alternator makes no difference to any of the readings.

Removing light, fan and brake light switch relays and disconnecting their power feeds also has no effect on the readings.

Current measured across the fuse holders for fuses 1 and 2 (battery reconnected, obviously) confirms the net leakage in each case ( i.e. excludes the background loss of 0.57Amps)

I then tried unplugging the stalk switch at its multiplug. this reduces the losses as measured across the two fuse holders by 0.16 in each case. Puzzling. Its either so low a reduction as to not signify anything or maybe there is a bit of damp or tracking in the switch. Not enough to worry about, but it still leaves over 1amp of drain through the fuse 2 circuit and 1/2amp through fuse 1.
(Nigel, thanks for the reminder, but the fact that the supply to these two fuses is linked under the fusebox makes no difference in the way I am measuring these losses downstream of the link. Also I have checked with both my analogue and my digital meters, and they agree. So I continued with the digital as its easier to read )

Loom is fairly standard as apart from my added relays it follows the factory layout (as per Handbook) However that doesn't help identify which is which out of the four red wires that disappear into the loon at the fusebox.

Anyone know what a radio memory should take? Could that be the background 0.57A ?
GuyW

Guy,
have you checked the underside of the fusebox for damp, crud or anything that could link anything to anything else.

If you've got four red wires on two connectors at the fusebox, switch everything on and carefully disconnect one connector, note what goes off, reconnect and do the same with the other and you get more idea, perhaps not 50% but more than 0%.

Is your radio wired into your car lights to alter display for car light on or off.
Nigel Atkins

More checks.
Disconnecting starter- no difference.
Disconnecting radio - no change.

And Nigel, no I haven't removed and cleaned the fusebox but have done the checks directly between the incoming supply wire and each of the output wires, so bypassing the fusebox altogether. But I will try and narrow down what the pairs of reds supply as you suggest. Thanks.

It seems then that I have:
A background leakage of 0.57 A, independent of fusebox, alternator, starter, radio or any of the relays. (starter solenoid? ignition switch?)

B leak of c.1A through fuse 2 red wire circuits

C leak of c. 1/2A through fuse 1 red wire circuits.
GuyW

Guy,

Have you taken the starter solenoid out of circuit to test.

With that sort of current draw I would have though some heat would be generated.

Check the main light switch and its feed to the fuses RG wire - is a rocker or lever type - the rocker ones seem to be more problematic.

R.
richard b

570mA equates to around 6 or 7 watts being burned. A small bulb somewhere maybe? . . . is the boot internal lamp permanently 'on'? You haven't got a hidden audio amplifier permanently on standby?

The only course of action is to sequentially disconnect all known loads, reading any current changes each time - and leave the loads disconnected as you progress. Make a written note of each load that is disconnected.

A switch could have gone internally resistive when in the 'off' position. Again, sequentially disconnecting all loads in turn will reveal the problem.
J Thomson

Whilst below might not be exactly as yours is I think as threads get long a visual representation is often good.



Nigel Atkins

Yes Nigel, that's as mine is wired. Excepting that the white out is joined elsewhere rather than at the fuse terminal so there is only the one white feed.

I've not done any more investigation since my last post as I ran out of my daily allowance. Another session tomorrow.
GuyW

IF your wiring is unmolested then the red circuits feed the left and right sidelights and number plate lights.

I would check all the bulb holders for corrosion and good grounding.
Chris at Octarine Services

As Chris says, the four red wires go to the side lights. Two to the front and two to the rear. The number plate lights are connected to their respective rear lamps, left and right.

I wouldn't expect the issue to be downstream of the fuses. It will be upstream, as there shouldn't be any power on the red/green - therefore no drain - when the lights are switched off.
Dave O'Neill 2

Something else to check:-
If you still have the panel light switch connected, switch it off and see if that makes any difference to your readings.
It's possible that a bad earth on one of the instruments could be causing something else to try to earth through the panel lights, also through the red/green wire to the fusebox.
Dave O'Neill 2

Dave
Guy said he'd measured current across fuses, if I've understood it correctly, so it would appear to be leakage somewhere downstream (in addition to the 0.57A background leakage current).
Bill Bretherton

Bill,
In my understanding to get current down stream with all switched off something upstream must be failing ?
richard b

Richard, if it's basically the standard loom, one fuse is permanent live even with ignition off.
David Smith

Bill

The red wires are connected to the side lights, so they will obviously be earthing through the filaments. With the lights switched off, there should be no voltage on the red/green wire, therefore no current to flow. The problem must be upstream.
Dave O'Neill 2

The only permanently live fuse is no. 4
Dave O'Neill 2

Dave S, as Dave O’N has just posted the problem is current in the red wires only as I understand the condition.
richard b

Dave O
Guy said he measured current in fuses 1 and 2 i.e. the red wire ones that feed lights. I agree you wouldn't expect any voltage at these fuses with lights off so something strange is happening.
Bill Bretherton

With such confidence all test should be conducted with bare feet in a bucket of water each and tongue against metal railings. :)

Just because a switch appears to be in the off position doesn't mean electrickery can't be getting through or round it.

Some wiring can end up like knitting patterns, knit one, pearl one, I should be good with those as when I tried knitting rather than adding I deconstructed what was already there.
Nigel Atkins

I think its fixed!
I took the rear light covers off and wiggled the bulbs around although they were all working as they should when switched on. Even so, I took the bulbs out and gave everything a clean up including the earth wire attachment points and reconnected with dabs of that electro grease stuff.

Following comments that it must be an "upstream fault" I also removed and dismantled the dashboard lighting switch. It had black grease inside with what I think may have been flecks of brass or copper. Not sure, but there were shiny bits that caught the sunlight. Cleaned and reassembled I now get a 0.00 A reading at each of the places that previously showed current leakage. Fingers crossed that has stopped it but I am not yet quite fully convinced.
GuyW

Good news Guy. It did sound like some issue with the sidelight circuit. A partial short in the light switch might cause your problem imv. A lower current than normal through the bulbs (due to a partial short) wouldn't show as illumination. The background 0.57A still seems odd.
Bill Bretherton

Guy,
switch, link, red wires - more convinced(?) but time and testing to be certain is fine.

Given this level of your lack of certainty on this matter - how many electric wires go to your radio (not counting the arial, earth and speaker(s) wires)?
Nigel Atkins

Good news Guy, I would pull the main light switch and give that a clean as well - if its the rocker type I have dismantled and reassembled them in the past as I have had problems with intermittent contact.
richard b

The light switch is a single toggle switch; off, side; headlights. I had to bend the cover plate up a little to open it up but it clipped back together ok. It has a good positive action unlike the rocker type which often feel a bit slack. At least they were so on my other car.

My uncertainty about it at the moment is that I was just getting zero readings, including at the battery post where I previously seemed to get a background 0.57A. I am not sure that the "fixes" so far would have resolved that.
GuyW

Maybe the light switch also had a partial short to earth to cause the 0.57A current.
Bill Bretherton

Maybe. I don't really understand.

If it was the switch, why would I get different current losses through one fuse from the other, when the switch was supposed to be off anyway, and no lights were coming on. And no smoke anywhere either!
GuyW

Only as one possible answer, might be not apply in your case but, more crud one one connection or set of connection than another connection or set of connections - the fusebox connection(s), the sprung fuse holders, the link between them.

Red/green from switch goes to fuse 1 split with fuse 2, at least 9, no 15, connections there, might be more but I've stopped counting as my tea is ready (dinner for others).
Nigel Atkins

Guy,
I have a spare Light 3 position toggle switch As you noted which you can have - I can stick it in the post.

R.
richard b

The different readings between the two different fuses could be down to a high resistance in one or more of the light fittings, or bullet connectors.

So many connections, so many opportunities.
Dave O'Neill 2

Thanks for the offer, Richard., But not needed, the switch is fine.

If the 3 position switch was leaking a supply through and the rear light gittings were earthing differently, that could account for the variations. Anyway it's not important now as it's all working ok. Just a lock down by-product of it's unusual lack of use.
GuyW

My 1971 Midget has a light in the boot, my 1970 B does not. Both cars have door switches and over the years, these have developed faults due to dirt, grease and impact.

I would check the boot light switch and the door switches if the problem persists.
Glenn Mallory

Guy
I reckon you've fixed it by cleaning out the switch
The bulb holders wouldn't have been in the circuit unless current was getting past the switch
I had a guy once who had pulled his sticky electric window switches apart and lubed them up with anti seize grease which had small metal flakes as you describe, it was interesting to drive along in his car with any little bump making a random window operate, cleaned all the switches out and lubed with vas. and all was well
Sorry I hadn't remembered this till you mentioned the metalic dark lube in your switch
willy
William Revit

guy if this hasn't fixed it, anything on the horn circuit? -
I can't remember if your car is +ve earth but I think either way there's a length of heavy duty cable that's permanently live/earth depending on the way round, and that's probably not enough current to get the horn to sound, but a short somewhere might be your leak?
timmyk

This thread was discussed between 08/07/2020 and 11/07/2020

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