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MG Midget and Sprite Technical - Ignition failure

Well this one has me flummoxed. This is on my A35 with warmed over 1293 A Plus, alternator and Powerspark.

Slowing down as if for a junction and the ignition just cuts dead - it's just as if you've turned everything off at the key. Try to restart and it doesn't fire up, but after furious switching off and on of the ignition the dash lights return and it fires up immediately.
Back home all continuity checks are good,but the flasher unit has overheated and no longer works correctly.I substitute another and make up an ignition bypass switch - taking a live feed directly to the fuse box. Go shopping, slow for a turn and the engine cuts out again. So I switch on the bypass switch but it still won't fire up. More turning of the ignition key and the dash comes alive again and it fires immediately. But the flasher unit is fried again.

So I've done more checks and can find nothing wrong. Pulled the distributor and it's all good, coil doesn't get hot, all connections are insulated, soldered and clean. But there must be something in decelerating, braking and indicating that triggers the failure. I can't replicate it at home, no fuses are being blown - and no electrical smells either. Could a bad alternator produce a power spike, fry the flasher unit and disable the ignition? I'm going to replace the coil,ignition switch and fusebox but I'm fast running out of ideas. Alternator produces 14.1 Volts at almost any engine speed - 13.9 V with flashers on.
f pollock

Fraser


Have you checked all the earth connections, including earth strap to engine as well as to battery? And is the flasher unit and switch circuit feed and earth fine?

Cheers
Mike
M Wood

Yes earth connections are sound - engine spins over very smartly, and all earths to IP in place. Switching to flasher all good - it's a bi metal one so no earth needed - other than via bulbs.
f pollock

Sorry, I'm not sure what you've bypassed, indicators or part? ignition switch but as it didn't work how about disconnecting the indicators all together to take them out of the equation on a test run somewhere quiet where you can get away without them or use hand signals. Don't worry about hand signalling being unknown or forgotten about as using electric indicators seems to be going out of practice too.

Have you got hazards too, I expect not but always best not to assume.

Ignoring the indicators would bring to mind faulty ignition switch or faulty Powerspark or faults with wiring to either.

A complete electrical outage could suggest battery connections/leads or ignition switch depending on what's being used.

As you slow for the turn are you braking too?

Nigel Atkins

Fergus

Frying the flasher unit would suggest that there is an intermittent short somewhere downstream in the indicator circuit, although I would expect the fuse to blow.
Dave O'Neill 2

So the question is...one issue or 2 seprate issues?

I cant imagine how loosing the indicators would cause the engine to die esp during brakikg which only uses electric to power the brake ligjr switch

My guess is you habe some wornout wire thats making slight contact to the metql chassis and shorting out the emgine and mayne the indicator wire is burnt through also... the forward braking motion is enough for the wore out wire to contact the metal of rhe frame

The other thought... it could be the accuspark ignition system...there natorise for having and devoloping bugs
1 Paper

Is there a problem in the fuse box, that would be my first place to check after the switch and wiring

Which side of the fuses are you taking your 'jumper' feed for the ignition from?

And check the battery connections, both terminals

Bad connections can result there from poor connections to the cables

They can look OK but have loosened off inside the connections

Bill sdgpM

The bypass was to avoid a possibly troublesome ignition switch - so by making an additional/substitute connection from battery direct to A3 on the fuse box would ensure power got through. This proved not to be the case, as initially it made no difference if it got switched on or not. The system was still dead.
No hazards fitted, but yes, it happens sub 30 MPH,when decelerating + braking and with the indicators on. I too expected the fuse to protect the flasher unit, but checking I see I've fitted 25A continuous to 50A, which might be the reason, so I'll try the recommended 35A one instead.
f pollock

It is of course possible that the two faults are coincidental rather than actually related. As Prop suggests.

I have mentioned this before but l had an electronic ignition failure that was intermittent and difficult to trace. It turned out to be a break in the wire between coil and unit, but the external insulation remained intact. But once warmed up the plastic insulation softened enough to sag and under movement (acceleration & braking) the wires inside were intermittently making and breaking contact.

When l stopped and the engine bay cooled for a few minutes the insulation stiffened up drawing the internal broken wires back together again so the fault didn't show up with a meter continuity check.
GuyW

Going from the fuse box to by pass the ignition switch does still allow the fuse box connection(s) to be faulty/intermittent.

Even the fuse box internal connections and fuses can have poor connections so are worth checking all. I replaced my fuse box last year and was disappointed to find the male connectors on the new fuse box weren't a snug fit to my new insulated 6.3mm spade connectors.

To eliminate the alternator you could perhaps make up a drive belt just to the water pump leaving out the alternator and provided your battery is fully changed and in good condition, and the connections and leads in good condition, then you could do a good few test drives just on battery power.

I don't know enough about electrics to discount the alternator but it wouldn't be my first port of call.

ETA: I've heard of someone else having the same problem as Guy where a wire was fine until it warmed up/ got hot.

Nigel Atkins

I assume they're related because each time the ignition fails I've fried a flasher unit. I'm on my 4th now in as many weeks, but have today included an additional inline fuse between A4 on the fuse box and P. The Lucas ones are expensive to replace. I'll start a forensic examination of all wiring tomorrow. The fuses and housings are clean and shiny, but will be replaced next week anyway.
f pollock

It may not be relevant in this case but modern made flasher units can be rubbish anyway, whether those in Lucas green boxes are any better I don't know.

A4 to P I don't know about, is A4 after a fuse in the fuse box and what is P (or I might be lacking in the knowledge in this area), a photo of your wiring diagram might help with resolving this on here.

From recent electric issues for me (at a neighbour's garage) I'd advised starting at the battery and following the circuit all the way checking at every juncture rather than starting with the most obvious points on even very reasonable assumption.

Good luck.
Nigel Atkins

Well I've just started the car with all fuses removed. I suppose that's right as ignition and headlights aren't fuse dependent. Once the float chambers empty it will conk out of course, and not restart.
f pollock

When you said in original post that "dash lights return" do you mean the ignition light wouldn't illuminate but eventually did again (after which it started)?
W Bretherton

Well spotted Bill. ;-)
GuyW

Can't be sure about the ignition light, but I think it's off. Fuel gauge reads zero certainly.
f pollock

Ah,l thought you meant the dashboard panel lights failed, possibly suggesting an earthing short in the (green?) feed behind the dash.
GuyW

It almost sounds as if the battery supply is failing, maybe because the terminal connector has gone open circuit temporarily. Next time it happens, check for 12v at the fuses.
W Bretherton

I still wonder if the battery cables at the connectors have gone open circuit at times

If the alternator's regulator is slow to react to changing demand it might send more than the 14.5v max voltage into the car if there's a momentary break in the power lead

This might fry electronic components like the flasher unit

(all of which is sheer speculation, I'd want a half hour with my meter before I made any serious diagnosis) ;-)
Bill sdgpM

I wouldnt put in a new flasher, just take it out and get rhe car running without issue, thwn add in the new flasher

The advantage it takes the flasjer out of play and if the car still dies then you know the issues are not related

Prop

1 Paper

Another common factor is an incline. Twice it's happened going slightly uphill,and twice going slightly downhill. I like the battery idea,but the posts are all clean and tight,and it can't move about so whatever it is would have to be internal. Although when you pull on the starter the engine spins furiously and the dash is still dead. Shortest recovery time was about 5 seconds and the longest about 5 minutes.
f pollock

So the main battery connection is ok. Next time it dies, check for 12v at the fuses (both sides). I still think there is an intermittent break in ignition supply somewhere. That doesn't, though, explain why the flasher unit is frying although a short on the lamp side of the flasher circuit wouldn't do a bimetal flasher any good I think.
W Bretherton

Does it have an electronic tach? You could try disconnecting / bypassing that.
GuyW

Could it be connections at the stater solenoid or solenoid itself?

The up and down hill perhaps suggests movement from when level so again connections, or hidden wire miss-connections, somewhere.

I've seen where wire connections look fine but when you strip back the insulation the wires are fuzzed up (sorry can't think of any let alone correct technical term).

Internally for the battery is doubtful but not impossible I'd have thought, the car starts easily so probably not low electrolyte and exposed fizzed up plates but still worth checking - and perhaps checking the battery leads just after the clamp are solid.

Rather than jumping from one point to another I'd start at the battery and work forward in a methodical way as this will reassure and possibly pick up or prevent other possible current or future issues as well as hopefully find your current problem(s).
Nigel Atkins

Where is your alternator connected to? Is it directly to the post on the starter switch, or do you still have the regulator box in-situ?
Dave O'Neill 2

I had a similar problem with the solenoid wires that Nigel mentioned - after my rebuild the car died - nothing and then goes for a bit and dies.
Turned out to be one of the large lucar connectors onto the solenoid feeding the fusebox.
Possibly if the alternator output wire if it goes to the solenoid goes open circuit the alt gives high volts ?

R.
richard b

Starter solenoid is new, and all connections bright and shiny, just checked. Live feed from there goes to a gutted regulator box where A, A1 and D are joined together,(with F and E negative) and from there to the alternator. I've started going through each connection starting at the battery. Everything looks pretty good so far - but once it disappears into the loom it becomes akin to an act of faith versus the Prince of Darkness.
f pollock

If there is a temporary open circuit between solenoid (I.e. battery) and regulator connection then it's possible the alternator output goes high for a short time thus potentially damaging the flasher unit (if operated) whilst losing the ignition supply at the same time (because the battery supply is lost and the alternator will subsequently give up as engine revs drop e.g. slowing down at a junction).

Therefore I'd be strongly suspecting the wire from solenoid to regulator and/or the connections at either end.
W Bretherton

Fergus,
I expect you've already checked but you want all bright shiny new connections to be secure, (clean and protected) I've had new spade connectors that open out and become loose and the male spades on a new fusebox not the best fit to new 6.3mm spades.

Also from experience I always suspect modern made parts newly fitted, the solenoid in this case.

You can get round the loom by bypassing it using the connections at either of it instead connecting in a made up wire with correct connections and an in-line fuse if your worried.

I have made up wires and a selection of connectors so that I can go (where appropriate) straight from the battery post(s) to the item or connection so that I know I have a solid clean supply to test with.

Until DaveO mentioned it I didn't think of a control box or its connections, the letter now make (a little) more "sence" to me.
Nigel Atkins

I had a Caterham on loan for a while an it developed a fault that caused it to cut out, turned out to be the main spades in the alternator had become loose and not connected together and that coupled with the way the wiring loom was made caused the fault. The 2 main spade connectors in the Lucar connector had been used as one wire in and one wire out of the connector rather than the 2 being connected so the connection in the alternator made the forward connection for the current so when the connection in the alternator failed it cut the main power. I hadn't seen them used like that before, always the 2 in the Lucar connector being connected together.
David Billington

Thanks for all the contributions. I never did find anything untoward but have to assume it was a poor connection/high resistance failure that set off a little chain reaction that one or two of you correctly observed. In the end I replaced the ignition switch, fuse box, alternator and coil, as well as making up a dedicated lead from battery direct to alternator. A bit of a scatter gun approach, but 3 trips later and everything seems to be working as it should be. Fingers crossed it's sorted.


f pollock

Plus , here's the Frog in it's new house.


f pollock

This thread was discussed between 13/08/2017 and 18/08/2017

MG Midget and Sprite Technical index

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