Vixen electrical issue - help please

Vixen electrical issue - help please

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Moto

Original Poster:

1,230 posts

252 months

Saturday 15th December 2018
quotequote all
Sitting outside the local Post Office yesterday with the car idling, suddenly the engine cut out and grey smoke filled the space behind the rev counter glass (inside the rev-counter only). Immediately turned ignition off, smoke cleared. Tried turning the engine over again, would not start and smoke re-filled the rev-counter.

Investigation shows no signs of any melted wires or other indicators of any problem apart from I had fitted an in-line fuse between the starter solenoid & dizzy. This had blown. I replaced the fuse and it immediately blew on turning engine over.

So (I am a numpty with electrics) does this indicate what the fault is ? Starter solenoid or coil as the obvious candidates but all the tests I can find for solenoid only test for working or not (engine turns over fine). I am presuming that the Accuspark electronic ignition unit in the dizzy will have been fried so I don't want to try a replacement coil until I can determine the cause as I don't want to fit a new Accuspark unit just to fry it again.

I am presuming the smoke in the rev-counter was caused by excessive voltage dumped down the wire from the coil + post to the rev counter. Could either the coil or solenoid fail in a way that dumps excessive voltage down this wire?

Thx

Moto

Dollyman1850

6,316 posts

249 months

Saturday 15th December 2018
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Check connections on back of ammeter

If you say it is when cranking then it could be a seized or partially seized starter drawing too much current.

Could also be a main battery earth failing and the car is earthing via another route.

N.


Edited by Dollyman1850 on Saturday 15th December 19:05

RCK974X

2,521 posts

148 months

Saturday 15th December 2018
quotequote all
A couple of things which might help.....

If you saw smoke, SOMETHING BURNED !! I say this to get you thinking ....

Chances are, there's something that's gone black, or if it's a wire, it WILL have a melted part somewhere, but it's not always obvious when it's behind the dash.

Did it smell that horrible almost fishy smell ? in that case, it probably is a wire that's melted somewhere .

Probably you have one of these.........

1) a 'short' somewhere (a live wire is touching something it shouldn't). This can be a wire which has broken, leaving an exposed end, or it could have the insulation split due to age. Yes, it CAN 'just happen'

2) something has failed or jammed and is drawing too much power.

as you describe what happened, in my opinion, it's probably a broken wire somewhere, and it's shorting out. Instruments etc. don't draw that much current normally.
but it could be, say, the heater motor (but it will probably smell first, before failing completely) or something else.

See if you can get upside down and shine a torch under the dash.....that would be my first action, and then see about taking dash off.

Penelope Stopit

11,209 posts

108 months

Saturday 15th December 2018
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There is an ignition supply that comes from the ignition switch, loops around the back of or loops in the rev counter and then runs through the bulkhead into the engine bay where it connects to the ballast resistor which terminates to the ignition coil and in your car also the electronic ignition

A short circuit anywhere along that supply after the rev counter will overheat/melt/burn the wire

In reading your post I am guessing that you have fused the cable that runs from the ballast resistor contact at the starter solenoid cap to the ballast resistor, this fuse is blowing because the short is still on the ignition supply I mention above. Every time you operate the starter, the ballast wire from its solenoid cap contact becomes live, shorts to earth and blows the fuse

You need to find the short and it may well be in the distributor if that is where the amplifier is fitted, if the short isn't in the distributor it will very likely be on the wiring harness in the engine bay

If you have run a cable from starter solenoid cap to coil/ballast resistor, it is woth checking it for a short before going any further

It is very important that you check all the way through the wiring loom because a short in the engine bay will very likely have burnt the wire inside the car behind the dashboard as well as in the engine loom, sometimes a bit of luck comes into this type of short and the loom escapes being damaged, the thing is the rev counter definitely felt it

I posted you the following diagram several months ago https://www.pistonheads.com/gassing/topic.asp?h=0&... perhaps you didn't see it


Found here - http://www.tvr.at/grafiken/prwirdia.jpg

Edited by Penelope Stopit on Saturday 15th December 21:52

Moto

Original Poster:

1,230 posts

252 months

Sunday 16th December 2018
quotequote all
Thx guys.

I don't have a ballast resistor though. The car has always run a non-ballasted coil with a live wire direct from the starter solenoid to the coil. I guess this may have been changed from standard by a previous owner.

I have shone a torch up behind the dash and followed the white wire from the rev counter through the bulkhead to the coil and the white & blue wire from the coil to the solenoid and no signs of damage.

During the week I'll take the rev counter out to check thoroughly and also check the ignition wire that loops across the back of the dash. Yes I did have a copy of your wiring diagram thanks - spent yesterday using it to get my head around what wires are what. Very useful thx.

By the sound of it I get the impression that this is most likely a wiring fault as nobody suggests a fault in the coil or solenoid could have caused it. Is that correct?

Moto

Penelope Stopit

11,209 posts

108 months

Sunday 16th December 2018
quotequote all
Moto said:
Thx guys.

I don't have a ballast resistor though. The car has always run a non-ballasted coil with a live wire direct from the starter solenoid to the coil. I guess this may have been changed from standard by a previous owner.

I have shone a torch up behind the dash and followed the white wire from the rev counter through the bulkhead to the coil and the white & blue wire from the coil to the solenoid and no signs of damage.

During the week I'll take the rev counter out to check thoroughly and also check the ignition wire that loops across the back of the dash. Yes I did have a copy of your wiring diagram thanks - spent yesterday using it to get my head around what wires are what. Very useful thx.

By the sound of it I get the impression that this is most likely a wiring fault as nobody suggests a fault in the coil or solenoid could have caused it. Is that correct?

Moto
There is the possibility that the fault is down to the rev counter

A short circuit ignition coil could cause the problem but they don't tend to go short circuit

There shouldn't be a wire from the solenoid to the coil, this wire when used is to bypass a ballast resistor when fitted

Are there two spade terminals on the solenoid cap, one for cranking and one for ballast bypass?

The chances of the ballast bypass contact shorting to earth or shorting to the motor contact are extremely slim, see below image, the ballast bypass contact is the small one in the middle. the contact can be tested but your circuit shouldn't be using it




You could disconnect the ignition coil supply that comes from the rev counter, disconnect the solenoid to coil wire that shouldn't be in use and then supply the ignition coil from the battery positive with a length of cable, crank the engine and see if it runs ok

The ignition coil supply cable loop can be seen at the back of the rev counter in this image, I don't know if your rev counter is the same


Edited by Penelope Stopit on Sunday 16th December 17:13

timelord

316 posts

282 months

Sunday 16th December 2018
quotequote all
You say you are running an Accuspark electronic ignition system, has the rev counter been modified for electronic ignition? Should only be using one sensing wire if it has, the rev counter in mine failed due to over voltage from a slave battery start, Geoff

Moto

Original Poster:

1,230 posts

252 months

Saturday 22nd December 2018
quotequote all
The tacho is out and there is a very strong 'burnt something' smell coming from inside, so I'm guessing an internal component is definitely deceased.

The good news is that all the wiring seems to be in good order.

Still unsure about the car cutting out suddenly. I can only assume that a voltage spike killed the Accuspark EI. They are very sensitive to this. Whether a tacho failure could cause this though ???

I'll send the tacho off for repair and see what diagnosis they offer.

Moto

Moto

Original Poster:

1,230 posts

252 months

Monday 24th December 2018
quotequote all
Decided to strip the tacho just to see for myself what damage had occurred.



You can clearly see the ignition loop wires wrapping twice through the toroid having been fried. So I'm presuming they must have shorted at that point due to deterioration of the wires sheath. I guess they're probably 45 ish years old.

It has also melted the one end of the winding wire.



Hopefully it can all be repaired.

Moto

Penelope Stopit

11,209 posts

108 months

Monday 24th December 2018
quotequote all
If you can't see where the wire has rubbed through on and shorted to metal inside the rev counter there is every chance that it hasn't shorted, if it hasn't shorted it has been overloaded by a short elsewhere

Moto

Original Poster:

1,230 posts

252 months

Monday 24th December 2018
quotequote all
Bugger. I was assuming that as the burnt wires were contained within the tacho, that indicated the point of the short.

Back to the drawing board. Oh well I've got time to fill whilst the tacho goes off for repair. Back to checking & re-checking of the loom & behind the dash.

Moto

RCK974X

2,521 posts

148 months

Tuesday 25th December 2018
quotequote all
You can do a cheap repair yourself first.....

That burnt wire is only a simple loop through the coil unit, and you can use a roughly similar piece of wire to repair it.

OK, you may not have the right ends, but it should work with anything (like replacement spades).

Also what you have there is an old style 'current pulse' trigger tacho, which often does not work right with modern electronic ignitions.

So if you are sending it away anyway, consider getting the innards changed for a 'voltage pulse' trigger circuit instead.
(yes you can keep original dial and needle and all the mechanics, you just get a new circuit board inside).

Even though the actual short is probably somewhere else, that wire was the 'weakest' piece (=> the loop means it would heat up first...), but do check it didn't catch
on the case of the tacho somewhere..... if not, then you've got more detective work ahead !

If you did have some kind of ignition amplifier /electronic ignition added, then that unit could have failed and presented as a short across the battery, although it would be unusual if it didn't also get very hot (so will be stained/marked).

Otherwise, favourite is still a wire (or a couple) which has rubbed/ broken insulation somewhere to cause the short.






Edited by RCK974X on Tuesday 25th December 02:17

Moto

Original Poster:

1,230 posts

252 months

Tuesday 25th December 2018
quotequote all
RCK974X said:
You can do a cheap repair yourself first.....

That burnt wire is only a simple loop through the coil unit, and you can use a roughly similar piece of wire to repair it.

OK, you may not have the right ends, but it should work with anything (like replacement spades).

Also what you have there is an old style 'current pulse' trigger tacho, which often does not work right with modern electronic ignitions.

So if you are sending it away anyway, consider getting the innards changed for a 'voltage pulse' trigger circuit instead.
(yes you can keep original dial and needle and all the mechanics, you just get a new circuit board inside).

Even though the actual short is probably somewhere else, that wire was the 'weakest' piece (=> the loop means it would heat up first...), but do check it didn't catch
on the case of the tacho somewhere..... if not, then you've got more detective work ahead !

If you did have some kind of ignition amplifier /electronic ignition added, then that unit could have failed and presented as a short across the battery, although it would be unusual if it didn't also get very hot (so will be stained/marked).

Otherwise, favourite is still a wire (or a couple) which has rubbed/ broken insulation somewhere to cause the short.

Edited by RCK974X on Tuesday 25th December 02:17
I was going to do as you suggest & replace the ignition wire myself until I noticed the winding wire end had also melted & broken. In the photo you can just make it out. I don't have the tools to attempt to repair such a fine wire and reattach it to the blue blob thing (I have no idea what it is).

Also as I'm unsure as to any other damage to capacitors / resistors etc it needs to be checked & tested.

Thx for the info about changing to a voltage pulse trigger circuit. I'll speak with Smiths repairer about that.


Cheers for all the advice guys, will update you when I've made progress. Have a very Merry Christmas Day. drink

Moto

timelord

316 posts

282 months

Tuesday 25th December 2018
quotequote all
There are small pcb's available to fit in the tacho to convert to single wire detection when using electronic ignition systems

RCK974X

2,521 posts

148 months

Tuesday 25th December 2018
quotequote all
Moto said:
I was going to do as you suggest & replace the ignition wire myself until I noticed the winding wire end had also melted & broken. In the photo you can just make it out. I don't have the tools to attempt to repair such a fine wire and reattach it to the blue blob thing (I have no idea what it is).

Also as I'm unsure as to any other damage to capacitors / resistors etc it needs to be checked & tested.

Thx for the info about changing to a voltage pulse trigger circuit. I'll speak with Smiths repairer about that.


Cheers for all the advice guys, will update you when I've made progress. Have a very Merry Christmas Day. drink

Moto
Ah...right - didn't spot that. Yes, need a delicate hand and a soldering iron for that fix.....
The blue blob is connected to a variable resistor (the Yellow slotted cap thing) which allows for calibration of the tacho.

Yep, Smiths guys should be able to substitute a voltage trigger circuit for you. No idea of the cost though....

Later units used a 'prefab' type postage stamp sized board with a little IC chip on it.



Penelope Stopit

11,209 posts

108 months

Wednesday 26th December 2018
quotequote all
Moto said:
Bugger. I was assuming that as the burnt wires were contained within the tacho, that indicated the point of the short.

Back to the drawing board. Oh well I've got time to fill whilst the tacho goes off for repair. Back to checking & re-checking of the loom & behind the dash.

Moto
Good luck in finding the short, if you don't find the short you are faced with the same thing happening again, if all else fails you could fuse the ignition supply before the tacho until the short raises it's ugly head and becomes a permanent one that is easier to trace

I never fuse coil supplies as I can't cope with the thought of a car stopping dead while being driven due to a poor connection at a fuse or a fuse hairline cracking, ...........if needs must.....

Moto

Original Poster:

1,230 posts

252 months

Saturday 26th January 2019
quotequote all
After many unsuccessful hours spent tracing the wires along the loom and behind the dash, I decided the time was right to completely rewire the car. It had been on my wish list for a while as the original wiring was not great and a major issue was inevitable at some point.

A quick call to a local chap and 2 weeks later the car is done. The only original wiring left is the aerial cable and the interior light wire behind the roof lining.

I've had a few mods - a cut out switch now replaces the cigar lighter, a manual over ride switch on the engine fan and a dash light to show when on, wiring taken to behind rear trim for a rain light incase ever required, fully fused for each consumer unit, dynamo replaced with an alternator (so voltage stabiliser also gone) and a push button starter solenoid mounted in the engine bay drivers side so I can easily crank the engine when working on it.

Oh, and the tacho repaired and modified for electronic ignition.

All in a tidy job.