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Frazzled wires behind the dash

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HA HA, ha ha, b*ll*cks.

Went out for a lovely drive to a local pub yesterday early evening, enjoying the new alternator, narrow belt and electric fan. Had a good pint of landlord sitting in the sun. Empty lanes on the way back driving into the setting sun, then whoof - a load of smoke from under the dashboard. I impressed Hazel and myself by isolating the battery within about 5 seconds (even though the switch is deep in the footwell on her side) and having the fire extinguisher out in about another 10 (but I may be exaggerating). I didn't use the extinguisher as the smoke cleared. After checking as many things as I could see, I tentatively started it again and it seemed ok. A passing car enthusiast said he saw some smoke coming of the exhaust and as we had just been over a big pot hole he theorised it could have been a dollop of oil thrown onto the exhaust. I liked to think he might be right.

Just as I got home I noticed the indicator warning light was not working, so today I started doing a more detailed check under the dashboard. As I started wiggling wires underneath, pow, a spark and lots of smoke again. Isolator was off in nano-seconds this time and extinguisher already by my side.

On my back with my head somewhere it shouldn't naturally be I managed to see that the black earth wire from the indicator warning light went to the little knurled nut on the speedo back, and then on to a little post on the back of the ammeter bracket. This section was frazzled and broken - presumably the cause of it not working yesterday. The earth wire then continues behind the H frame somewhere and is frazzled.

From the passenger side I can see what looks like a frazzled wire going somewhere with other wires, but I can't be more specific than that at the moment.

From the pictures I can see a brown and brown/white wire going into the top of the ammeter (which is in accord with my wiring diagram), and another brown wire appears to go on the bottom of the ammeter, but is just about touching the little post the earth wire appears to be attached to. The nut on the post is lose, so it seems to me the pot hole yesterday and my subsequent wiggling things today may have caused a short. The other pic is from the passenger side where I think I can make out two frazzled wires (or could be the same one twice).

I suppose I am going to have to remove things to get better access to see what's going on, but I'd appreciated any initial thoughts on what may have happened. In particular I obviously can't see where the normal earthing points are from the wiring diagrams, and I don't know why there are 3 wires going to the ammeter (plus one that looks like it's for the ammeter light).

The great thing is of course that it happened not far from home, we got home, and the car and us are not burnt out, though it is slightly concerning that something like this can happen without blowing fuses or something. Thanks for any help.







Edited by Ali King
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Hi Ali

Thats the problem nothing much with TR's seems to be fused until its too late!

That said I suspect that the back earth wire has managed to short to the ammeter terminal. The jolt may well have been just enough to finish off rubbing through its insulation which was already nearly gone. The loose connection won't have helped.

I'd resign yourself to pulling the dash and having a close look at what's fried once the wrapping is removed from the affected loom as often other wires will have suffered damage locally and sometimes distant from the initial problem. After 60 years it might be time to think of replacing the loom.

For what its worth mine on examination mine had been on fire in around 3 places and will be replaced along with the addition of extra fusing and relays.


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Sounds like your diagnosis is spot on. The strap clamping the ammeter to the dash is pretty close to the terminals anyway, & if your strap was a bit loose it could easily move enough to touch either of the terminals. They are both at 12V so either one would cause a lot of current to flow if shorted to earth. If the strap it's self was not making particularly good contact to earth then the current would flow through the black earth wire to the nearest proper earth connection, & would frazzle it .


Edited by Lebro
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Update ...

I took the dash and crash pad out this morning and as suspected the live lead at the back of the ammeter was shorting to the earth connection. This is like a daisy chain earth between (on mine) the indicator warning lamp, speedo, ammeter and oil gauge. Most of this was frazzled. The bit between the ammeter and oil gauge actually goes back into the loom so I had to dismantle that but was pleased to see it come out again at the next junction. Therefore all wires that were next to the frazzled one for a few centimetres are now exposed and all look ok.

Now the laborious task of putting it all back together again. All a bit annoying as I planned to refurbish the dashboard and have a general tidy up under there later this year - still, I've now had a practice run.

The only other thing was an unattached Brown/Green wire and two potential vacant spades next to it - one on the ignition switch and one on the windscreen wiper knob. My TR4A diagram shows 2 +earth coming out the wiper control and I only have one (red/green) +earth - so I'm assuming that's where it goes. But there 3 empty spades on the switch - which one?



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