Need help! Melted wires behind gauges under dash...

[hessel1974]

Hi,

I tried to crank my engine today with the fuel pump disconnected and lead from coil to distributor disconnected. It worked fine, untill i saw white smoke appear from under the dash and from behind the gauges.

it appears that some wires became so hot that the plastic around the copper melted causing the white smoke.

Funnily I cant find the wires which melted in the electrical diagram.

Mainly there is a blue/yellow wire which basically connects the fuel gauge, oil/temp gauge & speedometer which melted completely. all the other wires are pretty much ok. Also 2 brown negative wires (cigarrete lighter & glove box light) melted through.





Anybody has a clue what happened here? What is the blue/yellow wire for which connects the 3 gauges? can't find it in the haynes manual?

I had both batteries connected and also a battery charger.

thanks for your help!

[Fast Corners]

It looks like one of your light sockets failed. When they break, the assembly short circuits and fries the wires in that branch. The wiring may have been changed by a PO and that is possibly why you can not find them in the wiring diagram. What lights were the fried wires hooked up to?

[hessel1974]

to the oil pressure light, tank empy light and another one which i'm not sure what it does. It's also on the oil gauge and has a litte G on it.

But what about the earth wires on the cigarette lighter & glovebox light?

[dad911]

I've been meaning to do this: Dash Light Fuse Install

Now I think I'll move it to the top of the ToDo list!

[gsmith660]

Those aren't gauge light wires though! Those go to the indicator lights and would not be protected by that type of fuse install for the gauge lights.

[hessel1974]

hey guys,

can it be that these blue/yellow wires are the negative earth wires for all these lights? the wires whis are connected to the oil pressure switch and all the other devices which trigger these lamps to go on are ok. So I think the negative wires fried. What can be a reason for this to happen??

[304065]

Do yourself a big favor, go to the Pelican main page and download the wiring diagram for the 1971.

I actually had this EXACT same problem years ago, turned the key and smoke came out of the dash. What happens is over the years the insulation chafes until one day you end up with bare metal contact.

There is only one way to fix it, that is to painstakingly remove the old wires and splice in EXACT replacement wires with the same color and stripe. You can find the brass factory-type connectors with the rubber insulation at a number of sources such as ynzyesterdays parts, rhode island wiring or eagleday.

It took me the better part of a week to fabricate a new harness, it's not rocket science, just time consuming. You can then splice it into the car and connect everything back up.

Good luck!

[gsmith660]

Look at the wiring dia. here on pelican the blue/yellow wire goes to fuse #1 so it has juice I suspect if you dig you will find this wire shorted to the ground wire that is melted at the cig. lighter.

[hessel1974]

Thanks all!

I can confirm that these blue/yellow wires are ground! all these lights are connected from the clock to finally the light switch terminal 58a and finally to the chassis.

Same is for the cigarette lighter and glovebox light.

Can anybody tell me whether it makes sense that if these ground connections are not good, so not to bare metal anymore, these ground wires get too hot and melt? So if I restore or renew these ground connections and replace these wires in the loom, that should fix this? i'm not an electronics guy....

Thanks again!

[gsmith660]

They are not a ground look at the wiring diagram, they are probably grounded right now because they are melted to a ground wire, a ground would not go to a fuse that has 12 volts on it. If you look the transmitters that these wires corrospond to go to ground so the light has constant 12 volt on them and the transmitter closes to ground to complete the circuit and the light comes on.

[hessel1974]

Ok, after quite some studying yesterday night I found out that my blue/yellow wire should acyually be black/red according to the diagram.

So it is the 12 volt wire which starts at the starter and goes through the loom to all the clocks to provide 12V. So my guess is now that either it shortcircuited behind probably the tacho, which on itself fried some of the direct ground wires in the same loom.

I will be replacing this whole string of wires and are going to fuse them. Also, make a new ground connection under the dash to the body. And of course taking a good look next time I crank the engine


Thanks for all your help!!

[hessel1974]

Ok, another update.

I replaced all the melted wires today and bypassed the wire which melted in the wireloom.

I have narrowed it down to the wire which is fed from the 15 terminal on the ignition switch which provides 12 volt to the gauges. When I turn the key, this wire is getting terribly hot, so the start of the problem is this wire.

So the question is, why is this wire getting so hot when 12 volt is put on it? I'm not an expert, but I know you guys are out there to tell me what this can be.

Thanks!

[304065]

Well, the other end is shorted somehow. The wire goes from terminal 15 (look up DIN 72552 for a code as to what that means) to power the gauges. In my 911 it was a red wire with a spiral black stripe. Somehow, that is shorting out, either inside one of the gauges or somewhere on the metal. What terminals exactly is it connected to?

[hessel1974]

It starts at the 12V+ terminal of the tacho, then goes to the large combo instrument to the 3 lights (alternator, Oil pressure & hand brake)

Then it continues to the fuel tank gauge on 12V+ and lamp for light. This is where it ends.

Would it be a wise idea to plug it off the gauges one by one starting at the fuel tank gauge?

[hessel1974]

Ok, I got it!!! Someone put the 12v+ wire on an earth connector of the fuel tank gauge....... This shorted it all out. I had the switch on for 3 minutes and no wires became hot...

Any chance this all damaged any of the gauges???