My '71 914 sat for almost 15 years, until about two months ago when I was finally able to get it back to life.

Initially, all was well but about two weeks ago I began having starter troubles. Would turn key to accessory and all was normal, again over to start and the fuel pump would click on, lights would dim but no starter action. I was able to use a screwdriver to bridge the contacts on the starter solenoid, and the starter turned
over as normal. I also measured a full 12 volts at the yellow starter solenoid wire when the key was turned to start. Following the harness back I also verified 12 volts at the flat connector on the control board.

After reconnecting the flat connector to the control board, the starter magically began working again. Assumed a loose connection somewhere and was about to take it apart again when the harness went up. The black wire which connects the positive terminal on the coil to the control box seems to have been the source, and melted into the rest of the wires and the sheathing the set is wrapped in.

I had tugged on the harness and hooked my volt-meter back up to the yellow solenoid wire at the starter, hopped back into the car and turned the key to bump the starter and measure voltage when it happened. I assume it's due to something in the start circuit, but can't think of any way the power wire to the coil would itself be directly connected to the starter wire.

The black wire between the coil and control box seems to be the only one to have burnt out - the others all appear to be basically fine. I can only assume that somewhere in the bundle the outer sheath tore and allowed that wire to rub against a piece of metal, trouble is with the wire and sheathing melted I can't tell where that might have been.

Another alternative is that something in the control box has gone bad and created the short. Alternately, something which draws power through that wire via the control box has grounded out and was simply
of a larger gauge wire and didn't burn out as quickly. At this point I really don't know.

I'll pull the harness tonight or tomorrow, pull back the casing and see if I can spot anything. If that doesn't turn up anything I'll wire in a temporary replacement for the black wire and see what happens when I hook that up with the remaining good portion of the harness.

Any suggestions on what to look for?

Thanks,

Cole

Hi Cole...

Come on guys...any input is appreciated...

Geeze, Jeff, aren't you the wiring harness guru?

Cole, If by black wire, you mean the black with purple tracer that goes to the coil, I've had the same thing happen. It's the tach wire, and it either grounded out, or was on the wrong coil post (it goes the same place the green condenser wire goes to). I'm sure someone here has that harness (hi Jeff) or I can probably scrounge one if needed. Mark

It could be burnt all the way up to the tach.. (That'd be ugly)

It's probably not the black/purple wire to the tach. It's more likely the black or black/red wire to the coil + terminal. Both wires probably just look black now, as the purple and red tend to fade.

If it is the coil + wire, then current will flow through that if the points are closed. If the coil itself has shorted internally between the posts, you'll see a lot of current there. Try disconnecting all of the coil wires and measure the resistance across the two side terminals on the coil. It should be at least 0.5 ohm, and could be 3-4 ohms if the coil is internally ballasted. The other source of high current through this wire would be something shorting the coil + terminal itself to ground, like a loose wire someplace.

If it's the coil - wire, very little current should flow through that, since it's "powered" by the coil, so again, the coil itself would have to short out internally.

As it turns out, it's the black and purple wire - which was plugged into the negative terminal of the coil, along with the condenser - which shorted out. Have peeled back sections of the sheathing and it seems the rest of the wiring survived; this one was the only casualty.

So, what might cause that (tach?) wire to burn out in such spectacular style?
Is a short within the coil the likely culprit?
Given the pin photo, are all the wires in the black connector going to the right spots?
What's the next step?






Thanks!

Cole

If the condensor shorted, then that's another path straight to ground, as the condensor will conduct through the distributor body right to ground. Car doesn't run in this condition, as I'm sure you discovered. The coil may also be shorted internally, and that would mean you'd have a fair amount of current flowing from the battery, through the ignition switch, through the coil, through the condensor, to ground. This, however, should have caused the black/red (or black) wire to get pretty hot, too. The 25A fuse on the relay board also should have blown.

I don't know the internal tach circuit well enough to know how the power would flow through it to the coil, where it would again ground if the points are closed. If the tach wire itself shorted to power somewhere, that would cause all kinds of trouble, including possibly burning up your condensor. This short could happen on the relay board, or inside the wiring harness sheath.

What's that black wire with the insulated connector on it lead to? The one also attached to coil -. Is that a remade distributor wire? Those are normally green.

that's the tach wire......not the condensor wire at all......

it would have to be one hell of a current to melt the insulation off......

like a full 12V to ground scenerio......



b, who is clueless and stunned as to what happened

The wire between the dizzy and the coil is suppposed to trigger the firing of the coil.
A simple grounding device. And of course signal the tach.

to cook THAT wire would take some constant flow of Amps. Not your regular little triggering ground wire. I think somethings shorted and it's constant.

Like Lapuali said, First check for internal short inside the coil. Then I'd check Ohms between your Neg post on the coil and ground. Should be very little connectivity/Ohms. If there is continuity then your coil is bad (internally grounded). You did say it turned over but didn't start? If it did start then that's a whole different thing......

Then check your condensor while it's still in place. There should be some resistance but measurable between wire and ground.

I might be way off base too. LOL

Well, for about a week before the wire fried and after the starter kicked, the car was basically running fine.

At low RPMs it had a tendency to want to stall when you gave it gas, unless you over-revved it. This developed about the same time the starting problem began. When the starter ceased working I was able to park on hills and/or push start the car, which worked for several days. I've had the battery unhooked since the wire fried, and haven't tried anything since.

The fuses on the control box did not blow, nor did anything in the front fusebox. Odd, eh?
The black wire on the negative terminal of the coil is the condenser wire; it's green but spliced with black wire before it reaches the coil.

Now, if the coil itself had internally shorted wouldn't I expect either the condenser wire or the red/black wire on the positive terminal to have burnt out as well?

Will try the tests on the coil tomorrow, and report back.
Also, am going to try and trace that tach wire frontward from the control box, in case it fried all the way up as well.
Anything else while I'm in there?

Thanks for all the help!

Cole

I checked the existing coil and read 3.6 ohms between positive and negative terminals. Are you sure that's indicative of a blown coil? The replacement coil I picked up reads at 3.5 ..

Thanks,

Cole

After reading through all this, it looks to me you had a short to ground on your tach wire. This would have nothing to do with the coil or condensor failing. The tach has a high input impedance and is probably not the problem. I'd suspect the insulation was damaged somewhere between the coil up to the dash and contacted ground. When the points are open, that small gauge wire takes all the current from the ignition switch through the small resistance of the coil if it's shorted to ground. It gets hot and the insulation melts, then can melt into other wires that it's bundled with. You did not see a fuse blow because I do not believe the wire to the coil +12V is fused, it's direct off the battery through the ignition switch.

I'd say you have two choices. One is to try to isolate that melted tach wire back to the fault working from both the coil end and from the tach end, then repair it. The other option is to disconnect it from each end then run a new wire from the tach back to the coil, and hope the short didn't take out any other wires in the harness when it got hot.

This is one of the problems with these 914s. There are many unfused circuits coming off the battery and if there's a short circuit to ground on any of them you are screwed. The fortunate cases are like yours and the wire just melts in half. The unlucky ones have a fire. Believe it or not, but the old American cars are much better designed on their electrical systems as they used fusible links on wires not directly fused (except for the 12V to the starter).