What would cause this wire to burn up?

[4thgencreamsicle]

‘69 c10 sb w/points and no plans for hei as of right now.

I’m talking about the cloth covered resistive wire from the firewall that splits into the 2 yellow wires that head to the starter and coil respectively. No idea what that specific wire’s name is.

Went to crank it this afternoon and saw a small puff of smoke. It fried the 2 yellow wires from the crimp connection at the cloth covered wire all the way down. I saw in other threads how to go about replacing it, but right now I’m wondering why it happened in the first place. Ideas?

[kwmech]

Old and tired. I had the same thing happen in my 69. Never found what caused it. I had plans of converting to HEI and the plans were stepped up that day. New spark plugs, wires and the HEI itself. I was running again in about 2 hours

[VetteVet]

Those wires are not fused so to burn like that they would have to be grounded some place.
When you turn the ignition key on you allow positive current from the battery directly to the starter and ignition coil.
The purple solenoid wire doesn't seem to be burned so I would rule out it being grounded.

Here is what I would do.

1. Disconnect the negative cable at the battery.
2.Connect a voltmeter, set to test continuity, between the burned wires and ground.
3. See if your reading is zero ohms. This would indicate a direct short to ground.
4. If zero or very low ohms, disconnect the + coil wire and read higher than 1.8 ohms.
5. If still zero disconnect the wire at the starter, outside terminal R, and repeat the
reading.
These two checks will eliminate the starter, and the coil/distributer circuits
6. If you still have zero ohms, then disconnect the firewall block and read the meter.
7. If still zero then your short is not in the cab, the starter, or the coil circuit, but the
wires in the engine bay which may be against a manifold or exhaust pipe.

Take these readings and get back with the results.

[4thgencreamsicle]

Go easy on me as I suck at electrical but I am trying learn and Google every stinking step.

The pic shows the multimeter setting I am using (200ohms) and when I touch the leads together it goes from a 1 at the left of the readout (shown in the pic) down to about 0.2 (continuity right?).

So then I disconnected the neg cable from the battery (pos cable still on) and now touching the red lead to the burned section of wire and the black to the negative post on the battery I still get a reading of 1.

Not a zero/near zero like I was looking for. Did I do it wrong or does that help on where to go next.

[bhap]

One of the settings on you multi-meter should produce a buzz when you touch positive and negative probes. It might by at 2000 (that looks like the symbol on mine that does it) or it might be all the way over at the step shaped line. If you can find that - or see a zero when you touch pos and neg probes together, that is how you want to test the wires. One probe on the wires, one to a ground on frame or engine or bare metal. I would pull the harness out, strip the tape off and replace any bad wires. I've never replaced a resistance wire, but think they would be available or you could use regular wire and a resistance block of the correct resistance. One possibility is that the connectors on the ignition wire were corroding or dirty and created "extra" resistance in the wire (resistance creates heat) and caused it to melt. If the wire got that hot in one spot, chances are there is other damage.

[VetteVet]

You are doing pretty good, but you need to have the multimeter on the lowest setting and the black lead should be touched to a good ground like the frame or the engine block, like Bhap advised. The black lead touching the battery terminal isn't going to work.

If you had a grounded wire off the key switch you wouldn't want to install an HEI distributer cause it would burn up the module in the distributer.

Here's an excellent thread on the ignition wiring. It should be some help.

http://www.67-72chevytrucks.com/vboa...d.php?t=708975

[4thgencreamsicle]

Originally Posted by bhap

One of the settings on you multi-meter should produce a buzz when you touch positive and negative probes. It might by at 2000 (that looks like the symbol on mine that does it) or it might be all the way over at the step shaped line. If you can find that - or see a zero when you touch pos and neg probes together, that is how you want to test the wires.

I’m out working on the truck today and turns out none of the settings create any noise on our multimeter (maybe because it’s old?) I even tried finding the owners manual online to maybe see what Craftsman says is the setting for testing continuity on this model. I couldn’t find it so tried both the 2000 (with the symbol beneath it) and the stepped down line like you suggested.
The 2000 setting reads 001 when the probes touch and the line shape reads 001 no matter if probes are touching or not. The 200 setting gives me either 00.2 or 00.3 depending on how still I hold.

Maybe time for a new multimeter? Maybe one that will beep for me so it makes this a no brained? Lol

Vettevet, I went ahead and took readings even though I’m not sure now if my multimeter is even being helpful. Found a good place on the frame (thanks for that), and took some readings. They all read like when the test probes are touched together. For now I just tested the burned wires as they come off the resistance wire.