Is this a bad coil?

[skkroosw]

Two issues could be going on here that are preventing this '69 c10 from starting while cranking. Pretty sure #2 is a problem, but also #1 could be going on.

1. I am not sure the test indicates a functional coil. I think there should be a resistance from the + terminal to the top wire leading to the distributor, but it tests open.

2. A wire may be missing at the coil. There are atleast two loose wires nearby, but I thought they've always been there loose. However, I think a resistance wire OR a wire+resistor from the ignition is needed to power the coil when the starter is not turning... BUT, the truck doesn't start so I suspect #1 is also a problem. I test no voltage on the coil (+) in the run position.

thanks!

[BigBird05]

You need 12v from the starter R terminal and 9 v from a ignition 1 source. So if you have only one wire on the + terminal on the coil you are missing a wire. Fix that first then move on to the next problem.

[CastIron]

If I remember correctly, there is only one wire attached to the positive side of the coil. The resistor wires goes from the bulkhead connector down to the starter, then a regular wire goes from the starter to the coil. You should have some voltage at the coil, but it may not be 12 volts, depending on whether the points are open or closed. I would start by checking the fuses first, and making sure they have voltage on both sides. Then check the large connector near the master cylinder. The resistor wire is usually a braided looking wire, so if you can find that measure from the large connector to the positive coil terminal. It should have some resistance, but not a lot. If it has no continuity, that is the problem.

[dmjlambert]

The resistor wire is a cloth covered wire that normally goes from the bulkhead connector into the tape-wrapped engine harness. Shown as 20W/OR/PPL on wiring diagram, but probably faded to white. Inside the engine harness it is attached to 2 yellow wires. One of the yellow wires goes to starter, and one goes to the coil. The engine harness is covered with tape up to the clamp at the rear of the engine at one of the transmission housing bolts. From there the yellow wires go to coil and starter. This is how it was on my 1969 truck. Since you have a blue wire perhaps you have some patched or replaced wires. Here is the wiring diagram and pictures.

[mr48chev]

Well I learned something today.

As many of these trucks that I have worked on and as many as I have owned (3 running and driving) I never noticed that. If by chance the Orange with purple tracer wire runs directly to the coil you don't have the resistor bypass working.

I've run into other point igniton Chevrolets that do not have power to the coil from the switch when they are in start position relying on the resistor bypass on the solenoid to provide 12 V when cranking.

Here is a link to testing a coil https://atlib.info/blog/176-how-do-i...-ignition-coil

My regular go to ignition test procedure papers are out in the garage and it's too late to dig them out tonight.

[racerop]

Originally Posted by skkroosw

1. I am not sure the test indicates a functional coil. I think there should be a resistance from the + terminal to the top wire leading to the distributor, but it tests open.

thanks!

This is the very definition for resistance



A coil should read a low resistance , so your multi meter needs to be on a small scale. But should read less than 300 ohm but more than 1 ohm


What do you mean when you say “open”

[skkroosw]

Originally Posted by racerop

This is the very definition for resistance



A coil should read a low resistance , so your multi meter needs to be on a small scale. But should read less than 300 ohm but more than 1 ohm


What do you mean when you say “open”

By open, I mean the multimeter reads null on the 20 ohms and lower setting -- which means it is more than 20 ohms or even infinite \ open circuit. I wasn't quite sure how coil works, but I thought I saw testing online of 2-3 ohms from (+) terminal to distributor wire... and I don't get that.

THANK YOU for the replies so far. I'll investigate closer today and update.

[LockDoc]

Originally Posted by CastIron

If I remember correctly, there is only one wire attached to the positive side of the coil. The resistor wires goes from the bulkhead connector down to the starter, then a regular wire goes from the starter to the coil. You should have some voltage at the coil, but it may not be 12 volts, depending on whether the points are open or closed. I would start by checking the fuses first, and making sure they have voltage on both sides. Then check the large connector near the master cylinder. The resistor wire is usually a braided looking wire, so if you can find that measure from the large connector to the positive coil terminal. It should have some resistance, but not a lot. If it has no continuity, that is the problem.

You would be wrong on that. There has to be 2 wires to the coil. The resistor wire does not connect to the starter solenoid. The Yellow wires connect to the starter (R) terminal and supply a full 12 volts to the ignition coil while the solenoid is engaged. (cranking) When the key is released and returns to the RUN position the coil then gets power through the resistance wire coming directly from the ignition switch through the bulkhead connector to the coil.

LockDoc

[kwmech]

To answer your question, yes, you should have continuity

[custom10nut]

SUV’s for future reference