New wiring harness question at coil

[Lugnutt]

I've been having some intermittent ignition fails while driving my stock 72 Chevy 350. I recently had a couple of new wiring harnesses installed under the hood and am still having the problem. While looking at the wiring around my coil I notice a couple of things I don't understand. Please if you guys can, explain this to me.

On the negative side of my coil I have an original brown wire going to the firewall behind the engine. I also have the black wire to the distributor.

On the positive side of my coil I have a yellow wire spliced into the same fitting as the fabric resister wire. As part of this taped section of my new wiring harness I also have a blue wire with a hooded plug end attached to nothing (extra??).

Also attached behind my existing coil bracket is what looks like a capacitor with a wire just long enough to attach to one of the coil leads. What is the function of this capacitor, which side of the coil does it attach to, and could it be my intermittent ignition problem if it was starting to fail.

Lastly, does anybody know what that extra blue wire in my new wiring harness is supposed to be for.

Some advice on this would be greatly appreciated, thanks

[ray_mcavoy]

The unused blue wire with the rubber boot type connector is most likely for an oil pressure light switch. If you truck has a factory oil pressure gauge it won't have an oil light that would make use of that wire.

The capacitor attached to the coil bracket is only used to help prevent radio interference from the ignition system. It would have originally attached to the positive side of the coil.

Is the black wire that connects the negative side of the coil to the distributor still an original wire or has that been replaced too? The reason I ask is because the end of that wire (inside the distributor) flexes a little each time the vacuum advance moves. And over time that can cause the strands of the wire to break and result in an intermittent connection.

[Lugnutt]

Thanks for your response Ray,

The black wire to the distributor is new and has a rubber sheath around it, so I'm assuming it's ok.

This radio capacitor at the coil; is it the same type of capacitor as the one installed with the points in the distributor? Might as well change that as well.

[ray_mcavoy]

Originally Posted by Lugnutt

This radio capacitor at the coil; is it the same type of capacitor as the one installed with the points in the distributor? Might as well change that as well.

Yes, it is the same type of capacitor although I'm not sure if the capacitance values (in microfarads) are the same or not. I think the length of the wire lead is a little shorter on the capacitor that goes inside the distributor as well.

If that radio interference capacitor has an internal short circuit it could cause problems. But simply leaving it unhooked should not be causing any issues. In fact, vehicles that came from the factory without a radio did not even have that capacitor installed.