'64 Electrical Issue

[Dale M.]

Attempting to get my car out for the summer season. I had done quite a bit of work over the winter. When I screwed down by batter disconnect on my negative cable, the engine wiring harness started smoking. As I was already had a new one to replace it, but I wanted to get the headlights all working first ( Had rebuild the headlight motors and buckets).

It seemed to me that the engine harness going down toward the started had shorted out, as it was burned and stuck to the engine/bell housing. I replaced the harness. Now I wanted to ensure that nothing else is blown. In the '64 shop manual, the first check is to start the engine, set it on fast idle, then disconnect the negative battery cable. This is easy and I have a disconnect switch. When I disconnected the neg. cable, the engine stopped. Now I assume the alternator is not charging to keep the engine running. I took my alternator to Auto Zone and it checked out GOOD. Assumed that it must be the regulator. I put a new (not original, electronic) regulator on the car. I also must have destroyed my Pertronic's Ignitor, and put my points back in.

Now it seems if the car is shut off and the batter is connected, that after a few hours that the Alternator and regulator is getting warm. I assume some current is passing through these components. I suspect the Horn Relay is the component that should prevent electricity from flowing to the alternator and regulator? Is there a method to verify this? I did not find anything in my shop manual about the horn relay, but its the first point in the wiring diagram where the current from the battery, via the starter solenoid runs.

Thanks for any suggestions.

[Edward J.]

Re: '64 Electrical Issue

Dale, alot of times the coil positive wire will ground out against the top ignition shielding. and make a good wiring harness no good in a matter of about 3 seconds.

[Dale M.]

Re: '64 Electrical Issue

Ed, your are correct, it took about 3 seconds to fry my harness. I did not see any damage around the ignition shielding, but a very good point. Thanks for getting back to me.

[John H.]

Re: '64 Electrical Issue

I suspect the Horn Relay is the component that should prevent electricity from flowing to the alternator and regulator? Is there a method to verify this? I did not find anything in my shop manual about the horn relay, but its the first point in the wiring diagram where the current from the battery, via the starter solenoid runs.

Thanks for any suggestions.

Dale -

The horn relay (the two screw terminals on the buss) is the main electrical junction between the alternator and the battery, and is the power distribution point for the whole car; that screw terminal buss is "hot" all the time and performs no switching function of any kind. The relay portion under the cover with the two plug-in connectors on the bottom only operates the horns.

[Dale M.]

Re: '64 Electrical Issue

John, after checking the horn relay closely, I noticed that the 2 screw terminals are actually only one piece with two connectors. This suggest that electricity flows to the alternator and regulator all the time. From the wiring diagrams, it looks like these are two separate connections to the horn relay. Now thats cleared up.

So I must have some short pulling juice through these components. It may be in one of these components themselves or some other place downstream from here.

Thanks for you input, I am getting a little smarter as I continue my research and analysis. Dale

[William C.]

Re: '64 Electrical Issue

Make sure the ground in the wiring harness at the starter motor is connected to the starter bolt, not to the battery stud on the solenoid.

[Timothy B.]

Re: '64 Electrical Issue

Dale,

What other work did you do to the electrical system over the winter?

I would be looking at the alternator as one of the diodes may be shorted. I don't know if this shows up on a autozone test, the only way I know to test them is to take the alternator apart and test with a meter.

Check the battery cables like Bill suggested above, and put a test light between the negative post on the battery and the negative battery cable and unhook fuses and alternator/regulator until no draw. Be careful because things like the clock etc. draw currect all the time so it's a process of elimination.

[Jack H.]

Re: '64 Electrical Issue

Also, understand that a portion of your alternator is hot at all times (unswitched) and relies on the internal diode bridge to thwart current flow when the ignition is shut off. It is possible to have one (or more diodes) that have suffered EOS (electrical overstress) and be leaking sufficiently to foster a significant case of discharge.

These kinds of rare damage (wounded but not altogether failed) can be a challenge to diagnose as diode junction puncture can temporarily self-heal itself when you remove power from the device (disconnect it to walk it to an auto parts store to have it tested) and the junction damage not re-open until there's enough current/heat to re-trigger the puncture...

[Dale M.]

Re: '64 Electrical Issue

I appreciate the input and the items to verify. I will get on these tonight. I do have the ground cable attached to the bolt that holds the starter motor. Something with the alternator sounds like a possible cause. Since I do not have the correct alternator, its not to bad of a problem. The shop manual has some good directions on checking diodes. Thanks

[Jack H.]

Re: '64 Electrical Issue

Yes, bear in mind the shop manual's suggested tech checks for validating diode integrity is a real 'go/no-go' test intended to catch the grossly failed 'basket case' parts. The situation I'd described was a VERY unique condition that would most likely pass the quickie tech check given in the service manual (you have to remove power from the diodes in order to put a multi-meter on them in ohm mode)...

The only way you'd find what I was describing (partial junction puncture) would by putting each diode up on a curve tracer OR monitoring the waveform of the alternator's charging output on an oscilloscope while you exercised the alternator across it's dynamic range (RPM and temperature).

So, I'm talking about a rather rare situation. One we don't see very often...

[Dale M.]

Re: '64 Electrical Issue

Jack, yes I understand and really appreciate your help. They main issue I have detected is the alternator and I believe the regulator (not very much) were warm after the car had sat overnight with the battery connected. (I normally have my battery disconnect turn off). I will see what I can detect, but I don't have all the equipment of knowledge to perform all of the checks you suggested. We do have a member of our club that I will see tomorrow and he is very good on electrical. This is good experience and a learning situation for me. Thanks again for your help. Dale