PO'd 65 Alternator

[Bryan M.]

I didn't think alternators were so sensitive. I just recently purchased a correct "694" alternator for my car to replace the installed incorrect one. The incorrect one had been running fine. The last trip I made was a 100 miler and the car ran great. After the trip the car was parked and the battery switch turned to off. The car has been sitting quietly in its parking spot for 2 weeks until yesterday, I decided to crank her up and go for a spin. When I turned the battery cut-off switch to on, smoke started pouring out of the engine compartment. I turned off the battery switch and went to investigate. The 12R wire from the horn relay to the alternator fried! It appears to be the only wire in the bundle affected. It must have dead shorted somewhere, but I can't see where. The only determination I can find is that the alternator is the culprit. The alternator shows going to ground when hooking the meter leads to the 12R post and casing. But, I'm not sure if this caused the 12R wire to fry or is the result of the 12R wire short circuiting.

Has anybody had an alternator go "bad" like this from just sitting? If so, I'm sure glad I had the battery switch in the off position while the car was sitting. It could have been much worse. Burned car and house!

Any suggestions on how to proceed from here would be great. I do have an extra "good" replacement alternator to install.

The wiring harness is fairly new so, would digging out and replacing only the fried 12R wire be adequate?

Is there anything else I need to check?

[Donald O.]

Re: PO'd 65 Alternator

When the battery in my '67 kept going dead, and would not hold a charge even while driving, I checked every circuit. After installing a new battery, I put my dvm in series ( connected the leads for measuring amps) and proceeded to pull each fuse one by one to isolate the shorted circuit. When that didn't locate it, I disconnected the VR, it too checked good. Finally I checked the Alt. Yep, it had a short to ground. Took it to flaps and had it checked and bought a replacement, and one of the new electronic VRs as well. No the shorted original Alt and VR have been restored by John Pirkle and are still in a box in the garage 8 years later. My original alt was 37 amps and the FLAPS is 60 amps.

So......short story is the alt can will go bad.

I would get a new forward engine harness. Whatever wire the red wire was touching may also have been fried. Why risk it.

Don

[Bryan M.]

Re: PO'd 65 Alternator

When the battery in my '67 kept going dead, and would not hold a charge even while driving, I checked every circuit. After installing a new battery, I put my dvm in series ( connected the leads for measuring amps) and proceeded to pull each fuse one by one to isolate the shorted circuit. When that didn't locate it, I disconnected the VR, it too checked good. Finally I checked the Alt. Yep, it had a short to ground. Took it to flaps and had it checked and bought a replacement, and one of the new electronic VRs as well. No the shorted original Alt and VR have been restored by John Pirkle and are still in a box in the garage 8 years later. My original alt was 37 amps and the FLAPS is 60 amps.

So......short story is the alt can will go bad.

I would get a new forward engine harness. Whatever wire the red wire was touching may also have been fried. Why risk it.

Don

Don,
You're right about other wires being affected. I've been digging and separating the harness all morning. I've found that the 12R wire insulation melted and stuck to some surrounding wires insulation. The damage to the harness is between the horn relay and where the alternator wires break out from the harness. The wiring back to the firewall looks okay. I also noticed a spot on the inner fender well. I wonder what caused the alternator to fail so suddenly and severely?

[Jack H.]

Re: PO'd 65 Alternator

As you discovered, not all electric branch circuits are both switched and fused! Some are unswitched (like glove box and courtesy lamps). And some are unfused, like the alternator. A bad diode in the alternator's 3-phase rectifier can result in current drain even when the ignition switch is OFF.

Diodes are generally hearty critters, but they can suffer damage via EOS (electrical overstress, too much forward current) or excessive PRV (peak reverse voltage). Most of the time they fail open circuit, but that's not always the case... They can blow 'shut' providing a path whose resistance varies with the degree of damage.

That's one reason for having a battery cut-off switch on our classic cars who see long periods of disuse. It's also why designers began to incorporate fusible links at strategic locations in the wiring system after 1966.

Check out a Shark car and note the fusible link(s) that are built into the engine harness on the wires running from the alternator to the B+ side bar of the horn relay. In conjunction with the subject of this thread, you'll understand why that 'improvement' was made...

[Domenic T.]

Re: PO'd 65 Alternator

Bryan,
Keep the alternator case with the correct #s and transplant your parts from your old one to the new one.
I took my 37amp and installed the innerts of a higher amp alternator.

And YES I have seen this happen when someone tightened the nut attaching the wire to tight causing the plastic insulator to break grounding the wire.

DOM

[Donald O.]

Re: PO'd 65 Alternator

Bryan,
Keep the alternator case with the correct #s and transplant your parts from your old one to the new one.
I took my 37amp and installed the innerts of a higher amp alternator.

And YES I have seen this happen when someone tightened the nut attaching the wire to tight causing the plastic insulator to break grounding the wire.

DOM

The alternator case will still have the correct date and part number, but the visible diodes, with their date code's will also be visible, and one of the originals is shorted.

[Ronald L.]

Re: PO'd 65 Alternator

Consistent with alternator diodes, another failure mode on these original diodes is silent, you don't know until the car dies. In this case they just blow and you run on the battery for a while and then the car stalls suddenly.

[Bryan M.]

Re: PO'd 65 Alternator

The shorted out alternator on the car is of the FLAPS variety. I'm still waiting on the arrival of a correct 694 alternator. Sorry for the confusion.

After pulling everything apart and examining the surrounding wires for damage, I think I'm going to temporarily replace the fried 12R wire and install another good FLAPS alternator to make sure that takes care of the problem. I'm still going to order a replacement harness to install along with the 694 alternator when it arrives.

I'm also thinking about installing an inline fuse on this circuit while I'm at it.

[Richard M.]

Re: PO'd 65 Alternator

I use this type 40 amp circuit breaker on the solenoid lug to feed the main power lead. It comes in either 40A or 50A.

http://www.amazon.com/gp/product/B00...tomotive&psc=1

[Bryan M.]

Re: PO'd 65 Alternator

Thanks Rich. That looks like a good option.