Dave Cunningham

My 67 roadster has just developed a new problem. The last few times I have gone to start it, the battery is stone dead, so I replaced the battery just to eliminate that right off the bat. Still going dead overnight, the alternator is charging at 13.6 at idle, a friend told me to hook up a test light between the negative terminal and the ground cable and if it lights ( car shut off) that there is a draw somewhere, and sure enough it does light ( brightly) he then told me to check the alternator case for magnetism to see if it could be a bad diode, and it is not magnetic at all. All the engine wiring is brand new and all the connections are good, just wondered if there is a quick way to diagnose this problem.

66jack

If you have the shielding on/over the dist/coil...

Take it off and check the wires that connect to coil...sometimes the shielding, 'nicks' the wire/s...worth checking...

PAmotorman

it should put out 14.5 volts revved up. just pull one fuse at a time with your test light connected and see if it goes off.

Powershift

Start by pulling fuses one at a time. Also check for any lights at night and also check to see if the glove box light is warm/hot indicating it is always on.

Pull the heavy red wire off the alternator and see if this stops the current flow. Is so, diodes are bad.

Last resort is to check the wiring diagram and see where you have any other unfused power sources, and then check them and disconnect them one at a time.

This is the only way I know, and the way most of us have been doing it for decades.

Larry

65GGvert

A sure way to find out if it's your alternator diodes is to disconnect the red wire to the alternator. If the draw goes away, you'll know for sure. If the draw is still there with the alternator disconnected, you can go further.
The only thing that should draw current with the key off (providing you have a stock radio and no aftermarket devices hooked up or plugged in) is the clock. Things that have power available with the key off are:
glove box light
brake lights
courtesy lights
tail lights and dash lights, if the switch is pulled on
cigarette lighter
headlight rollover switch

The two most likely are glove box light not going off, and alternator diode leaking. Both are easily checked. Pull open your glove box and immediately feel the bulb. If it's hot, it was on before you opened it.

65GGvert

Also remember that on a roadster, there's a cargo light on the rear wall behind the top. It comes on when a door is opened and is wired in the same series with the courtesy lights. If your courtesy lights work correctly, that one should be ok.

Dave Cunningham

Thanks guys, I took all your advise and here is where I am at:

I hooked up my meter in line with the negative battery terminal, and switched it to the amperage mode. The system was drawing 3.5 amps, so one at a time I pulled the fuses, checking each time, and nothing changed.
So I pulled off the red wire on the alternator and still no change. Then I pulled the grey plug off the back of the alternator, and it dropped down to less than half an amp, which I am assuming is the clock. So does this mean there is something wrong with the alternator? It is a freshly restored unit, Seems unlikely.

65GGvert

I think the plug you discussed goes to the voltage regulator, but someone with experience with that portion of the system needs to help you. In my experience, when you pull the red wire and the alternator diodes were leaking, it stopped. The voltage regulator connects from the 12v battery wire to the alt, so I suspect something there, but again someone help here.

65GGvert

kcust62

3.5 amps is a significant constant current draw for a light bulb to be on...57 bayonets (glovebox light-max draw about .25 amps) 1157's (tail light bulbs-max draw about 2.1 amps w/both filaments lit). It certainly sounds like a shorted wire to me, if not the alternator diodes.

PAmotorman

there is a switch in there that is not shutting off. send it out to be fixed

Powershift

Dave:

Problem could be in the alternator, the regulator, or the ignition switch. When the ignition switch is "off" no 12 volt power is sent to the regulator....which in turn goes to the alternator field. But when the ignition switch is turned "on" power is supplied to the regulator and then to the alternator.

So I would first check my alternator gray connector contacts to see if 12 volts (or so) is present to the field contact connector when the ignition key is turned off and on. That will let you know about the ignition switch. This should be the terminal with the dark blue wire. Use care and insulated clips or probe to avoid contacting other terminals or connectors. Ignition switch on is voltage at the blue wire connector and ignition switch off is no voltage at this connector.

If this test checks out okay, then the best I can recommend is to refer to the 1967 Chevrolet Service Manual Section 6Y for various test procedures that are given to checkout the regulator and alternator.

I sounds to be like an ignition switch or regulator at this point, but I am not sure without further testing. Again, this assumes that the alternator diodes are not causing the problem, which your earlier test removing the 10 gage red wire from the alternator terminal showed no amp change on your volt meter (or no diode back flow).



Larry

redstar

Disconnect the Pos Batt cable at the Batt terminal. Connect an ohmmeter between the Pos cable and chassis ground. Start disconnecting fuses and other positive wires until the resistance increases to over 1000 ohms!

buns

65GGvert......the wiring diagram you posted in post #9 is not correct for a 1967 Corvette. Wire colors are wrong. Should be as such:





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Dave Cunningham

Thanks, Larry and everyone else, I solved the problem without spending a dime. Over the weekend I was thinking about the issue, and it seemed to be pointing at one of three things , the alternator, voltage regulator or the ignition switch . And I have my old alternator and voltage reg, that were only changed out for NCRS correct units. So I figured the voltage reg was the easiest to swap in, and sure enough it eliminated the draw. I pulled the cover off of the new reg and after a quick inspection, noticed that one of the electro-magnetic contact points was always in the closed position, gave it a little tweak , swapped it back in , and everything is good.

corvetteed

It is always good to get an update so we know what happened. Thanks for posting.

SWCDuke

The clock only draws power when the rewind solenoid is energized unless it's a quartz conversion.

There is a normal leak path through the alternator, but it should only be about 10-20 ma.

It could be a set of welded points in the regulator. Try disconnecting it and see it the leak goes away. If it does remove the regulator and cover to see if any of the points are closed. None of the regulator coils should be energized with the key off and the regulator connected.

It may not be a bad idea to buy a generic replacement regulator. They are relatively cheap and it's always good to have a spare around. If a replacement regulator doesn't solve the problem, then it's likely a bad component in the alternator.

It's fairly easy to remove and disassemble the alternator and run all the electrical checks that are in the COM, which should reveal the bad component.

Duke

P. S. Never mind Dave - didn't see your last post, but at least my nose was on the trail. If that set of points stuck once, it could happen again. Dressing them down with a fine file might give them additional life.

cardo0

Good find and congrats! Just a suggestion that relay technicians use what is called a contact burnishing tool to clean contacts rather than replace them. Since you already got inside the regulator you may consider cleaning the contacts. Just Google contact burnishing tool as there is a large range in pricing. BTW 500 grit or greater paper would work.

BTW isn't your car a generator car rather than alternator? I thought all cars with a regulator had generators and alternator cars are regulator combined inside?

Frankie the Fink

No, C2s have alternators with external regulators (if stock)...
Generators (also with external regulators) went away after '62...

buns

Apparently that is not a good idea. From the Service Manual:





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