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Old 07-04-2021, 01:19 PM   #1
Thearne3
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Default Generator short?

Driving fine for 30 minutes, then big backfire, loss of power and won’t start. Heavy drain indicated on ammeter (10 amps). Driver side of terminal quite hot. I assume a short somewhere, so disconnected the terminal to cutout wire. That stopped the drain. Got home (towed by a friend) and did some checking:

1. No drain when wires normally connected to cutout are just connected to terminal box, but not cutout. No issue.
2. Checked cutout after removing from generator: no short there either.
3. Checked resistance from armature post to ground: zero resistance!

Do generators often develop a short in the windings or is it more likely the post has lost an insulator piece from the case? How is the post insulated from the case on the inside? I see an insulator ring below an insulating washer on the outside, but is there a similar insulating ring or washer on the inside of the case?

Finally, would a short in the generator cause other things to fail? Headlights (which were on) seem to be dead except for one parking light. Running tail lights all work. All lights are LED. Car still doesn’t start. Could the condenser or coil be blown?

Thanks for your advice!
Tom
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Old 07-04-2021, 02:05 PM   #2
nkaminar
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Default Re: Generator short?

Without connecting the generator (cutout) check to see if you are getting voltage at the two posts on the terminal block on the firewall. There is a rubber grommet that is use to insulate the armored cable as it enters the terminal block. If you don't have that it could be that the posts inside the terminal block shorted to the armored cable. If that is all good, check to see if you are getting voltage at the moving point with the points open.

Regarding the generator. There are insulators all around the output post. There will be a low resistance to ground at the post when things are OK which may look like it is grounded depending on the scale used on your ohm meter. To double check, put some paper under all three brushes inside the generator and check again.

LED's will burn out if they get a big spike. Take the bulbs out and test with a battery that is hooked up correctly to the bulbs. If you have the wire disconnected to the cutout then there is no electricity getting to the light switch. Take the two wires that normally connect to the cutout and tape them together with electrical tape and try the headlights. Tape the wires so that no metal is exposed that can short against something.

There could be a short where the sockets enter the headlight buckets that will look like a fault with the generator or cutout.

The coil or condensor could have been blown if there was a big spike but check for voltage at the points first before you start replacing things.
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Old 07-04-2021, 02:09 PM   #3
Patrick L.
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Default Re: Generator short?

Download a copy of the wiring diagram and you can trace down the issue with a test light or volt meter.

If you think the issue is the generator then disconnect it and feed power to the output terminal. If there is a spark/short then thats not a good thing and the generator needs to come apart. With the fan belt loose and power applied the generator should spin slowly, if it does then the generator should be fine and the problem is elsewhere, like in the headlights, etc.
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Old 07-04-2021, 04:08 PM   #4
Thearne3
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Default Re: Generator short?

Thanks for the replies!

Connected power to Armature without cutout and loose fanbelt: generator turned quote nicely, so not the generator (note to self: low resistance is fine!)

Turned on ignition and checked points: small spark when moving the plate back and forth, so power is coming from ignition. I do have the rubber grommet in the terminal box, so unlikely a short from the armored cable.

There must have been some sort of power surge. Both LED headlights are blown, but not the LED taillights. I suspect the condenser may be blown. I have the Nu- Rex modern points/condenser plate. Is there any way to test the condenser? Or Coil?

Thanks again.
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Old 07-04-2021, 05:46 PM   #5
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Default Re: Generator short?

Update:

Rechecked the ignition voltage: 6.3v at terminal (both), coil (both sides), points with and without condenser. All good.

Checked the fuel, just to be sure and it flowed well.

Started the car. Sh#t. Now I really don’t know what went wrong!

Two possibilities:

Intermittent short in the headlight harness (checked the connections at the headlights, looked clean. Replaced the bulbs, headlights working again.)

I assume any short drawing 10 amps (as measured by the ammeter) would affect the ignition?

Is a bad coil a possibility? I’ve heard they can short out when warm. But would that affect the headlights?

Still a mystery!
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Old 07-04-2021, 05:53 PM   #6
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Default Re: Generator short?

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You could have a”rubbed” wire somewhere in your open wiring harness that’s just clipped to the frame. I actually prevented a short by noticing a frayed wire rubbing on the frame in the left side of the engine compartment.
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Old 07-04-2021, 07:47 PM   #7
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Default Re: Generator short?

Those damn intermittent shorts can be a bugger to find. Try wigging things. It sounds like you do not have the fuse that mounts next to the starter switch. They are cheap insurance and easy to install. See https://www.snydersantiqueauto.com/P...earchByKeyword.

For future reference, the way to test the condensor is to use an ohm meter. It should not be shorted. When you first connect the meter it will indicate low resistance as the condensor starts to charge and then high resistance when it is charged. You will get the same readings when reversing the leads on the meter. You can go back and forth with the leads on the meter to confirm it is OK. An analog meter works best but a digital meter can be used. If you only get an open reading on the condensor or it is shorted then it is bad. The condensor should be removed for testing. To see the condensor charging with the ohm meter, try different scales.

The initial big backfire is some sort of clue. I have no idea what it means, but it means something.
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Step on the gas, for tomorrow I die.
Forget the brakes, they really don't work.
The clutch always sticks, and starts with a jerk.
My car grows red hair, and flies through the air.
Driving's a blast, a blast from the past.

Last edited by nkaminar; 07-04-2021 at 08:15 PM.
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Old 07-05-2021, 05:29 AM   #8
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Default Re: Generator short?

The initial big backfire is some sort of clue. I have no idea what it means, but it means something
end quote


LOL. Yep.
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Old 07-05-2021, 05:31 AM   #9
Patrick L.
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Default Re: Generator short?

Since you mentioned the headlights were on, I think I'd start there especially if the original type connectors are used. Those things are troublesome. I get rid of them, I don't care for them.
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Old 07-05-2021, 05:50 AM   #10
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Default Re: Generator short?

In 1970 on my way home with my new to me A, an hour and 1/2 into my trip an hour 1/2 to home, I bounced over a RR crossing and the car quit running. Pulled over and turned key switch off, now what to do? after a while turned key back on and it started.
That key switch would intermently turn off and back on, some times with a loud back/after fire, good time scaring people around the car lol. After the car was in storage a few years it wouldn't start, I jumped around the switch and it started.
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Old 07-05-2021, 01:01 PM   #11
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Default Re: Generator short?

A problem in the ignition power feed could cause an after fire. It sounds like a quick short caused the whole system to shut down momentarily.
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Old 07-05-2021, 01:53 PM   #12
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Default Re: Generator short?

Thanks for all your replies!

Nkaminar: I had a fuse, but hadn’t installed it (sigh), so I’ve taken your advice and done so!

Patrick L: you mention the headlight connectors. I’ve disconnected and looked at each. Not sure what I’m looking for, but see no evidence of carbon or melting, etc, if short were there. If you replaced them, what did you use?

Big Hammer: I recently replaced the ignition switch with an original pop out restored by one of the long time members here, so I’m hoping that is not a likely candidate.

Finally, the headlights, though now working, are flickering. The parking lights (not cowl) are fine, so I believe the ground is good. This, again, points to the headlight harness, so that’s where I’m going to focus.

Thanks again, will report back…
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Old 07-05-2021, 03:02 PM   #13
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Default Re: Generator short?

Quote:
Originally Posted by Thearne3 View Post
Finally, the headlights, though now working, are flickering. Thanks again, will report back…
Is that w/the engine running? Or not?

DON'T run the engine w/the generator disconnected!
If you want to do that, disconnect the wires from the output terminal of the cutout and insulate them, then put a jumper between the generator output terminal and ground.
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Old 07-06-2021, 09:00 AM   #14
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Default Re: Generator short?

Quote:
Originally Posted by Thearne3 View Post
Finally, the headlights, though now working, are flickering. The parking lights (not cowl) are fine, so I believe the ground is good. This, again, points to the headlight harness, so that’s where I’m going to focus.
Parking lights draw a lot less current and may not be affected as much by a bad ground. Temporarily wrap some wire around the conduits and connect the other end to the frame somewhere. If lighting improves, you've found the problem.
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Old 07-06-2021, 09:36 AM   #15
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Default Re: Generator short?

I would start by disconnecting the wiring connector from the bottom of the steering column. If still a short then continue to measure remaining components with a multimeter. Intermittent shorts are difficult to locate.
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Old 07-06-2021, 09:37 AM   #16
nkaminar
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Default Re: Generator short?

The fix for the headlight sockets is to gut the insides and run the wires to inside the headlight bucket. Then use separate wire connectors and bullet ends, see link below. You have to take the lens and reflector off to disconnect the wires.

The ground has to be good. I use a copper bearing electrical grease at any connection points. Make sure everything is shinny and tight. In my car the ground is under the spring for the screw that focuses the headlights, but this is not an ideal solution.


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A is for apple, green as the sky.
Step on the gas, for tomorrow I die.
Forget the brakes, they really don't work.
The clutch always sticks, and starts with a jerk.
My car grows red hair, and flies through the air.
Driving's a blast, a blast from the past.
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Old 07-06-2021, 02:22 PM   #17
Patrick L.
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Default Re: Generator short?

I use quick connectors [ trailer ]. and run grounds from the sockets to a good frame ground.
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