1955 12V Alternator conversion GEN light on

[Critterpainer]

The bulb should be grounded by the dash. The issue is up the harness and why it's grounding at the alternator with the key off.

Ward. Thats NOT the way a "gen" light works. Turning on the Ign with the engine off puts power to the bulb from the battery. The ground is supplied by the generator NOT making a charge and allowing the bulb to ground by backfeeding through the Gen. When the car is running the Gen is making voltage that matches within a couple of volts of the battery voltage. Bulb has power to both contacts and no ground. Out goes the light.

 

[Ward 57]

Ward. Thats NOT the way a "gen" light works. Turning on the Ign with the engine off puts power to the bulb from the battery. The ground is supplied by the generator NOT making a charge and allowing the bulb to ground by backfeeding through the Gen. When the car is running the Gen is making voltage that matches within a couple of volts of the battery voltage. Bulb has power to both contacts and no ground. Out goes the light.

All I'm saying is that the light is grounded at the dash. You are correct on how the regulator works to extinguish it. It is getting power from someplace, I just have no idea from where as I have never done an alt. conversion.

 

[doug7740]

All I'm saying is that the light is grounded at the dash. You are correct on how the regulator works to extinguish it. It is getting power from someplace, I just have no idea from where as I have never done an alt. conversion.

Ward,

You are incorrect, it doesn't matter if you have a generator or an alternator, the generator light is not grounded at the dash. The generator light gets voltage from the black/green wire at the ignition switch. This is the same wire that supplies voltage to the oil light. The generator light gets its ground from the yellow/black wire that is connected to the voltage regulator armature terminal.

doug7740
1955 Thunderbird Blue

 

[Ward 57]

Ward,

You are incorrect, it doesn't matter if you have a generator or an alternator, the generator light is not grounded at the dash. The generator light gets voltage from the black/green wire at the ignition switch. This is the same wire that supplies voltage to the oil light. The generator light gets its ground from the yellow/black wire that is connected to the voltage regulator armature terminal.

doug7740
1955 Thunderbird Blue

I haven't been under the dash enough I've been thinking of the dash lights. If the gen. light is a two wire connection then agreed I'm off base. Still it's a head scratcher.

 

[jimntempe]

Ward,

You are incorrect, it doesn't matter if you have a generator or an alternator, the generator light is not grounded at the dash. The generator light gets voltage from the black/green wire at the ignition switch. This is the same wire that supplies voltage to the oil light. The generator light gets its ground from the yellow/black wire that is connected to the voltage regulator armature terminal.

doug7740
1955 Thunderbird Blue

That's correct. When the generator/alternator isn't spinning that regulator A terminal acts as a ground and current flows from the ignition switch thru the genBulb to the A terminal and to ground. When the Generator/Alternator starts spinning instead of it being effectively a ground that terminal gets voltage applied to it from the gen/alt. If the gen is going slowly and only generating say 8 volts it means that across the genBulb you have 12 volts from the battery on one side of the bulb and 8 volts from the gen/alt applied to the other side of the bulb. 12-8=4 volts. So the bulb is getting 4 volts and lights very dimly. That why at low idle speeds it will be dim instead of bright. As gen/alt speeds picks up to normal idle speed it puts out 12 to perhaps 13 volts and little to no current flows because the voltage differential across the bulb is near zero. As things stabilize the gen/alt also starts putting the same voltage to the battery (and therefor to the ignition switch terminal) as it does to the A terminal and the light has zero net voltage across it and no current flows thru it. When you convert to an alternator there are two ways to do it, one way, the one wire alternator, is "self-exciting" and you don't use the GenBulb... , the other kind gets it "excitation" thru that bulb, which is why it's not "one-wire". So if you use the external excitation style and don't hook up the light the alternator doesn't get "excited" and doesn't produce any current. I've seen this explained better but that's the best I can do.

 

[Critterpainer]

The basic issue still is that for some reason the GEN light is on with the IGN switch off. Does the light stay on with the engine running or does it go out? Either way does a volt gauge show that the ALT is working?

 

[Jeff55]

The basic issue still is that for some reason the GEN light is on with the IGN switch off. Does the light stay on with the engine running or does it go out? Either way does a volt gauge show that the ALT is working?

If I could start the car I could test the alternator to see if it is working. At this point there is not starting action when I turn the key.

 

[Critterpainer]

Has the car run under your ownership? If so is the battery charged? If the car has an automatic is the shift lever in Neutral as it should be (Not Park)?

 

[Jeff55]

The car ran before I started to swap out the generator for the alternator. The battery is charged. Not park because its an automatic.
I have is scheduled for a trip to the shop.

 

[Ward 57]

Has the car run under your ownership? If so is the battery charged? If the car has an automatic is the shift lever in Neutral as it should be (Not Park)?

Wow , all these questions and we don't even know if it runs. I would start there and work backwards but I'm just a shade tree mechanic but start from the source. The heart so to speak.

 

[Critterpainer]

Please let us know what the results are.

 

[Jeff55]

Well the soonest I can get it to the shop is the 17th. So, I went backwards and reinstalled the generator. The car runs fine. no light problem.
Switched back to the alternator and the light is on the same way (no key). But it started. I obviously connected something different. I have pictures from before I started and I followed the same directions.

Making progress.

Still going into the shop for compression test and valve adjustments. Maybe they can fix the GEN light while they're at it.

 

[Ward 57]

Well the soonest I can get it to the shop is the 17th. So, I went backwards and reinstalled the generator. The car runs fine. no light problem.
Switched back to the alternator and the light is on the same way (no key). But it started. I obviously connected something different. I have pictures from before I started and I followed the same directions.

Making progress.

Still going into the shop for compression test and valve adjustments. Maybe they can fix the GEN light while they're at it.

Everything If it were me, I'd drop the wrench and stick with the generator unless you have a greater load than the 30 amp generator can provide. Sometimes trying to upgrade to newer technology involves much more.
Ever try to just replace a sink drain? Once you touch something it goes down the line and it turns into a rats' nest. Hope you sort it out. I'm sure your shop supervisor is scratching his head also.
a compression test and valve adjustment can be done at home if you desire depending on your skills.