Voltage Drop...Ammeter?
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3rd Gear
Joined: Oct 2025
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Voltage Drop...Ammeter?
I have been trying to trace the source of a voltage drop/loss in my charging system on the '59. All components show charge (13.5 volts running and increasing with increasing rpm), Voltage Regulator, Generator. Problem is I'm only getting 12.5 volts at the battery which is the same as the engine not running and no increase in voltage with increase in rpm. I have traced it to the Ammeter, I think. On the red wire side (passenger) I'm getting 13.5 volts with the engine running. On the black wire side (driver's) I'm getting 12.5 volts just like the battery shows. Is it possible to have a voltage drop across the ammeter and should both terminals show the same voltage? Is it a sign of a bad ammeter??? Thanks for any advice.
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You should have the same Voltage on both Ammeter terminals. Are the nuts on both terminals tight?
Does the Ammeter ever deflect to the right at all when the engine is running at a high idle? Or to the left if, say, the headlights are on and the engine is off? If "no" and "no" (in that order), then a likely cause is a failed Ammeter.
Does the Ammeter ever deflect to the right at all when the engine is running at a high idle? Or to the left if, say, the headlights are on and the engine is off? If "no" and "no" (in that order), then a likely cause is a failed Ammeter.
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Thank you for your reply, Jim. The ammeter does deflect to the negative (discharge side) slightly when the headlights are turned on. The deflection to the positive side is hardly noticeable or insignificant. I'm confused....although I'm feeling pretty certain that my problem is here. I can see why the black wire shows battery voltage because it's connected to the battery via the starter. I just don't know how the battery is maintaining it's charge...particularly on our recent trip to Sacramento. Perhaps there's resistance in the circuit allowing just over 12 volts to pass???? Or I'm just lucky. I think the connections are tight, though I don't know how clean. I'm going to disconnect the ammeter and check the resistance. Any idea what value that should be?? At the same time, I'll connect all the wires together and see if that restores my charging ability. At that point I guess I'll just open the ammeter and see if I can see corrosion or a poor connection and/or replace it.
Eric.
Eric.
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Where are you connecting to ground when you make this measurement ?
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Joined: Feb 2007
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From: northern california
C2 of Year Finalist (track prepared) 2019
Thank you for your reply, Jim. The ammeter does deflect to the negative (discharge side) slightly when the headlights are turned on. The deflection to the positive side is hardly noticeable or insignificant. I'm confused....although I'm feeling pretty certain that my problem is here. I can see why the black wire shows battery voltage because it's connected to the battery via the starter. I just don't know how the battery is maintaining it's charge...particularly on our recent trip to Sacramento. Perhaps there's resistance in the circuit allowing just over 12 volts to pass???? Or I'm just lucky. I think the connections are tight, though I don't know how clean. I'm going to disconnect the ammeter and check the resistance. Any idea what value that should be?? At the same time, I'll connect all the wires together and see if that restores my charging ability. At that point I guess I'll just open the ammeter and see if I can see corrosion or a poor connection and/or replace it.
Eric.
Eric.
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I think the jumper will show you if the ammeter is bad. I believe it is or something between the black wire at the ammeter and the starter connection See if your lights come on without the engine running. It sounds to me your generator is running the lights etc. but not charging the battery..The generator connects to the battery through the ammeter. The battery runs lights etc. through the ammeter. Without the engine running, the ammeter should show significant discharge with headlights on. If you just use the battery to start the car, it's probably good for many starts without being charged.
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