Battery Discharge

I’ve double and triple checked the wiring but it appears I have a 5 amp or so discharge when my T is running. I does not have any electric lights so that cannot be the problem. Also not sure how accurate the ammeter is. I will be testing more this weekend. Any suggestions? Thanks in advance. Bob

Is it possible that the ammeter is connected backwards?
I assume that you have a 6 Volt battery and generator setup.
Compare the battery voltage before you start the engine and while the engine is running.
If the battery voltage is higher while the engine is running - the battery is charging.
If not, then battery is likely discharging.


I did check the wiring to the ammeter and it looks correct. I will double check over the weekend and report back. Thanks for the reply.

Model T electricity is my sole area of expertise.
Correct Ammeter charge and discharge wiring wiring is a very common problem.
Give me a call tomorrow after 11 am EST and I will show you how to conduct two very simple tests to see if all the charge and discharge circuits are wired correctly.
Attached is a correct wiring diagram I commonly use because many others are confusing or wrong.
Ron Patterson

Thanks Ron, I will be out of state Saturday returning on Sunday. I will check my wiring against your diagram and thought I would check for charging at the battery with a volt meter. I will post back here. And see about getting in touch with you at that time. So happy to find you here and again thank you for offering help. I’m sure I will be contacting you.

I checked the wiring against the diagram posted and it looks good. I put a analog volt meter on the battery with the car off and it registered 6 volts. Started the car and the meter still registered 6 volts but the ammeter registered a discharge. I am also experiencing difficulty in switching from bat to mag. Do I have a bad ammeter or switch? The car has new wiring harnesses. I rewired both of my Ts at the same time. My 26 pickup runs like a Swiss Watch.

This is a stab in the dark and I am sure Ron can provide a better insight.

I am thinking that the battery is “motorizing” the generator.
The cutout should prevent this.
Try swapping the cutout from your other T.