356B T5 Roadster Battery is losing its charge

[David Descoteau]

In need of help with a battery issue on my 356B T5 Roadster. Just completed a full transmission rebuild. The car had been converted to a 12V system when it was restored 25 years ago.There were a few electrical issues that were sorted out with the rebuild, directionals were not fully operational and now work fine and the 6V wiper motor after putting in a 12V amature now functions NOW, the problem is the battery which for some reason is drawing amps and losing it charge with the ignition switch off and no other electrical systems on.

The ignition switch was just replaced do I don't know if this could be the problem. Anyway, the mechanic who did the transmission is not really an expert on electrical issues so I don't know if something went wrong when he corrected the directional and wiper motor problems.

[John Brooks]

Put a multimeter set on AMPS, pull off the positive battery cable, put the red lead on positive battery post(+) , and the black positive cable (-). See what the draw is in amps. then remove the fuses one at a time until the amps drop to zero. That's the bad circuit.

Then look at the loads, bulbs on that fuse, disconnect them one at a Time until it draw goes away.

You may have more than load, so as you pull the fuse watch the meter drop. If it goes from 1.2 down to 0.8 you have a .4 on the removed fuse, but another .8 on another.

If you don't have a meter, a bulb with two wires work also. The draw will light the bulb in series with your draw, until the fuse is removed

It's just electricity,

[Doug McDonnell]

Make sure transmission to body ground strap is connected.

[David Jones]

John has laid out the best way to find the current drain but just thinking out loud I would check the wiper motor because it was worked on it is something to consider. The wiper motor stops as a result of the circuit being opened by a contact on a cam in the wiper motor when the wiper switch is turned off. If this switch contact does not break fully but there is enough resistance to movement to slow it down enough that it stops but not completely break circuit it is I guess possible for a small draw to take place across the points while not being enough to drive the motor but enough to kill the battery. Just a wild ass theory.

[Geoff Fleming]

With everything turned off, disconnect the ground from the battery and connect a test lamp between the negative pole and ground. It should not light. If it does light and all electrical items are turned off, there is a short somewhere. Sometimes removing the fuses one by one and observing if the test lamp goes out can help in spotting the short.
A dying regulator will also not allow the battery to re-charge and can be the source of the problem.
Remove the positive battery cable and if you don't see clean copper at the clamp, cut the cable back an inch and then replace the clamp with a new or very clean one. The ground strap should be attached to clean, shiny metal and the clamp end also very clean. The car needs a clean wiring system, well grounded, in order to work as it should.
The battery should show about 14v with the engine held at 2,500 rpm, ( if a 12v system...about 7volts for a 6v system). If less, the generator or regulator are the suspects.

[David Descoteau]

Thanks to all who replied. Problem is fixed. The wiper motor was the problem The motor is the original 6V system. When the car was converted to 12V's the wiper fuse keep blowing out. We replaced the armature with a 12V and the wipers worked but caused the draw on the battery. Solution, remove the wiper motor fuse.

[Wes Bender]

David Jones nailed it. Whenever I have an electrical glitch, the first thing I check is the most recent thing I worked on....... or one of the most recent things.