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TR2/3/3A Arcing & Sparking at the battery terminal to ground

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Jim_Stevens

Jim_Stevens

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Carrying this over from my last posting on my starter/Ring Gear problems, when I went to connect the +12v battery terminal back to ground (always the last step, and this is a positive ground car) I got arcing and sparking.

My bad, because I had inadvertently left the negative battery lead that goes to the starter solenoid off and touching the body. After reconnecting that lead, though, and now extremely cautious, I’m reading +12v between the ground strap and the positive battery terminal. This “may?“ be normal, but I don’t think so, although I’ve never checked. The ignition key is off, and no accessories are switched on.

The solenoid seems to be ok: with everything disconnected from it, the ohmmeter reflects it closing when I push the button and I have an open circuit from the solenoid case to its upper terminal. Both of these are tests indicate the solenoid is good, but I do have a new solenoid coming anyways.

My thought is to test run a (fused) jumper wire from the positive battery to ground, but if someone could run out to their garage with a voltmeter, disconnect the (+) battery terminal and measure the potential to ground, that’d be appreciated (Assuming you have a positive ground car also). Or any other advice too! Thanks as always, Jim
 
Jim_Stevens said:
...I’m reading +12v between the ground strap and the positive battery terminal...
Click to expand...

Sounds like you have a load drawing current somewhere. An ammeter across the cable and battery post would measure the draw but you'd want to start with a pretty big ammeter as it might be a dead short.

You could also connect a headlamp bulb bridging the post and cable - a dead short will cause it to light brightly. The advantage there is that you could keep and eye on the headlamp as you disconnect stuff until you find something that when disconnected makes the lamp go out.

Suspecting the solenoid was a good guess as they can stick - but sounds like you may have eliminated that as a cause.
 
The Brown wire from the starter solenoid feeds power to the car circuits - pull it and see what that does. You can also pull the 2 fuses plus the Brown/White wire going into the voltage regulator. This will also isolate the circuits and you can connect one at a time to see if that shows voltage. Do you have an Ohmmeter or multimeter? Its easier to look for resistance. Just In case you don't have them, Advance Autowire has some great wiring diagrams:

 
Done, and potential from ground to the positive terminal indeed went to zero. I have some sort of an intermittent 30-ohm short between the brown wire and chassis. (I have a Simpson 260 VOM). More fun times ahead!
Oh, and I’m very familiar with the schematics on advance autowire, having rewired this one.
 
Now you're talking! There are a few 'hot' wires behind the gauge panel (Ammeter, light & ignition switches) - maybe one came loose. I tried very hard to do a neat wiring job there but it still ended up a rat's nest - not much room and 4 gauges in the way.

I'm using dad's old Simpson 260 - yep, fun!
 
All sorted out! No idea (theoretically or practically) why there was a voltage potential between ground and the +12V terminal, but when I tested it with a light-bulb style tester and Geo’s headlight idea, there was no light, not even dimly. So I judged it safe and all was uneventful when I connected the ground directly to the battery.

And, back to the original reason the battery was disconnected, the reason I think the starter was unreliable was that when I resprayed the block, I didn’t mask the mating surface, so there was a poor ground between the starter and the block. So I wire-brushed the mating surface, cleaned it with naphtha, and reinstalled the hi-torque starter. Fired right up. All’s well that ends well, and had a nice drive this afternoon!
 
Good call on the not grounding that would NOT be an easy one.. Glad for the happy ending because I counted the teeth on an installed ring gear once, and I found it challenging to my memory.

steve
 
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