Help chasing current draw

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Sep 17, 2006
Santa Rosa, CA
I'm draw 80 to 100 ma steadily and my battery is dying fast. So, after blowing up my first multimeter (the ARB compressor switch go knocked on and was still on when I used the leads to complete the circuit), I have a nice new multimeter.

I did all the usual things. With the meter hooked up, I disconnected everything connected straight to the battery - headlights and compressor - nothing. I went into the cab and pulled every single relay, one after another. Nothing. Assuming I have some rogue wire that's not fused, I pulled the wires from the main distribution terminal so that only the large wire going to the starter and the alternator wire are left. Still drawing 100ma. Does that make any sense? Could the starter solenoid be drawing that kind of power? Could the alternator being actually consuming power when the engine is off? It's a pain in the ass to get the starter and the alternator unhooked, which I will attempt tomorrow - but I'm hoping for some wisdom to guide me.
The computer box (timer) for my carb blower was causing a parasitic draw. Replaced diodes and caps on it and was unable to fix it. Unplugging it was the only way.
Both the hazard and the ECM are unplugged right now. The only cable connected is the starter and the alternator.
I miss wired my alternator on a different cruiser, I had, to where it had power all the time and was killing my battery. I switched it to the ignition hot side of the circuit to fix the problem. HTH
When you pull relays and fuses, if the 100ma does not go away, do you reinstall them ? Reason I ask is there could be a strange issue not yet defined. The real answer would be to pull all of them out so there is absolutely no path for current. I know it is a hassle to remember where they go but it may help to define. You never mentioned what vehicle this is and if there are aftermarket add ons.
Good point 1969fj. The reason I mentioned the hazzard switch: I had an issue where one side blinker would just come on solid with the car off. Pulled fuses and nothing would stop it except removing the battery cable. After testing and checking lots of relays and grounds I finally tracked it down to a faulty switch. I took it apart and cleaned it and all was well again.
With a DC clamp meter you'll find the problem in minutes. No need to disconnect stuf. Just clamp around a wire a read the draw.

Great idea but getting to individual wires in a harness can sometimes be invasive. I wish they made those in a micro version for confined spaces.
I disconnected the entire fuse bloc.

Can that clamp meter read down to 100 milliamperes?
That reminds me - I did take the entire fuse block off also, cleaned up all the contacts with some fine sandpaper to make them all shiny (front and back). Put in all new fuses too. Figured it couldn’t hurt so between making sure all grounds were good I had a nice clean fuse box with new fuses. I also took out the old radio and replaced it with a new one and ran homeruns for power/ACC.

So I guess I did a few other things that ultimately helped with my parasitic leak.
@workingdog you are correct. 100 ma can best be measured inline. The clamp meter to measure tiny current is a too expensive lab device.

Depends on the model and resolution. 100mA, 10mA or 1mA.
Most times I find parasitic current leaks it is bad diodes in the alternator...... or the stereo...... or the glove compartment light.
I'm beginning to suspect the alternator.
Okay, if it's the alternator - which seems very likely - what are recommendations for reliable, high output alternators?
They do. I use this one, down to 1mA resolution. Picked it up in my solar commissioning days.

AEMC Instruments

That is a nice probe. 200.00 is ok as well. If I had the cash I would buy the following as it is small and is used with an O scope. I really do not like pulling wires out of a harness just to troubleshoot so the smaller probe , the better.

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