Fj60 Parasitic Draw - Something with the Alternator (1 Viewer)

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Jul 16, 2013
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Location
The Woodlands, Tx
I have a parasitic draw that I can not diagnose correctly. If the truck sits for a day or two the battery is dead. I took the negative terminal off and measured the draw between the negative terminal and the battery, its 0.4-0.5A. We pulled each fuse from the panel one at a time, and none of them changed the draw. I unplugged the fusable link, and the draw went to 0.0A. So next, I plugged the fuse back in and unplugged the alternator, and the draw stopped, 0.0A on the meter.

I replaced the alternator with an aftermarket one from Autozone. I gave the OEM to an alternator shop to see if they can rebuild it. It is still at their shop, but I have had the draw since I had a new distributor (DUI) on, and at the same time replaced the alternator.

Here are a few pictures. A few basic questions for you fellas, the fusible links should be considered good if I can get continuity between the ends? Do I have the alternator hooked up correctly? The old OEM looked like it had an external regulator, but the new alternator is internal(?) and the posts are slightly different.

Any suggestions or things to try?

batt-fusiblelinks.jpg


New Alt.jpg
 
Thank you for actually doing the first few steps yourself, can you provide more details about the truck? Do you have any electrical accessories added? Radio? Yes, the fusible links are fine if you're getting continuity over them. They're a fuse, they're either good or they're not.

Complete battery drain in a day or two is very fast.. that battery looks pretty fresh, have you had it tested? Sound like it has a dead cell.

I just installed on of those AC Delco alternators last month. The black wire is the exciter wire, the red wire is the charge lamp wire.
 
I'll argue that continuity doesn't guarantee a proper connection. When a multimeter is testing continuity, it's sending milliamps through its circuit in a closed loop to detect if current- any current - (even micro-amps) flows between its leads.
An electrical connection (like the fusible link's) can be charred and corroded and definitely not pass it's designed current, but will pass a continuity test since the test is only pushing a few milliamps through it.

But regardless of that non related info – a fusible link can't create a parasitic draw. It's just a thin wire really.

Could a bad alternator have a short in it and kill the battery? Definitely.

Since pulling the CHARGE fuse didn't kill the parasitic current draw, the short (with the new alternator) could maybe be worming its way through the CHARGE indicator bulb in the instrument panel.
Remove that bulb and see if that kills it.
The ground to the CHARGE bulb goes through a little logic gizmo. If that thing has gone belly up - maybe it's creating a circuit through the indicator bulb.
If pulling the bulb kills it - the problem may lie down stream at the gizmo.
Worth a try at least •

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CruiserMatt- I don't have any other accessories. The radio is removed and there are no other accessories, although I will tell you that there are wires from previous owner(s) that go no where. I have tried to remove wires that I could, finding both ends. The ones that I couldn't, I wrapped with electrical tape.

OSS-
Thanks for the diagram. Auto parts store tested the alternator and battery, and told be it was a bad battery. I replaced the battery last week, and it did fine for about 3-4 days, then the truck sat for 2 days, and dead when I went to start it. Should I take the alternator off and have it bench tested? Is there a way to test the diodes on the alternator, if it has an internal voltage regulator?
 
The quicker way (I think) to test @OSS idea of a charge through the charge lamp circuit would be to just unplug the connector on the alternator. I believe it should self-excite if revved over 2K rpms when the engine is first started.
 
I had this intermittent issue with a dead battery, and it wound up being the alternator. I have had several 'rebuilt' alternators go belly up in a very short time, all of them with failed diodes. So the next one I replace will have a 150A 3 phase rectifier mounted to the fender to stop this nonsense - I'll just run 10Ga wires from the field coils to the rectifier, then the only thing that can wear out are bearings and bushings!

Love the aftermarket plumber's tape battery hold down! :)

But I digress.
What year is the truck?
Was your old alternator externally regulated?
When you pulled the wire from the Alternator and the current went to 0, was it the the large one with the nut or the green/black connector?
I don't think an indicator lamp would kill a good battery in 2 days - it's .5A a 82AH (guessing 600/7.25=82Ah) battery will run that for 160 hours or so.
 
Rickyrockrat-
The FJ60 is an 86. I believe the old alternator had an external voltage regulator. The current draw goes to 0.0 when then large nut is removed. I found it a bit strange too that current doest not go back to 0.3-0.4A until that nut is pretty tight. I tried just touching the lead to the post, and there was no current flow, but once I get it tight with a wrench, then the current flows again.
 

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