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Old 09-28-2024, 01:36 PM
onewheelpeel onewheelpeel is offline
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Default How To Locate Parasitic Draw In Lighting Circuit?

I have a 79 T/A 10th Anniversary K code with an Olds 455. After removing the fuses, I still have a 1.5 amp draw across the disconnected negative battery terminal.
I disconnected the alternator and still have it. I remove a large ring terminal (which a previous owner grafted from what would have been two ring terminals) from the large stud on the starter solenoid that connects to the positive battery cable.

The drain then goes away. I also have replaced the headlight switch and see some wires have been modified behind the instrument cluster.

The car is otherwise drivable as long as the battery is disconnected each time. but also has no tail lights or brake lights though the dash lights and headlights do work as long as the ring terminal at the starter is attached, and which contains the parasitic draw. Of course the tailights and brake lights go through the fuse panel and which has good fuses and no power drain.
I'm thinking of just running a jumper wire to the tailights at this point. Tail lights and brake lights would be very helpful in staying out of trouble.

How can I track down the parasitic draw? It looks like someone previously made "repairs" to wiring behind the gauge cluster and one wire that attaches directly to the gauge cluster on the "inboard side of the cluster- or the gifts that keeps on giving!

I believe I have the circuit identified but the car wont start without those problematic ring terminals attached to the solenoid and which contain the battery drain. . Thank you.

  #2  
Old 09-28-2024, 01:45 PM
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dataway dataway is offline
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So the drain is still there if you pull the main bulkhead connector off the fuse box? (I am assuming it has one, I could be wrong).

1.5 amps would be about 20 watts at 12v, similar to typical incandescent taillight bulb.

Sounds silly, but you might want to turn out the lights and look the car over well and see if you can see any lights glowing anywhere.

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Old 09-28-2024, 08:07 PM
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Bill Hanlon Bill Hanlon is offline
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Quote:
Originally Posted by dataway View Post
Sounds silly, but you might want to turn out the lights and look the car over well and see if you can see any lights glowing anywhere.
Don't forget the glove box light, console light, trunk light and underhood light if you have them.

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Old 09-29-2024, 01:00 PM
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george kujanski george kujanski is offline
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I believe the wire you are speaking of is the main feed from the battery to everything else. Since the taillights are not working when this wire is disconnected, there is a wiring problem somewhere. Check any other mods that were done and then all of the fused circuits.

One way to check the fused circuits is to use your multimeter (i assume you have one; you measured 1,5A draw initially), pull each fuse one at a time and use the multimeter in DC amps mode with the two probes across the fuse contacts. This would indicate the current that would exist thru the fuse and may help narrow down which circuit is causing the issue.

George

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Old 10-01-2024, 08:39 PM
onewheelpeel onewheelpeel is offline
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I appreciate the replies - I have some more checks to make based on your suggestions but did see a tail light barely glowing. I also had a very light positive indicator on the tail-lite and brake light fuses when I put a test light on the tail light and then brake lite fuses. Then I disconnected the harness at the trunk connector but didn't get the faint lighting of the test. It may be that I had a bad ground on the testlight as there must be something as the tail light bulb was lighting up faintly when it was plugged in.

I wonder if the printed circuit board is a part of this. I so don't like "throwing money" at electrical problems with guesses though. I also have the voltmeter, a Klein I believe.


Last edited by onewheelpeel; 10-01-2024 at 08:42 PM. Reason: typo king
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Old 10-02-2024, 11:23 AM
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Quote:
Originally Posted by onewheelpeel View Post
It may be that I had a bad ground on the testlight as there must be something as the tail light bulb was lighting up faintly when it was plugged in.
When you use your meter in "amps mode" like George suggested you don't put one lead on ground. You remove a fuse from your fuse box, touch one lead of the meter to one of the fuse contacts and the other meter lead to the other fuse contact. I'd use the 10 amp scale that most meter have. If you don't see any current on 10 amps, then change the meter to a lower amp scale.

Caution: Inserting an ammeter into a circuit that is flowing more than the rated amperage of the meter will probably cause a fuse in the meter to blow. Most meters don't make it easy to change the fuse.

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