[s_morse]

For a while now I've had a parasitic draw of 4-8A (varies whenever I measure it) on my 1992 S10 with the 4.3 TBI and 5 speed. This would discharge the battery overnight to the point where it wouldn't start, right now am just disconnecting the negative whenever I park it.

To troubleshoot I first tried pulling all the fuses and shunts in the cab fusebox one by one, but the draw didn't measurably decrease with any of them. Next tried removing the alternator and starter motor from the circuit by placing the meter between the battery positive and ring terminal (to fusible links) removed from alternator, see below photo, did not see any decrease. Note that the battery positive is also removed from the alternator so shouldn't be any path to what I believe is the 2-pin connector to the instrument cluster on the side of the alternator.

From there I saw there is an unfused connection between the battery and starter solenoid via ignition switch, so tried pulling the steering column connectors, still no change in the draw. Pulled the headlight switch connectors as well and no luck, as well as the ECM connectors although I am fairly sure those are fused so would have seen a drop when checking the fusebox. At this point I'm scratching my head what is left to check, evidently there is still something drawing current. Would appreciate if anyone has thoughts what it could be or has run into a similar problem.

I've attached a couple wiring diagrams from my Chiltons manual below, with the spots highlighted where I have pulled a connector or ring terminal to interrupt the circuit if that is helpful. Note that while the fusebox is not circled I have tried pulling all the fuses and shunts in there.

A friend of mine has an Astro van with the 4.3 Vortec which also has a big draw somewhere other than the fused circuits, so I'm wondering if this is a common GM issue but didn't see anything similar that's been resolved when I searched.

 

[Usagoal]

Have you also tried pulling any of the relays to see if the draw changed? You may have one that welded itself shut (on) and continues to power whatever it is in the circuit. Perhaps a solenoid or ac compressor clutch...or something similar that could be on when you shut the vehicle off and you wouldn't notice.

 

[s_morse]

Have you also tried pulling any of the relays to see if the draw changed? You may have one that welded itself shut (on) and continues to power whatever it is in the circuit. Perhaps a solenoid or ac compressor clutch...or something similar that could be on when you shut the vehicle off and you wouldn't notice.

Good point on the relays. I don't have AC, but pulled the blower connector from the engine bay side which did not reduce the draw. Also pulled horn relay, buzzer, and hazard flasher from near the fusebox just for the heck of it.

After looking at the much better diagrams in the sticky (which I should have looked more at to begin with) also saw the hood light was directly hooked to the battery which I thought seemed a likely culprit. Unfortunately this didn't turn out to be it. I have the rear wheel ABS module not the 4WAL module next to the brake booster but figured I would go ahead and pull those connectors just in case, which unsurprisingly didn't change anything since looks to all be on fused circuits. For now I am still looking for any other non-fused path from batt positive to ground, and just hoping a previous owner didn't hide something wired directly to a hot line ahead of the fusebox.

I also saw a line on here for a 7-pin trailer connector, but don't believe the truck was ever wired for it as I only saw 2 wires coming off the junction block.

 

[PeteD]

For a while now I've had a parasitic draw of 4-8A (varies whenever I measure it) on my 1992 S10 with the 4.3 TBI and 5 speed. This would discharge the battery overnight to the point where it wouldn't start, right now am just disconnecting the negative whenever I park it.

To troubleshoot I first tried pulling all the fuses and shunts in the cab fusebox one by one, but the draw didn't measurably decrease with any of them. Next tried removing the alternator and starter motor from the circuit by placing the meter between the battery positive and ring terminal (to fusible links) removed from alternator, see below photo, did not see any decrease. Note that the battery positive is also removed from the alternator so shouldn't be any path to what I believe is the 2-pin connector to the instrument cluster on the side of the alternator.

View attachment 371176

From there I saw there is an unfused connection between the battery and starter solenoid via ignition switch, so tried pulling the steering column connectors, still no change in the draw. Pulled the headlight switch connectors as well and no luck, as well as the ECM connectors although I am fairly sure those are fused so would have seen a drop when checking the fusebox. At this point I'm scratching my head what is left to check, evidently there is still something drawing current. Would appreciate if anyone has thoughts what it could be or has run into a similar problem.

I've attached a couple wiring diagrams from my Chiltons manual below, with the spots highlighted where I have pulled a connector or ring terminal to interrupt the circuit if that is helpful. Note that while the fusebox is not circled I have tried pulling all the fuses and shunts in there.

View attachment 371177

View attachment 371178


A friend of mine has an Astro van with the 4.3 Vortec which also has a big draw somewhere other than the fused circuits, so I'm wondering if this is a common GM issue but didn't see anything similar that's been resolved when I searched.

7+ amp is significant draw. Something is either hot to touch &/or burning bright.
GM wiring doesn't have problems other than hi resistance @ corroded grounds, unless its been monkeyed with. Happy hunting

 

[ScottyV1966]

When I had a 7 amp draw that killed the Battery every night it turned out to be the diode in the alternator.
I read that you disconnected the alternator and starter, thats how I found out my alternator was bad.
Sorry, that's all I got.

 

[ScottyV1966]

s_morse,
Try This...We hooked the ammeter to disconnected negative battery post and lead, still had 4.7 amp draw. pulled alternator wire (from Pos battery post to back of alternator) and amp draw went to 0! Finally found it!
I posted this a couple of years ago.
Good Luck,
Scott

 

[s_morse]

Thanks Scott. Maybe I'm misunderstanding your test, but wouldn't pulling the alternator wire from batt positive to alternator always give you zero current? Since you are now interrupting the circuit to everything except the starter.

I did take another look at the alternator wiring last night, and am now even more confused. Hooked the meter in line with the negative wire and terminal, disconnected the ring terminal from batt positive to alternator at the alternator, this gave pretty much zero current.

When I touched the batt positive lead to alternator alone, I now got 4.5A draw. When I touch the batt positive lead to the line with fusible links going to the cab (not connected to alternator), I also get 4.5A. When I put both ring terminals together on the alternator terminal... still 4.5A. What the heck. If there is a draw in both the alternator and the rest of the system, wouldn't that be pulling more current since you now have 2 loads in parallel? I feel like I am missing something really basic about this wiring.

On the plus side, having all the connectors pulled out kept my truck from getting stolen the other night. The thief evidently couldn't get it started and went after my neighbor's instead

 

[ScottyV1966]

Thanks Scott. Maybe I'm misunderstanding your test, but wouldn't pulling the alternator wire from batt positive to alternator always give you zero current? Since you are now interrupting the circuit to everything except the starter.

I did take another look at the alternator wiring last night, and am now even more confused. Hooked the meter in line with the negative wire and terminal, disconnected the ring terminal from batt positive to alternator at the alternator, this gave pretty much zero current.

When I touched the batt positive lead to alternator alone, I now got 4.5A draw. When I touch the batt positive lead to the line with fusible links going to the cab (not connected to alternator), I also get 4.5A. When I put both ring terminals together on the alternator terminal... still 4.5A. What the heck. If there is a draw in both the alternator and the rest of the system, wouldn't that be pulling more current since you now have 2 loads in parallel? I feel like I am missing something really basic about this wiring.

On the plus side, having all the connectors pulled out kept my truck from getting stolen the other night. The thief evidently couldn't get it started and went after my neighbor's instead

s_morse,
Yes, the More I read my post it doesn't make sense. I posted that in 2019. I can tell you that a co-worker who is an Aircraft Electrician told me how to tell if the Alternator was the draw.
I would have to find the "schematic" he drew for me. He passed last year, Lymphoma, Great Guy. Anyway, the reason the Diode fried in my Alternator was the the dual electric fans pulled too many amps on the system and the diode gave in. Originally I had a 7A Draw But I had Major issues with my Whole Harness in the cab. PO Messed up everything with a "System" that was not in the truck when my son bought it.
After I replaced the Harness with a JY harness The Draw went to 4.5A. Same as yours That's what makes me think your Diode might be fried.
I had mine "tested" at Advance Auto parts, it Tested Good, It would Charge but the Diode in the rectifier was fried and after the engine was shut off it just drained the battery.
Just found this:
Can a bad diode in an alternator drain a battery?

A bad diode in the rectifier can allow current to pass the wrong direction through the circuit, even when the engine is no longer running. It's like the tap on a water jug that has a constant trickle, eventually depleting the resource it holds inside. It's called a parasitic draw or drain.
Maybe this will help you.
I Felt as frustrated as you feel Trust Me! I was ready to pour gas on it and cook some hot dogs! Changing a wire harness in the cab was not fun, and to have the problem continue really got to me.
My Problem also started when my son had the Truck at College 90 miles away and called me to say " By the way the truck would not start the other day. Horn stopped working too, and the Efans didn't seem to be working last time I drove it". So I started from Ground zero.
When I get home from work I will search for my notes when I had this problem.
Scott

 

[PeteD]

s_morse,
Try This...We hooked the ammeter to disconnected negative battery post and lead, still had 4.7 amp draw. pulled alternator wire (from Pos battery post to back of alternator) and amp draw went to 0! Finally found it!
I posted this a couple of years ago.
Good Luck,
Scott

Geaux Figure !

s_morse,
Yes, the More I read my post it doesn't make sense. I posted that in 2019. I can tell you that a co-worker who is an Aircraft Electrician told me how to tell if the Alternator was the draw.
I would have to find the "schematic" he drew for me. He passed last year, Lymphoma, Great Guy. Anyway, the reason the Diode fried in my Alternator was the the dual electric fans pulled too many amps on the system and the diode gave in. Originally I had a 7A Draw But I had Major issues with my Whole Harness in the cab. PO Messed up everything with a "System" that was not in the truck when my son bought it.
After I replaced the Harness with a JY harness The Draw went to 4.5A. Same as yours That's what makes me think your Diode might be fried.
I had mine "tested" at Advance Auto parts, it Tested Good, It would Charge but the Diode in the rectifier was fried and after the engine was shut off it just drained the battery.
Just found this:
Can a bad diode in an alternator drain a battery?

A bad diode in the rectifier can allow current to pass the wrong direction through the circuit, even when the engine is no longer running. It's like the tap on a water jug that has a constant trickle, eventually depleting the resource it holds inside. It's called a parasitic draw or drain.
Maybe this will help you.
I Felt as frustrated as you feel Trust Me! I was ready to pour gas on it and cook some hot dogs! Changing a wire harness in the cab was not fun, and to have the problem continue really got to me.
My Problem also started when my son had the Truck at College 90 miles away and called me to say " By the way the truck would not start the other day. Horn stopped working too, and the Efans didn't seem to be working last time I drove it". So I started from Ground zero.
When I get home from work I will search for my notes when I had this problem.
Scott

Ive had to add OE alts that output 50-80 amps @ idle to every vehicle changed to adequate elect fans. The original 36 to 90 max output models won't cut it.

 

[ScottyV1966]

Geaux Figure !

Ive had to add OE alts that output 50-80 amps @ idle to every vehicle changed to adequate elect fans. The original 36 to 90 max output models won't cut it.

It took 2 years to kill Mine, and That Alt was 2 years old. I imagine an older Alternator that has 80-1000K miles on it might not have lasted that long.

 

[PeteD]

It took 2 years to kill Mine, and That Alt was 2 years old. I imagine an older Alternator that has 80-1000K miles on it might not have lasted that long.

Quality of diodes enters the picture. Alts weren't meant for max op more than a few seconds. Heat kills them.

 

[ScottyV1966]

Thanks Scott. Maybe I'm misunderstanding your test, but wouldn't pulling the alternator wire from batt positive to alternator always give you zero current? Since you are now interrupting the circuit to everything except the starter.

I did take another look at the alternator wiring last night, and am now even more confused. Hooked the meter in line with the negative wire and terminal, disconnected the ring terminal from batt positive to alternator at the alternator, this gave pretty much zero current.

When I touched the batt positive lead to alternator alone, I now got 4.5A draw. When I touch the batt positive lead to the line with fusible links going to the cab (not connected to alternator), I also get 4.5A. When I put both ring terminals together on the alternator terminal... still 4.5A. What the heck. If there is a draw in both the alternator and the rest of the system, wouldn't that be pulling more current since you now have 2 loads in parallel? I feel like I am missing something really basic about this wiring.

On the plus side, having all the connectors pulled out kept my truck from getting stolen the other night. The thief evidently couldn't get it started and went after my neighbor's instead

S_Morse, did you figure anything out on the drain?

 

[s_morse]

Haven't had much time to look at the truck this week, but will definitely keep this thread updated if I figure it out. Am tempted just to replace alternator but would like to identify why the cab circuit seems to be draining, even with the alternator disconnected

 

[PeteD]

Haven't had much time to look at the truck this week, but will definitely keep this thread updated if I figure it out. Am tempted just to replace alternator but would like to identify why the cab circuit seems to be draining, even with the alternator disconnected

If alternator totally unhooked and batt still shows abnormal drain, alternator isn't primary culprit.
More like some obnoxious relay,/switch is gremlin you seek to expunge.

 

[Usagoal]

To troubleshoot I first tried pulling all the fuses and shunts in the cab fusebox one by one, but the draw didn't measurably decrease with any of them.

Stupid question: Does the 92' have a fuse/relay box under the dash AND in the engine compartment? Just wondering if ALL the fuses and relays were removed or if some were missed?

 

[s_morse]

Stupid question: Does the 92' have a fuse/relay box under the dash AND in the engine compartment? Just wondering if ALL the fuses and relays were removed or if some were missed?

No underhood box, but there is a relay hanging out near the brake booster, and one through-bulkhead connector to the blower fan relay. Unplugged both.

I had some time to look at it again today, and the draw seems to have gone down to 30mA or so. I started plugging stuff back in and checking draws, and had a false alarm when I plugged in the ignition switch, but turns out I just had accidentally bumped the key switch to "run" while under the dash.

Will keep on disconnecting the battery when parking, but will be checking the draw regularly to see if the problem rears its head again.