CUCV Headlight Battery Drain

[79Vette]

Hopefully this is a quick question for the CUCV electrical experts.

I have a 240 mA current draw on the 12V battery connection with the key off. With the 30A headlight fuse removed that is reduced to 35 mA, which is about what I would expect for a CUCV. I have reviewed the TMs and both of Warthog's excellent posts on the headlight system and fuse panel:

CUCV Headlight Circuit Explained

The headlight circuit causes many problems for most CUCV users. The GM design could use some improvements as the Headlight Fuse actually provides power for multiple circuits. We will cover those shortly. Let's look at the headlights them self first. Whenever troubleshooting any electrical...

www.steelsoldiers.com

CUCV Fuse Box Layout

There are some errors in the TM diagram for the CUCV fusebox. I will attempt to point them out as I find them Here is a "clean" fuse box with all the proper fuses and labels ITEM 2 - Hazard Flasher 3 - not used except for the M1010. The M1010 uses it for Ambulance Accessories 4 - no...

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The full 240 mA load remains with the 30A headlight fuse in place and the 15A horn (#11) and 20A courtesy lamp (#16) fused removed. See Warthog's diagram attached for number references. Physically unplugging the headlight switch with the 30A fuse in place also still has the full 240 mA load. Setting the blackout switch to the center position ("all off") reduces the load to 35 mA, just like pulling the headlight fuse

This is my understanding of the headlight electrical circuit from reviewing the TM:

• 12v power is from the battery is supplied by 8 RED-2A to ENG WRG HARNESS BLOCK. Disconnecting this at the battery eliminates the current draw (obviously)
• Power is fed from engine bay 12v block to the fuse panel in the dash by 3 RED-2G. Disconnecting this wire at the engine bay 12v block also eliminates the draw (again by stopping all 12V power to the fuse panel)
• Internal connections inside the fuse block jump power from the 30A headlight fuse (#7) to the 15A horn (#11) and 20A courtesy lamp (#16) fuses. Disconnecting either of these downstream fuses has no effect, indicating the problem circuit is fed directly by the #7 headlight fuse
• Turning the blackout light switch to "all off" or pulling the 30A #7 fuse eliminates the draw, reducing key-off battery load back down to 35 mA

Does anyone have suggestions on what I can try next? I am not sure how to narrow down the problem from here.

 

[79Vette]

Ok. I'm officially an idiot. Right after posting this I figured it out. And based on the TMs I think the phantom drain problem I was having (drain on the headlight fuse with the headlight switch plug disconnected) is impossible with a factory electrical system. Hence my confusion...

After an hour and a half of pulling fuses and looking for something wrong with the factory wiring I found the problem.

Disconnecting the harness from my homemade center console solved the problem. I noticed the issue when I installed new batteries (cable sparked when connected) and was troubleshooting with the battery disconnected to reduce risk of an accidental short causing damage/injury (pull fuse/connection/etc, check with ammeter between +12 battery terminal and disconnected cable to see if the load is still there, repeat). So consequently I didn't notice the console lights had been left on since the battery was unhooked whenever I was in the truck disconnecting things and pulling fuses.

In my infinite wisdom (lol), years ago I took power for the console lights off the back of the blackout switch so that they wouldn't come on if the truck was in "blackout mode". You know, in case I'm running from the mall cops and need to stealthily get a snack out of the console or something.

So there you have it. Another point for CUCVRUS. If you just want a reliable vehicle leave the truck stock, maintain it, and enjoy it for what it is. Then if/when you do have problems the manuals and others on the forum can help you. And if you make any changes and then have problems, even years later, go back and check your old work before diving into troubleshooting on the factory systems. At least in my case 9 times out of 10 the problem is self inflicted.

Literally every issue I have had with this m1009 has been a direct result of me trying to "improve" something. These trucks are so simple and reliable that sometimes that simplicity can be inconvenient. I wanted AC, a manual transmission and a splitter box, a turbo, solar panels, USB/phone chargers, radios, a welder powered by the truck electrical system, headsets and an intercom to talk to passengers on the highway...

All that stuff is great and I'm glad I have it, but it adds complexity. I often end up chasing my tail for days to figure out what's going on when I have an issue, and sometimes replacement parts for something I got off Amazon half a decade ago are hard to find...

So I guess the moral of the story is keep it simple where you can. When you have to add new systems or parts, avoid modifying factory systems when possible. I could have put a tap from the battery with a separate fuse to switch power to my interior lights and exterior off-road light relays, but instead I directly tapped the factory light switch to run power to the relays. It works the same 99% of the time, but troubleshooting is much harder when you can't isolate the add on system from the factory system. Keep that in mind when you're making mods or doing customization!