Can I Get a Quick Check Please?

[GregL]

Woke up to a dead battery this morning. Got a draw somewhere. Found that my HEATER/A/C fuse and my ACCESSORY fuse were both hot with key off. I don't think this is the way it should be. Can anyone here check their truck for me and see if they have juice at either one of these fuses with key off please?
1977 K20.
Appreciate the help!
Greg

You must be registered for see images attach

 

[Vbb199]

Heater/AC shouldnt be i dont think.
Accessory i imagine would be, as the 12v cig lighter sockets are live always

 

[dvdswan]

cig ltr has its own fuse. accessory should only be hot with key in run or accessory. same with htr/ac.

 

[GregL]

Thanks guys.

 

[GregL]

One more question.
Do you have power at this yellow wire for the resistor on the heater box with key off?

You must be registered for see images attach

 

[75gmck25]

One of the blower motor power wires is hot all the time, with a direct connection to the firewall junction and a separate fuse. However, the blower motor relay should determine when it actually applies power to the blower motor for the high speed. Maybe your blower motor relay (should be attached to the same plenum as the resistor you showed) is stuck and providing power at the wrong time.

 

[Matt69olds]

Do the turn signals, wipers, or anything else work with the key off that shouldn’t? If so, I’d check the ignition switch first, especially if the blower motor works in all speeds just as it would if the ignition was on.

The high blower relay SHOULD bypass the wiring inside the truck with the blower switch in the high position. Technically, the relay should fail in a way that would allow current to backfeed into the truck. I suppose it’s possible, especially if wiring for the relay has gotten hot.

 

[GregL]

Nothing else is affected. When I key off, blower will still run. If I move selector to OFF, it all turns off and will not restart until key is on again. I suspect the blower relay is sticking.

 

[SirRobyn0]

@GregL I know your asking specific questions and not what I'm about to say, so you can disregard this post if you want, but at the shop we'd disconnect the negative terminal of the battery, and hook a test light from the negative post to the terminal. If it lights the test light there is a draw. Then go to the fuse box and start pulling fuses, when you get to the circuit with the problem the test light will go out. If none of them turn the test light out then we'd start unplugging stuff that isn't fused. If the test light doesn't light when we initially hooked it up, then we'd look at the possibility of an internally shorted battery that is draining itself.

 

[GregL]

Thanks for the reply Robyn. I did that test already. Showed a 37 ma draw.

 

[SirRobyn0]

Thanks for the reply Robyn. I did that test already. Showed a 37 ma draw.

Again not trying to over step just to help. While I agree that our trucks should draw nothing, and that any key off draw is abnormal, for your reference a modern car with all the computers and electronics 50MA to 80MA is considered normal. 37MA alone should not drain your battery overnight unless the battery weak. If you have an aftermarket radio with a clock and presets it maybe some or all of that 37MA.

 

[GregL]

Replaced the blower relay. Problem solved

 

[Raider L]

Just an observation.
You know what the weird thing is? That all the years that all of us have had our trucks, we still don't know a lot about how the systems work altogether. Now, some of us know alot more than others for sure, but even they don't know everything about the entire truck. You would think as old as these trucks are and as simple as they seem, at a glance, they are complicated.
I think if any of you who work on vehicles for a living, you'd be in a much better position to have to deal with more systems over a year than some of us would over maybe a decade. It depends on how many problems each of us have with our trucks.
It's just interesting to me to see how many problems turn up over "x" period of time. And it seems that they don't overlap that much either. Some problems don't turn up but every once in awhile.

 

[SirRobyn0]

Just an observation.
You know what the weird thing is? That all the years that all of us have had our trucks, we still don't know a lot about how the systems work altogether. Now, some of us know alot more than others for sure, but even they don't know everything about the entire truck. You would think as old as these trucks are and as simple as they seem, at a glance, they are complicated.
I think if any of you who work on vehicles for a living, you'd be in a much better position to have to deal with more systems over a year than some of us would over maybe a decade. It depends on how many problems each of us have with our trucks.
It's just interesting to me to see how many problems turn up over "x" period of time. And it seems that they don't overlap that much either. Some problems don't turn up but every once in awhile.

I completely agree, and as you know I'm a mechanic and manage a shop. We don't specialize any make or model, but some how we seem to see a fair number of square bodies. Just had two at the shop last week, one is owned by a forum member, and should be done next week. Another is a new customer that just moved into the state, but I'm still learn new stuff from time to time. I think I know a lot, but I still have to ask questions occasionally, and sometimes new things just popup.

But in the OP's case I still think he has a weak battery. 37MA is just not enough to drain a battery overnight, of course there is also the possibility that at times it was drawing much more than that, just not when he was checking it. Electrical draws can definitely be tricky!