Heater blower motor battery drain

[Raybob9289]

Question for Squarebody wiring gurus.
My 77 Cheyenne has a 7 amp battery drain. Dead battery in the morning...
I tracked it down to the fan blower motor. I installed new blower motor (original bearing was howling) and a fan resistor. Still 7amp draw with key off. Tried a different ignition switch. Why is the HVAC fuse hot when the key is off?????
Fan switch is hot when key is off??? WTF over. Anybody had this problem??

 

[Ricko1966]

Look up the wiring schematic for your truck. I believe it is supposed to have a blower relay on the firewall that has a constant hot. The relay is controlled by the heater blower switch which should be a keyed hot. I don't have every year and Air conditioned,not air conditioned vehicle memorized. But I think what I described is how your blower motor is supposed to be controlled.

 

[Raybob9289]

Thanks Ricko 1966,
I have no relay. Just hot to dash switch out to Fan motor resistor then fromthere to fan motor.

 

[Ricko1966]

Thanks Ricko 1966,
I have no relay. Just hot to dash switch out to Fan motor resistor then fromthere to fan motor.

Yea I'm pretty sure that hot is supposed to go to a relay. I'll go look under the hood of my 75. I was comfortable on the couch dammit. Yep my 75 has a blower relay under the hood. Mine is air conditioned though. Go to the top left of this page. Hit the three dashes,rap forums scroll down to Squarebody reference library,tap that,find wiring schematic for your truck. I'm sure the relay is the missing piece of this puzzle.

 

[Scottgenex]

I just so happened to be standing next to my '76. This is the relay you're speaking of, correct? Previous owner bypassed the "always on ventilation" and had the blower on a always hot switch. Took me some doing to get it back to how it was so I wouldn't leave it on and kill the battery.

 

[Raybob9289]

My 77 Cheyenne K30 is a non A/C truck that means NO relay. I lucked out last winter and scored a 1977 GM truck factory service manual with all wiring schematics (from 76) on eBay. The wiring schematics don't show a relay on non A/C truck.

 

[Ricko1966]

I can't read your schematic I looked one up it shows I believe it was four wires coming through the fire wall going to the resistor. I believe one was orange and black. Don't remember the others. Please put up a better view of your schematic. Especially the heater wiring.

 

[Scottgenex]

I cropped one I had downloaded. Has the wiring been modified and/or moved to a different lug on the fuse panel that's not ign hot? Or did this just randomly happen one day? Just curious cause of the engine swap.

 

[Raybob9289]

I cropped one I had downloaded. Has the wiring been modified and/or moved to a different lug on the fuse panel that's not ign hot? Or did this just randomly happen one day? Just curious cause of the engine swap.

Scott,
I beleive if memory is correct I put the new fan in before the LS swap and had a dead battery in the morning. I was thinking like you that maybe it's because of the LS swap. Orange wire to HVAC fuse is hot in key off position. So obviously the HVAC fuse is also hot all the time. In all my years of messing with GM wiring orange has always been hot at all times. So thats what's bumfuzzling me.

 

[83Stepper]

My 77 2wd C10 non-AC truck didn't have a blower/heater relay either. If anything, that should be a key on hot only to prevent this specific issue from occurring. Wondering if somebody at some point in time wired it in with the cigarette lighter circuit which is hot at all times and it's backfeeding the fuse causing the parasitic drain. Orange is also the color of the hot lead on that cigarette lighter circuit...just sayin. Try pulling the fuse from the cigarette circuit and test to see if you've still got that hot lead back at the fuse.

Going to pull some of my manuals and check the wiring skizmo's, but it just doesn't sound right that it's hot with key off on a non-AC truck.

 

[75gmck25]

On an A/C truck there is a wire with a 30 amp inline fuse, running from the junction block near the brake booster over to the blower motor relay on the plenum. When the blower is on high, it’s powered through that fuse, not the fuse in the fuse box. I don’t know if a non-A/C truck has that same 30 amp fuse.

 

[83Stepper]

On an A/C truck there is a wire with a 30 amp inline fuse, running from the junction block near the brake booster over to the blower motor relay on the plenum. When the blower is on high, it’s powered through that fuse, not the fuse in the fuse box. I don’t know if a non-A/C truck has that same 30 amp fuse.

My 77 2wd non-AC truck didn't have that. Believe it was A/C and the HD heater RPO's only that had that. Below is an unrefined pic of my old 77's heater box. Just the 3 leads (lt blue/brown/orange) going to the resistor and one headed to the blower motor.

You must be registered for see images attach

 

[Jgonick]

very long shot- try unplugging the brown wire at the alternator. (Field current supply) If your alternator (connected to battery) is faulty it could technically back feed into the same circuit you are dealing with. Then see if you are still getting voltage on the fan switch/HVAC etc.

 

[Ricko1966]

very long shot- try unplugging the brown wire at the alternator. (Field current supply) If your alternator (connected to battery) is faulty it could technically back feed into the same circuit you are dealing with. Then see if you are still getting voltage on the fan switch/HVAC etc.

Actually this is an excellent call. I feel stupid I didn't already suggest it.

 

[Raybob9289]

very long shot- try unplugging the brown wire at the alternator. (Field current supply) If your alternator (connected to battery) is faulty it could technically back feed into the same circuit you are dealing with. Then see if you are still getting voltage on the fan switch/HVAC etc.

Ding, Ding, Ding.... Winner Winner Chicken Dinner.
When I did the LS swap I hooked the brown alternater wire to battery power thinking it would power the gauge. Just like Jgonick said, it was back feeding the HVAC fuse. Causing the fan circuit to be hot all the time. I cut that wire didan amp draw and after te ecm went night night nothing.
Jgonick you are officially a Square body wiring Guru and I owe you a sixer...
Moochos Grassy Ass