I Got an Odd Problem

[GregL]

So I wake up to a dead battery in my '77 K20 a couple days ago. I finally stumble on the fact that the blower fan is powered up with the ignition off.
Truck has functioning original A/C. Nothing has been added to the truck or changed. Stock radio, etc. So I figure I must have a bad blower replay sticking closed. Replace the relay, same thing. Blower fan will run with key off. WTF?
Anybody come across this before?
Key off, I have power at the large red wire of the blower relay. The rest do not.
Appreciate any input.
Greg

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[Wumbo]

I'd look at the ignition switch.

 

[GregL]

I don't think the blower circuit goes through the ignition switch. Nothing else seems to have any power with the key off.

 

[Termite_Delight]

Is it plugged in to the wrong terminal in the fuse box? Should be in the "ign" side.

 

[bucket]

I'd look at the ignition switch.

I would too. Could be faulty or even simply out of adjustment. Even with a good one, you can very slowly turn the key towards ON and various items will power up at different times.

 

[GregL]

Thanks for the input guys but again, only the blower fan operates. If it was ignition related I would expect the wipers, turn signals, etc. to all function as well.
TM, thanks for the reply. But all was fine one day, next day went bad so changing terminals at the fuse box is out too.

 

[C10MixMaster]

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pull the ac fan fuse check for voltage when off.. both sides of the fuse should be cold.
if the top clip is hot you have a back feed in the a/c harness then check the a/c harness for a short.
if the bottom clip is hot you have an ignition switch or harness problem
the ignition switch has more than one terminal for acc so dont totally discount the possibility of an ignition switch

i added a a/c schematic but there isn't much that can cause your problem there

 

[GregL]

Thanks for the diagram MM. I will pull the fuse, do those checks and post nack here.
G.

 

[GregL]

Fuse removed, bottom clip is hot.

 

[highdesertrange]

first off stop buying parts until you know what's bad.


then see if there is a trouble shooting guide in one of the shop manuals posted in the reference library.

if not go to that schematic that Mix Master posted and start back tracing the fan hot from the fan back. keeping in mind that the purple wire at the fan is supposed to not be hot with the key off. also the red wire at the relay is hot al the time, so one of the other energizing wires must be hot. this is why changing the relay didn't fix the issue.

highdesertranger

 

[bucket]

Does the blower run with the key turned back to the accessory position? It should not.

 

[C10MixMaster]

Fuse removed, bottom clip is hot.

bottom clip is hot unplug the harness from the ignition switch, if it goes cold , it the switch or switch/linkage adjustment

 

[Dana W Iverson]

So I wake up to a dead battery in my '77 K20 a couple days ago. I finally stumble on the fact that the blower fan is powered up with the ignition off.
Truck has functioning original A/C. Nothing has been added to the truck or changed. Stock radio, etc. So I figure I must have a bad blower replay sticking closed. Replace the relay, same thing. Blower fan will run with key off. WTF?
Anybody come across this before?
Key off, I have power at the large red wire of the blower relay. The rest do not.
Appreciate any input.
Greg

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[Dana W Iverson]

Have you recently added like a stereo maybe or something requiring wiring, if so maybe you tapped into a constant 12 volt source accidentally, bad ground