1988 K3500 Heater / 4 Wheel Drive Issue

[DJ1988]

I have an 88 K3500. Recently the heater system completely went out ( blown fuse ). I replaced the fuse and it blew also, the blower motor had been really noisy for when it was cold for years. I figured it finally failed. I replaced the motor and the fuse kept blowing. After much research and head scratching I finally figured out that the black ground wire coming off of the conveniece center gets hot before blowing the fuse. This wire is paired with a brown wire they both are connected to the heater circuit. The circuit diagrams show them going to the four wheel drive switch. Any suggestions other than tearing out the floor mat and tracing all of the wires? Thanks

 

[Snoots]

Question,
Does the 4WD switch work?

 

[DJ1988]

To tell you the truth I'm not sure. It's been a cold snowy winter here in the Northwest. The truck was stored outside at the beginning of winter, I decided to relocate it. That's when the heater problem showed up. I think I recall putting it 4 wheel to get out of the icy driveway and it worked. That was 6 weeks ago, I've just been tinkering with it since it was inside and I didn't have any other projects. After replacing the blower motor and the fuse still failing things got complicated. I was hoping someone here would have good advice.