91 S10 Blazer, 2D 4x4.

Was driving down the highway last night with the heat on and all of a sudden went dark inside. Shut the fan off, the only light on the cluster was the parking brake light. After testing the Cruise Control and Dimmer Switch with the fan on/off and various vent positions and heat settings (thinking maybe something shorted in that), determined that it was the fan speed switch that is causing it. Tested at Idle and it had no problems, only while driving. As soon as the fan is turned off, it'll come back on. Also confirmed this morning that it does the same thing with the headlights/running lights off, so I know it's not an issue with them. Previous owner mounted cheapo fogs and wired them into the high beams, so I thought there might've been some feedback through that, but I've tested that out. There is an aftermarket radio, I have no idea how it's wired though and most of the interior lights have been swapped to LED (along with most of the exterior lighting.) Radio never shut off when the dash reset though, nor did the headlights. Unsure if the ash tray light or the 4x4 lights by the shifter shut off as it was dark out and we had a ton of deer trying to cross the highway. When the dash shuts off, it turns off the fan and the cruise control.

My question is, is it possible that it's just something bad in the fan switch that I can swap out at home, or do I need to send it to someone that does one of the rebuilds? What else can I test to see what else might be affecting that switch? A buddy said it might just be a bad fuse to the blower. I'm not super mechanically inclined (yet) but I'd think if it was a fuse, everything would just be dead?

Thanks for any advice in advance.

 

With that many modifications I'd start looking into the quality of that wiring.
It's all somehow interconnected and people are sometimes unscrupulous in tapping into whatever wire they find with current on, when making modifications to the radio and such.

 

yep! It went out completely yesterday with just the service engine soon light on. I took off the AC Controls and found that the fan switch plug was loose. Made sure it was tight and it’s been working fine since. I plan on going with a headless radio and converting that spot to a switch panel, as well as adding a CB and GRMS radio, so I’ll make sure to clean up the wiring behind the dash.

 

Ok finally got around to digging through it again. Dash went out 2 weeks ago, again took out the PW, Blower Motor, and CC. Today, we hooked a lead into the power in line on the window switch and ran it to the battery. Windows and blower worked fine (Dash is pulled right now). So we're thinking there must be some sort of fuse after the fuse block, but before said items that is blown and not allowing power through. Anyone have any idea? Realistically I don't want to pull the whole dash out to find it, but that might be what I have to do...