the fuse was blown for the blower motor, so when I replaced it the fuse blew again as soon as I turn on the heater. looking at the wiring diagram, I believe the heater switch and the backup lights share the same ground for whatever reason, so I put it in reverse and sure enough, no lights. funny thing is, the fuse for the backup lights isn't blown. I just recently had the dash apart to do some painting,however, never did manage to get the lower dash removed just unscrewed, and I'm wondering if there is a screw or something that completes the circuit like there is on the dome light, if so, which screw should I be looking at? I looked under the hood to try and trace wiring before checking the backup light situation, all looked good from what I could tell (mind you I'm far from an electrical expert), so I believe the issue has something to do with that shared ground thing. it's cold out, i'm tired of banging my head, and this dag-gone wiring diagram gives me a headache. by the way, the truck is an 84 f150 with factory a/c, and about a month ago I replaced the blower motor and cleaned the cavity all out. the heat has worked great since then up until yesterday when I tried it to no avail. dash work was done just a couple days ago, yesterday was first cold day since. any and all suggestions would be welcome, as I'm at my wits end here, I can't even find this " shared ground" wire, hoping I don't have to disassemble the dash again to get to it.

 

A shared ground is not going to blow a fuse. A fuse will blow when the circuit is overloaded. This overload will be something like a pinched wire under a screw or something like that.

If you have another fuse, I would unplug the blower motor, replace the fuse, and then turn the switch on with the blower motor unplugged, and see if it blows. If it does, you have a wiring problem, I would guess caused by your dash work.

 

I'll give that a try, but while trying to narrow down the issue previously stated, I decided to run to the parts store to grab a handfull of fuses, when I started the truck I turned on the wipers, and now they are in the upright position and jerking a little back and forth, also my tach isn't working, all other gauges do though. I'm about to assess how much all these electrical issues are going to cost, and compare that to the cost of a cheap shotgun and some shells, and solve this one way or the other.

 

ok, I've got the wipers working again, just manually pushed them back into position. disconnected the blower motor and tried the switch, same thing. still no tach either. proceeding to disassemble the dash again to see what I can find with absolutely no clue what to look for. check back in to report soon.

 

I've got the heater working again, under the hood there are alot of wires and harnesses that aren't connected to anything compliments of the PO. when I got the truck, they were all over the place and most of them had insulation crumbling off. I've got them all taped up and out of the way, however I must've missed one because it wasn't taped and was coming into contact with something causing the short. now I just have to figure out why my tach stopped working, time to pull fuses one at a time. thanks franklin for the disconnect motor idea, that at least let me know it was along the wiring.

 

this truck has one helluva sense of humor. heater works, wipers work, tach works, now my radio doesn't work. my truck just doesn't want to see me get bored, it's nice to know that it cares that much about me, but I wouldn't mind it if it stopped keeping me "entertained". anyway, at least I got the important stuff going again.