Just turning the key to on position and #7 fuse blows.
From what I can find so far is that there are three circuits or switches on that fuse:
1-park/neutral safety switch
2-back up lamp switch
3-DRL module (though I am not sure if my 2001 has drls... never have seen them)
Any trouble shooting tips appreciappreciated, thanks.

Malted insulation more than 2\" up wires.

There it is...wiring insulation gone!
Following the repair the back up lights work again as well as starting only in park and neutral.
AND THE CRUISE CONTROL!
So even though there may not be a dedicated fuse for cruise control if #7 dash fuse is blown cruise control will not engage.

 

Grab the service manual for your truck from here. (if you don't already have one...) Wiring diagrams are in section 8W.

You apparently have a dead short somewhere. Shouldn't be *too* difficult to find.

 

Actually the park/neutral safety switch is also the backup lamp switch on automatics, the backup lamp switch in the wiring diagram is only found on manual transmissions. One of those things that throws people off. Unless it's a Canadian market truck it won't have DRLs, AFAIK US trucks never had that option.

 

Hello!
So glad I found your thread. Here's what happened to me today.
Recently added new L.E.D. backup lamp bulbs, auxiliary backup lamps under the rear bumper, and a backup camera/mirror. Backup lights were wired in parallel into existing backup lamp wiring in tail lights. Camera 12v power to reverse camera was tapped into tail light harness as well. All was fine for a few days, then started blowing fuse #7 every time shifter was put into reverse.
Started disconnecting everything "by halves" until the only thing left was fused power to an open circuit harness. Thought it was likely a wiring harness problem. Didn't want to hear that as was 42 degrees f and windy here today.
Thought I would try the Forum for a quick answer, then found your thread. As soon as I read it, I knew it had to be the switch (not much else in the circuit by then except the wiring). Disconnected the switch wire connector at the transmission, replaced the fuse, then shifted into reverse. No blown fuse! With harness still disconnected from the switch, then metered one lead to ground, other lead to each terminal, then each lead to switch case. In every test, the meter revealed both switch terminals were shorting to the switch case every time I shifted into reverse.
Replaced the backup switch. Tested same in place. Then went for the test under power. Test was a resounding success as no blown fuse!
Now tail light lamps, aux backup lamps, and backup camera all work great!
Incidentally... old aux backup lamps were Halogen. They drew 8 amps for the pair. New Harbor Freight L.E.D. backup lamps only draw 600ma for the pair. Much more light, much less power draw. That's a win-win!
So thanks again for helping me find my switch problem.