My 93 pickup keeps frying the reverse light switch. Gone through two switches and I'm not about to buy a third one until I figure this out. The switches last about 2-3 weeks then seem to melt between the terminals. Lights work fine with a jumper wire in the switch plug. I have not left the jumper wire in any longer than one minute, jumper does not seem to get hot. Harness between tail lights and cab look fine. All fuses are good. Bulbs good. Plug is clean. Only other electrical issue with the truck is the vehicle speed sensor does not work but sometimes the speedometer jumps all over the board, rolling or not. I'm not sure if the reverse light switch and the vss issues are related. Going to open up the harness between the Trans and the engine bay on sunday. Any input or ideas would be appreciated. Thanks!

 

Most likely cause would be a short on the side going to the back-up lights. That harness, at least on my first-gen 4runner, is poorly secured and vibrates against the tranny.
Next likely IMHO contamination from oil and dirt down there.

 

If it is a short why does the circuit protection open before the switch melts??

I guess the Op did not like my questions on his first thread.

 

Running any extra lights off that circuit?

 

In could be "mild"short", some leakage to ground, not enough to blow the fuse, OR overload condition like Robb mentions above - Enough to overload the switch but not enough to blow the fuse.

 

Could very well be poor quality switches .

Then running extra load should draw more current causing things to open.

Then the OP`s idea of a melted switch and mine may be slightly different.

 

There is a utility trailer light kit wired into the tail lights. The first switch blew before the instal and is not spliced into the reverse circut. I'm ripping the harness open on Sunday

 

There replacement switches that have blown are Taiwan SMP intermotor from NAPA. I had to return the first one I bought because the threads weren't cut properly

Here's a pic of the (melted) switch. Not totaly melted but bubbled plastic out the back.

 

The switches are of poor quality. Good point!

 

Seems to be a combination of a bad switch and shorting out. Looks to me like the switches leak gear oil through the terminal posts, in return end up shorting out the switch. Does that sound logical? I'll be getting a switch from toyota soon and post an update. Thanks everyone for the imput!

 

If that is indeed the case I would be shopping for a transfer case as well.

For gear oil to be conductive it would need lots of metal particles in suspension.

I will be looking forward to how this works for you

 

Yes, combination of contaminants, including dust could become conductive like I said above.