I am blowing the circuit breaker on the electrical outlet when I
plug my truck in. It worked a week ago, my truck won't start (-18 last night) without being plugged in, and it blows the breaker on two different outlets. Do I have a short in the truck somewhere? I looked at the fuses and relays and everything seems to be OK there, but I'd be willing to try anything.

Stuck in Silverton, Colorado.

 

test the resistance on the cord end. Should read 20-22 ohms. 30 is still ok, but means the block heater is starting too die. If you get 0-2 ohms, then yes there is a short in the cord, and best action is too replace it. Most likely the cord end was crushed (making connection in the cord end). Thats what happened too me anyways!

 

The block heater cord doesn't go through the fuses so it won't do any good to check them.

If you have an ohm-meter check for continuity between the prongs on the block heater cord and the truck's frame/ground. If you have continuity then you have a short.

If the plug is wet and you are plugging into a GFCI protected outlet then that could be popping your GFCI outlet or breaker if it is a GFCI breaker. Where exactly is the breaker popping? At the outlet (which means it's a GFCI) or at the circuit breaker panel (which means it could be either a normal breaker or a GFCI breaker).

Make sure the extension cord stays dry. Try plugging into an outlet that isn't GFCI protected for a test. Kitchens, bathrooms, garages, and porch outlets are supposed to be GFCI protected so try somewhere else.

 

Yep the breaker is on the outlet, and popping there. I will try plugging it into a non protected outlet, but if this works what does that tell me? I need to get an Ohm meter I suppose.

 

Then you have a GFCI outlet and you most likely have a moisture problem somewhere. Dry everything out and try again. If it still pops then you could have a bad extension cord or possibly a bad block heater cord. Like ramtd02 said, check the continuity between the prongs (on both the block heater cord and the extension cord). If there is no resistance (zero) then there is a short.

 

I'll Try all of those options. Thanks

 

....and GFI outlets don't last forever either. I just replaced one in my garage that would pop too easily and wouldn't always reset.

 

I'm with J, the more a breaker trips the weaker it gets till it blows with even a small load.
Time to replace it.

 

GFI outlets don't drip because of too much current. They trip because they detect a ground problem. I've pull over 30 amps through some of mine without problem. 20 amp circuit breakers in the box start tripping at that point.

Somewhat simple explantation.
If you pull 10amps, it expects to see 10amps on the hot wire and 10amps coming back on the neutral wire. If any current comes back on the ground wire or not enough through the neutral wire it trips the GFI.
Clear as mud? Good I hope I didn't comfuse too many people.

Bio,
If it works on a nonprotected outlet it means either your GFI is junk(possible) or there is a ground to neutral problem in your wiring on the truck or extension cord (most likely).