Cars House

I'm in the process of doing the blazer motor upgrade in my '83 CJ7 and have a wiring issue that I'm stumped on and can't find anything in any of the forums. The PO basically pulled the heat out, so I'm starting from scratch so I don't have any idea what everything was before I pulled everything out. He had used the electric (tan cable) running from the heater switch to the carb he put in, it wasn't giving any power unless the heater switch was on which explained why it wasn't running to great.
Once I figured that out, I hooked the new blower motor up to the switch via the tan cable running to the engine compartment but as soon as I turn the switch on, the fuse blows.
It's a 3 speed switch and I don't get anything out the motor until I'm running at high, which from browsing some threads seems to indicate the resistor is shot? But I dont think that explains why the fuse is blowing?
From the wiring diagrams I've looked out, it appears there is a ground wire running from the blower motor but there wasn't one on the motor I pulled and can't seem to find any reference to anybody running one on any of the posts on the motor swap.

Does anybody have any insights from doing any work on their Blower motor? I put in the Seimens PM102 model if that matters.
I mistakenly didn't test it before I put everything back together but I think I'll need to pull everything out again.
I am pretty sure that the motor grounds when it is attached to (touches) the firewall. No wire for ground. The firewall is the ground.
I used sealer between my motor and firewall (oopppss), so put a hose clamp around the motor housing and ran a wire to firewall.
When I did mine, I talked to the local electric motor expert and he said I had to have a rheostat switch, because that's what the chevy's came with. A regular switch has too much resistance on low/med. But I did have the old two speed motor, so I don't know if the 3 speeds are rheostat or not. The other option is to just use a toggle switch, but then it would be wide open all the time. and yes i did have to have a ground wire.
Well what size fuse blew? Maybe he had the wrong size in there. I think stock was 25 amps. Make sure the fan spins by hand though, a stalled motor current can be huge.

I havn't had any trouble with the switch when I put my motor in. Didn't have to change anything. Like you said. the resistor pack probably has a problem with a broken wire/resistor or something. Maybe even the plug is bad. I've seen them melted on the switch and the resistor pack.
The switch sends direct power to the motor on high and sends power to the resistor pack stuck in the plenum right above the fresh air vent on the passenger side for the lower speeds.

Some motors do need a ground, it won't hurt to run one just to lessen the load on the stock mesh cable that runs from the engine head to the firewall. The blower will run faster with it's own ground usually, so will the wiper.

I use a battery booster cable and clamp it on the battery negative, then go to the motor case to see if that makes a difference. If your motor is 'stealing' a ground, fuses can overheat.

I also think I would run a 25A fused wire direct to the heater blower to see if it holds or not before going crazy with the rest of the Jeep's wiring just to verify the motor, but if it is new the odds are it's something else.

Your motor's squirrel cage isn't hitting inside or anything like that? Any scraping noises? They 'do' make two sizes of shafts. Usually the more expensive motor has the wrong shaft and the cheapie has the correct one.
jp360cj - Where did you run the ground wire from on your blower? From the firewall side of the motor?

I'm going to try the ground from the motor housing on the engine side of the firewall. When I enlarged the hole for the motor it might have lost solid contact with the firewall to get a good ground.

It's a 25Amp fuse that's blowing. The fan spins by hand and I can hear it moving for a few seconds before the fuse blows. It doesn't sound like anything is getting hit. The motor is the same size post as the one I pulled, after returning the first I picked up.
I haven't checked the resistor yet but I'll check it over the next day or two.
I'll try running a fused wire direct to the blower to see what happens there to help rule anything out with the motor itself.

Thanks for the input so far, I figure I'll get heat put in the darn thing in time for the warm weather to come.
Thanks for the input so far, I figure I'll get heat put in the darn thing in time for the warm weather to come.

Hurry up, eh.
(Up in The Great White North with a broken frame waiting for 'spring' to replace it, new one is buried under snow)
jp360cj - Where did you run the ground wire from on your blower? From the firewall side of the motor?

Well, I've got the old style heater, so my blower motor is on the inside, underneath the glove box. It shouldn't matter which side it grounds from, so I'd just do whichever is easier.
Well, I've got the old style heater, so my blower motor is on the inside, underneath the glove box. It shouldn't matter which side it grounds from, so I'd just do whichever is easier.

Sorry, didn't check to see what year you had. Thanks.