I just replaced my blower motor in my 89. The old motor seemed to be weak and when I went to disconnect the plug it was almost to hot to touch (the ac had been running while I worked on other stuff). I replaced the motor today. There was no improvement in the volume of air and the connector and wire still get hot. Voltage on high is battery voltage (12.35). Resistance through the motor shows .5 ohms. Would a bad ground cause this. I would think that for that portion of the wire to heat up, the problem would have to be at the motor. Any advice is welcomed and appreciated.

 

Sounds like the connector isn't making a good connection, resistance in the connector will cause increase in current flow with only a small voltage drop across the connector. I recently had to replace connector and relay on my Jeep because of this. Connector got so hot it started to melt.

 

The wires going to the motor and the connector have high resistance. This is what causes them to get hot while running. If you check your fuse panel under the dash you may note that the fuse labeled heater is rather warm as well. I highly recommend the blower motor to relay upgrade which can be found in the first gen sticky section. It basically is a guide to help you install a relay(s) in between the factory wiring and add a straight power source from your battery to the relay. A quick way to notice the difference in blower performance is to find the wire at the blower plug that is hot(test light hooked to ground) with the blower connector unplugged and then once you have isolated which one is the hot wire proceed by running a jumper wire to your positive battery terminal. The blower will spin much faster and you will notice good airflow from the vents. This is just a test that I use to determine how poor the factory wiring condition is. Get used to the wiring issues because your 89 will always be giving fits with something. Lol, I don't think I have five foot of stock wiring left on mine.

 

Here ya go!!

https://www.dieseltruckresource.com/forums/showthread.php?t=158400[/URL]

 

To get my 93 D350 so the wiring doesn't heat up and fail periodically, as well as make things work better.
Headlights 2 relays and 2 breakers
Marker and tail 1 relay and 1 fuse
Heater 4 relays and 1 fuse
trailer lighting and power 5 relays, 4 fuses. (1 is a marker wink relay)
Gauge pod lights 1 amp and 1 fuse
Auxiliary appliances (CB, etc) 2 fuses

you get the point. these things are wired like 1950's house trailers.