88 B350 need help troublshooting heater problem

11-07-2010, 09:19 PM
My heater blower motor quit working so I tested the motor directly hooked to the battery and it works.

Now, something strange is happening when I check the voltage in the wiring coming to the motor. For example, it will read @ 12 volts, then I plug the wiring harness in (it has 2 wires - live and ground) hoping the motor with run, I get nothing. When I unplug the harness, and test the voltage again, it is now down to only a couple volts.

If I shut the key off and then turn it on again and recheck voltage, sometimes it registers @ 12 volts, but I've seen anything from 2 - 8 volts (i.e all over the map). My switch is good, but not sure about the resistor assembly or the blower motor relay. Please help me to troubleshoot this! I know where the resistor assembly is, but not sure about the relay.


11-07-2010, 10:59 PM
sounds like a resistor not uncommon for dodge

11-07-2010, 11:09 PM
thanks for the reply

Is there a way to troubleshoot this so I know for sure it's the resistor that is faulty, and not the relay or something else?


11-08-2010, 09:42 AM
The relay is only for high speed. If you're having these issues with the slower speeds then it's the resistor. Also, the reason for the varying voltage readings is the result of bad connection within the resistor.

11-08-2010, 11:42 AM
Thanks for the reply, yes it does sound like the resistor.

Even if the resistor is bad, should the high speed still work? I get nothing at any speed. If I don't get anything at high speed, does that mean my relay is bad as well?
I'd like to know how to find the relay in any case, would be much appreciated if someone could explain how to locate it.

Also, I read this in a post for a different vehicle:

"You might want to jump the tan/black wire on pin 6 of the resistor block plug to ground with the ignition 'on', the control 'on', and the blower requested, and then listen for the blower motor to run or not. If not then that motor is bad".

Any thoughts as to this method of troubleshooting. I'd like to try this on my vehicle as well, but not sure which plug to ground. Any idea?


11-08-2010, 02:19 PM
Even if the resistor is bad, should the high speed still work?

No because the high speed circuit still passes through the resistor assembly, it just doesn't pass through one of the resistive coils.

11-08-2010, 02:43 PM
I bypassed the resistor completely and I still get the problems with variable voltages, and still the motor doesn't work. I've checked connections to switches and all connectors I could gain access to.

Someone at the dealership suggested it might be the ignition switch that is the problem. This is an old van that is not worth much so I don't want to put a lot of work/money into an expensive fix like that just for the heater.
I am wondering if I could somehow bypass the wiring from the ignition switch to get power. Perhaps I could find a wire in the fuse box that only has power when the ignition is on .
If there is a better way to do this, I would appreciate a detailed explanation of how.

thanks again,

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