So I've managed to get the blower motor out of my jeep, and while I'm gonna try to salvage the seemingly spent motor (more about this in a different question), the voltage being sent to the motor seems to be... odd.

I connected my multimeter to the terminals that connect to the motor and went through the 4-speed settings. the voltage (it fluctuated a little) seemed to stay the same except for one setting, and I have no idea if I'm measuring this right. (I'm at school atm so when I get home I'll edit this post with the photos showing the data I gathered.)

any help is greatly appreciated.

extra vehicle notes: vehicle was abandoned for 6 years and has loads of issues, due to some abuse from a previous owner.

the engine's fixed (for the most part), just focusing on interior issues while my father's away. I work on the big stuff with him, so I don't accidentally kill myself if I do something stupid.

I'm currently trying to save myself a couple of bucks and restore the motor instead of replacing it and while I have worked on engines in games (yes ik virtual isn't the same, but it has helped A TON with the jeep) and a little bit IRL, I know the basics, and the advanced stuff to an extent I still am new to this stuff and don't know a whole lot. so feel free to elaborate on stuff. it helps :)

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    I'd suggest looking at the fan speed switch to ensure all 4 positions are working properly. TJs are known for losing speeds, or operating at odd speeds due to this switch. Commented Apr 20, 2022 at 16:01
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    @Mr.Anderson i've looked at this to an extent, during my live stream today I am gonna dig deeper into it and i'll update y'all with the results of that. Commented Apr 20, 2022 at 16:07

1 Answer 1


What you're seeing is normal for most non-electronically controlled fan motors. Those are a different story.

How these work is to have the circuit from the +12V line through a switch that then connects to a set of resistors that are used to slow down the motor. In electronics terms these are "dropping" resistors and they work following Ohm's Law that says the voltage across a resistor is the current * resistance.

For the MAX speed position there is no resistor and so the entire 12V is across the motor and it runs at full speed. For low speed position there is some resistor value that drops the voltage so that the motor runs at the lowest speed the designers want.

For all other positions the resistor value is somewhere between these two values.

To test you need to have the circuit loaded. Normally the motor provides the load but you have removed the load and so there is ZERO current (i.e. Amps) flowing. That means the voltage drop across the resistor is 0V and you will read the full 12V at the motor leads.

  • so basically no matter what it's gonna be 12v with the motor removed? and would it still provide load if it doesn't spin? Commented Apr 20, 2022 at 17:41
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    That depends on why it's not spinning.
    – jwh20
    Commented Apr 20, 2022 at 18:11
  • ok well i'll check it out when i go live tonight. @jwh20 Commented Apr 20, 2022 at 18:41
  • Could possibly put a 12v bulb as a load to check if the bulb dims at the low setting.
    – HandyHowie
    Commented Apr 21, 2022 at 8:50
  • ok, i'll try that @HandyHowie Commented Apr 21, 2022 at 13:18

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