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earnies2 · 05-20-2019, **(Subject: Fan switch )**

I remembered reading someware on here about puting a switch on the fan solenoid to manually turn it on. I recall I needed to break the ground wire to a switch...after doing some testing I noticed the ground wire dosen't loose ground when the fan kicks on but the power wire loses power? So do I put the switch on the power wire?

Rawze · 05-20-2019, **(Subject: Fan switch )**

(05-20-2019 )earnies2 Wrote: I remembered reading someware on here about puting a switch on the fan solenoid to manually turn it on. I recall I needed to break the ground wire to a switch...after doing some testing I noticed the ground wire dosen't loose ground when the fan kicks on but the power wire loses power? So do I put the switch on the power wire?

Some versions of MM programming default to blocking the engine fan solenoid giving an error when the ground wire is disconnected. It was done out of popular request (and as a convenience) for those who wanted to install engine fan switch on the cheap. To test to see if you have a version of MM program that has this feature, try unplugging the engine fan solenoid and see if you get a CEL in the dash. If you get no CEL light, then your good to go using that method. Otherwise, you will have to block the code in the ECU, or use a separate Solenoid for controlling the fan.

If you do have MM programming and it throws no CEL codes, then you should be able to install a switch so that it interrupts the (ground wire only) of the engine fan solenoid for switching the fan from 'automatic' (circuit closed) to 'manual' (circuit interrupted) fan on.v The solenoid ground wire is used (instead of the +12v side) so that a fuse in the circuit is not necessary.

earnies2 · 05-22-2019, **(Subject: Fan switch )**

Thanks for the reply .when I tested the circuit both wires the red wire had 12 volts and black wire was grounded. I then probed the red wire and had the truck running with the AC on and the red wire lost 12 volts and the fan kicked on..is that normal or is my truck backwards? So if I put a switch on the hot side I would need a fuse inline ....

smorgan87 · 05-22-2019, **(Subject: Fan switch )**

They are 0v on fan solonoids. Kill the power and fan comes on. When adding a manual switch killing the power is accomplished by opening the circuit on the ground side so u dont have to have extra relays and fuses to control the fan.

earnies2 · 05-23-2019, **(Subject: Fan switch )**

Mine seems to have no power until it calls for the fan then I get 12 volts?

earnies2 · 05-23-2019, **(Subject: Fan switch )**

(05-23-2019 )earnies2 Wrote: Mine seems to have no power until it calls for the fan then I get 12 volts?

I have a 2009 prostar premium could It be possible that my truck is wired in the opposite meaning the fan turns on only when loosing voltage? If i unplug the solenoid the fan dosent kick on? That being the case i would need to switch the positive wire and put a fuse on line.

Rawze · 05-23-2019, **(Subject: Fan switch )**

(05-23-2019 )earnies2 Wrote: ...
I have a 2009 prostar premium could It be possible that my truck is wired in the opposite meaning the fan turns on only when loosing voltage? If i unplug the solenoid the fan dosent kick on? That being the case i would need to switch the positive wire and put a fuse on line.

you have a prostar. they are all the same. Unplugging power from the solenoid MAKES THE FAN COME ON.

earnies2 · 05-26-2019, **(Subject: Fan switch )**

Ok update I wired in a switch from the ground wire and the fan works as it should thanks Rawze you're the best

Satori · 08-06-2023, **(Subject: Fan switch )**

(05-23-2019 )Rawze Wrote:
(05-23-2019 )earnies2 Wrote: ...
I have a 2009 prostar premium could It be possible that my truck is wired in the opposite meaning the fan turns on only when loosing voltage? If i unplug the solenoid the fan dosent kick on? That being the case i would need to switch the positive wire and put a fuse on line.

you have a prostar. they are all the same. Unplugging power from the solenoid MAKES THE FAN COME ON.

I just put a switch in on the ground wire on the fan solenoid. Now the fan wants to run all the time. Unhooked switch wiring and put back to OEM. Fan still runs all the time.