How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Chris (aka-Moose) Your Own Question
Chris (aka-Moose)
Chris (aka-Moose), Technician
Category: Car
Satisfied Customers: 1176
Experience:  16 years of experience
Type Your Car Question Here...
Chris (aka-Moose) is online now
A new question is answered every 9 seconds

I installed a 12V fan that runs in both directions in a race

Customer Question

I installed a 12V fan that runs in both directions in a race car. Since I did that the Master switch going to to the battery will not shut the engine off. It seems to be back feeding 9.5 V to harness which is enough to keep engine running. I installed a DPST relay thinking to isolate the fan but the 9.5 V hold the relay in. Is there something I can put on that will not let a voltage below say 11V to back feed?
Submitted: 1 year ago.
Category: Car
Expert:  George H. replied 1 year ago.

Hello I will help you with your question,

If this is a race car you are running the fan (radiator fan??) full time?

You are turning the relay on with the master switch so the fan runs?

Let me know what your setup is and I can help you with a solution


Expert:  Joe Prestia replied 1 year ago.

Yes I agree, A little more info would be helpful here so somebody can help figure out what would be causing your unwanted voltage and we can get to the bottom of a solution. Do you possibly have installation instructions for the fan and the part number and manufacturer for the fan?

Customer: replied 1 year ago.
The master switch on the car is on the main lead from the battery. The fan powers through a switch on the dash only has power when # ***** the main is on and # ***** the Ignition switch is on. I have tried it with and without a relay no difference. It seems because it is a reversible fan the power is back feeding from the alternator on the engine enough to keep it running. It measures 9.5 V I can disconnect either power or ground wire and it shuts off. I need something like a one way valve to stop the feedback.
Expert:  Joe Prestia replied 1 year ago.

Still not quite able to picture how this circuit is set up but I'll hazard a suggestion. Perhaps you could install a Diode inline between the fan and its power source?