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I've recently completed electrical mods as per the Mike Drew article  using (  I didn't have a radiator fan dash light wired up so I added a suitable cable and now have an indicator when the fans are on. both my fans switch on at the same time (aftermarket adjustable temp switch) but still via the two factory relays. Anyway that is the background.

All works as it should but when the fans are off at speed the wind milling of the fan units generates enough power to light the dash warning light dimley - usually over about 50mph the light starts to glow.

Has anyone designed a circuit to cut the dash warning light connection when the voltage on it is say less than 9v ? (a guess) so that the dash light doesn't glow when wind milling but would when running voltage is turned on via the relays.  I would think a zener diode driven circuit to disconnect the feed below 9v would be suitable.

Photo is when the fans are running showing the orange warning lamp, just because I have a photo of it.  Can't take a photo of it dim when driving



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Typical voltage drop across a diode is .7 V.

This will show up as a reduced voltage across the fan terminals.

Nevertheless if you have modern fans, new heavy gauge wire, good connections, and good relays, you should not have a problem.

i’m sure we will all be interested in your results.

Normally the diode solution was inserted because when the owner shut off the car with the fans running, but before the fans stopped spinning, they acted as generators.  This kept the engine supplied with power, independent of ignition circuit. So the engine would run on, even after the key was turned off.

Keep us posted on your results, let us know if this fixes the situation.  A temporary diode install would be very easy to do - you could do it with a couple of short wires and alligator clips.


"Some owners even have enough backfeed voltage through the circuitry to cause dieseling upon engine cut off"

One of my Panteras is currently wired with this condition.  However, it does not diesel.  It continues to run normally for a couple of seconds until the fans stop spinning.  It is a 74 and is not wired for the fan light in the speedometer.  I have grown to like the "run on" and now use it as an indicator that the car is up to temperature and the fans have been spinning.  Later this year I will be upgrading the fuse panel in the car to Pantera Electronics and will dig into the fan wiring.  At that time I will likely eliminate the run on caused by the fans.

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