Power feedback from cooling fans to ignition

[Crosley.In.AZ]

Friend is having feed back power from his cooling fans. Shut the ignition switch off, the engine runs on for few seconds, then dies.  If he pulls the fuse from the cooling fan circuit , the engine dies with ignition shut off , does not run on.

The fans are hooked to a relay , that is triggered by the ignition switch. I have not seen the truck yet.  I told him something needs to be rewired to avoid feedback, but I do not know what yet.

Or:  maybe a diode in the power circuit to the fans?  Like is used on the alternator circuit often?

[WZ JUNK]

Needs a diode.  The WZ JUNK truck has done this for 30 years.  I just never added a diode.  Sometimes I will pull up somewhere, shut the engine off, get out of the truck and walk away, then the engine shuts off.  I just thought it was kinda fun and quirky.  Someday I will fix it.

[58 Yeoman]

I hate gremlins.  I had a '46 Ford 1/2T PU that would be running fine down the road, then all of a sudden stop. Wait beside the road for a while, and it would start and run fine, sometimes for days or weeks, until it did it again. The gas tank was under the seat, and I finally took off the sending unit and looked inside. There were THREE apple seeds in there, and eventurally they would all gather at the bottom fuel outlet and plug the line. After the fuel pump pressure bled off, it would start again.

[chimp koose]

Had a friend have the same problem with errant shutting off for no apparent reason . Ended up finding a rolled up newspaper stuffed down his fuel tank (old chevy truck). It would float around and every so often cover up the fuel pick up in the tank .

[Crosley.In.AZ]

Needs a diode.  The WZ JUNK truck has done this for 30 years.  I just never added a diode.  Sometimes I will pull up somewhere, shut the engine off, get out of the truck and walk away, then the engine shuts off.  I just thought it was kinda fun and quirky.  Someday I will fix it.

thanks.  I had suggested that diode to this fellow in the trigger wire that feeds the relay.. 

I will mention the wire harness fuse block setup, he bought a $118.00 setup on eBay for the truck.  So it is very basic

[kb426]

If he changes the relay to be controlled by the ground, I believe it will eliminate the problem. The electrical experts know more about this than me. All of the modern efi ecu's only control the ground circuits on relays. The sniper on the F16 is the same way. I set up the fan controller on it to be ground controlled. I have a toggle switch that energizes the fan for "parade" mode. I use that when operating at slow speeds rather than waiting for the engine to get hot and then start. When the switch is on, it connects to ground.

[Crosley.In.AZ]

If he changes the relay to be controlled by the ground, I believe it will eliminate the problem. The electrical experts know more about this than me. All of the modern efi ecu's only control the ground circuits on relays. The sniper on the F16 is the same way. I set up the fan controller on it to be ground controlled. I have a toggle switch that energizes the fan for "parade" mode. I use that when operating at slow speeds rather than waiting for the engine to get hot and then start. When the switch is on, it connects to ground.

I agree with you. I dont know how the fan cooling  circuit is wired.. If he has a separate hot wire to the relay that does not pass thru the fuse block?

I had suggested a rewire to a grounding trigger wire if possible, not a hot feed trigger wire.  I think that blew him off the road aka confused?

[Crosley.In.AZ]

Here is what my buddy did that fixed the problem on cooling fan power feedback.

He used the same diode as often corrects alternator feedback... he installed the diode backawards on the ground wire for the cooling fans  and the engine shuts off as it should now.  Cooling fans function normal he says