i have a 1968 camaro with a 12.1 302.after installing a electric fan i am experencing engine run on .but only after the engine has ran for over fifteen minutes,or the rpm has been up a few times.i believe the fan motor is run the ignition system. i have tried the fan hot wire to the battery ,alt.and fuse box on acc. will a diode fix this?i already have one on my msd box .any thoughts on this would be greatly appreciated.

Is Your fan wired up through a relay?

Originally posted by 18436572:
Is Your fan wired up through a relay? Ditto

eh, i just turn the car off in drive, then shift to park.

for me, a diode fixed the problem though.. my MSD was still drawing energy after turn off

Originally posted by 18436572:
Is Your fan wired up through a relay? Ditto. Something isn't wired correctly.

I believe if you are using the MSD system and still have the three wire alt with external voltage regulator, VERY little residual voltage is required to cause "run on". You might search the archives as I did with this problem, and install a diode from Radio Shack, or even where I got mine, Advance Auto, and install it at the wire running back to the gen light on your dash...
http://www.msdignition.com/1troub1.htm#runon

Could also be that your idle is set too high. drop it down and see what occurs.