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My engine won’t switch off!

racerdaveracerdaveMember
I turn the key to off and remove it and the engine keeps running. I had to disconnect the battery to stop the motor. But I’m not so sure the ignition switch is the problem. Here’s why, I switched the key off and disconnect the battery, the engine stopped and the cooling fans stopped too. That part makes sense. But here’s the strange part, I immediately reconnected the battery and the fans did not come back on. If the switch was shorting, I would have expected the fans to run again when the battery was connected. Of course by the time I got ready to do some serious trouble shooting, everything had cooled off and the engine started and stopped just fine. BTW, I didn’t have any problems starting the engine and the key seems to turn freely. I only mention the fans because they should have come on when I reconnected the battery if the ignition switch was shorted. Any ideas fellow Pantera owners? Has someone else had this happen?
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# #1371 (Guest)
quote:
Originally posted by Cowboy from Hell:
Dave,

This is almost certainly the ignition run-on problem caused by the way DeTomaso wired power to the fans. If so, it is a common Pantera malady.

Is your fan & ignition wiring stock? Do you have the diodes mod installed in your fan wiring?

cowboy from hell


Tell us more,I have the same trouble to ( the engine just keep running and i thought it was the hazard swith....and replaced it..but no)
and my wiring is stock. / Per
racerdaveracerdaveMember
I've got some higher output fan motors and I think I installed some heavier guage wire too. Themostats in the radiator control relays that switch on the fans. I did that upgrade 20 years ago so my memory is a little fuzzy on the details. I never had a problem until last night. And this isn't just a "run on" deal where the engine runs for a few seconds with the key off. The engine runs strong, with no hesitation. I could drive the car with the key in the off position if it wasn't for the steering lock. So what about theses diodes? Where do they go? How many ampere?
garth66garth66"When speed is the only thing that counts"
quote:
this isn't just a "run on" deal where the engine runs for a few seconds with the key off. The engine runs strong, with no hesitation. I could drive the car with the key in the off position if it wasn't for the steering lock.

Sounds like your ignition switch may be malfunctioning. Have you removed the electrical portion of the switch and rebuilt it? I think that would be a good place to start. See the first half of this article for details:
http://www.panteraplace.com/page125.htm

Here's a pic of the inside of my switch before being rebuilt, and ultimately replaced. Notice how scorched the contacts are. However, they don't need to be re-plated as suggested in the article above. The disc is solid copper and can be polished.

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racerdaveracerdaveMember
Good information garth66! Any more details on "FIX #3"? How do I identify the ACC buss from the RUN buss?
After doing a site search on fan diodes I see some issues with MSD ignitions that have a similar problem. I don’t have a MSD, but I do have a Malloy Uni-Lite distributor and I recently changed the wiring. I had it connected wrong. I had the main power wire getting power after the ballast resistor. Now I have power for the Mallory connected straight to the ignition switch. The ballast resistor is still used, but only for the coil side of the circuit. Maybe the voltage drop across the ballast resistor was enough to prevent this fan run-on issue for all these years. Or maybe it is just a bad ignition switch. But I would appreciate more details on FIX #3 if you have them. THANKS.
garth66garth66"When speed is the only thing that counts"
quote:
How do I identify the ACC buss from the RUN buss?

Check out SOBill's wiring diagrams on Pantera place: http://www.panteraplace.com/page107.htm

There's a diagram for the "Ignition Switch Accessories Bus" as well as downloadable full-sized wiring diagrams for your car which will identify the various wires coming out of your switch. Here's what it looks like for the late pre-L.

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