My MSD electronic ignition is wired to use a relay to “switch” on and off the 12v feed from the battery. The wire used by the PO to trigger the relay developed a short and I was not able to trace it (it disappeared into the webbing of the harness). So I rewired by running a new wire from the unfused side of the #6 fuse to the relay.
The engine starts up and runs fine however now when I turn off the ignition switch there is a short hesitation (about one second) before the engine turns off. Any idea why?
It didn’t do that before so I’m wondering if I should have wired it directly to the ignition switch?
If a motor (like the fans) is running when you shut down, they can act like a generator and back feed the circuit for a short time. This might be the cause of the delay.
That’s an interesting point Bill. You are correct that the electric (radiator) fans are running when I shut off the ignition. Would you recommend that I attach the wire to a different location to avoid the delay? Considering that the voltage needed to trigger the relay is low would hooking it directly to the ignition switch be a good idea?
There’s nothing inherently wrong about the delay. It makes no difference where you connected it if can see the fans when the ignition is switched off. Now that you know what’s going on you can sleep at night… I think I would just live with it.
Why do you have a relay? Works fine off the ingnition switch, and the relay just adds a fail point.
To get rid of this problem, move the fan connection to an always-on fuse. That will isolate the fan from any switched component, including the ignition system. The fans will continue to run after shutdown until the otter switch turns them off, which you may consider an advantage.
I can understand where the fan spin down could be causing the issue, but I wonder why it would do it now when it did not do it before. Same fans, same relay, from what I understand. You may wish to first try shutting down when the fans are not running to confirm whether it is indeed the fans.
You said you wired with a new wire, is it connected to the same place as the original, or did you find a new source?
Tom
Depends on how the relay was wired before this started. If you noticed, he said that it was set up to switch the “12V feed from the battery”. Which suggests that the C’s were powered directly from the battery and only the W’s were switched. So something changed in the move to fuse 6.
Michael, you are exactly correct on how it is hooked up. Tom, I could not locate where the original wire was attached for power - it was a well worn original wire that had lost its identifying color markings and disappeared into the wiring harness. When I get a chance I’m going to remove the wire from fuse 6 and hook it directly to the ignition switch which I now think is the preferable way to do it.