Battery Cut Off/Shut Off Switch Questions

[haroldd1963]

A couple of questions concerning installing a battery cut off/shut off switch in my FFR MK IV Roadster.

I am running the stock Ford EEC IV Mass Air fuel injection system.

Most switches I have seen installed are on the positive side of the system. The way I was taught to dissconect a battery on a fuel injected vehicle, was to remove the negative side first, supposedly to protect the PCM from damage. Also, by shutting down power to the PCM, will it have to re-learn it's idle strategy every time power is switched on/off?

[FFRSpec72]

In racing we are required to power down the entire car, we do get an exception for the ECU, so the ECU (keep-alive) is a separate connection, but make sure you take into account alternator feedback that may keep your engine running when you kill the power.

[Desert Cobra]

Check the rules under which you will be racing. A cut off switch may have to be accessible from out side the car and/or be located in a particular place on the car. Some racing associations also require a decal identifying the switch. Check with the tech inspection people, or get specs on line. I could be wrong, but I think the switch must be on the positive side, must have a red handle and must be forward of the cabin area of the car.

[edwardb]

Normally you switch the positive side. If you have a computer or radio to keep alive, use a product like this:

http://www.speedwaymotors.com/Memory-Guard-for-Electronics,2383.html

Takes a small trickle off the battery even with the master switch off.

[Mesa Mike]

Most track cars have it on the positive side (as I do) and mounted on the rear of the car, easily visible to the track EMG people and marked "on/off" (as I do).

[avgjoe]

Like Tony said, we just run a wire around the kill switch to the KAM pin (#1 I think). I put a fuse in it and just ran it from the PCM to the hot side of the battery disconnect switch. No fancy extra "headaches" waiting to bite you and leave you stranded. Works like a champ. You are correct in that after killing power completely to the pcm it needs to relearn some stuff. A few laps around the block usually does the trick; it doesn't learn anything at WOT, FYI.