Just been out for a spin, got reg no. today!

Anyway, got back and found a problem ive never noticed before. If I switch the battery cut off switch while the engine is running it does cut the engine, or anything else!

Obviously the car is running on the alternator. But not sure why.

The alternator feed goes straight to the starter which has a wire going to the battery + terminal. There is another wire going to the cutoff switch and the other side of the cut off switch goes to the + feed on the loom, which powers all the cars electrics.

How is the car getting feed for the spark if the + wire is disconnected.

I will double check my wiring tomorrow when its light, I may have wired the starter motor to the other side of the cutoff meaning the alternator would be feeding the whole loom.

Any ideas incase I did wire it up right!

the FIA switches have a resistor that goes to earth and cuts engine,without it the alternator will keep ignition going.....not very good for yr alternator

Agreed - you risk doing nasties to your alternator like that unless you have the 'deluxe' cut off switch which grounds it out safely

Wonder if you could link the Battery cut off switch to the live wire to the coil though to turn it into the Deluxe version?

Although it would probably need some kind of auxilary contact or a spare one on the switch itself.

CBS stock an FIA approved one for £20

Hi the resistor has nothing to do with the actual cutting out it just absorbs the live feed that is still supplied by the altenator for the short moment after you have switched the engine of using the cut off switch it self.

cheers matt

Just to add, the FIA cutoff switch is 3 switches in one. The first is the heavy duty battery cutoff, the second is the feed to the coil, and the third grounds the alternator through a large resistor.

Cheers for the replies.

So its the earthing of the alternator that stops the engine running off it?

Im guessing that the FIA switch is the one of the left?

I've got one like the one on the right and I do believe the alternator is now buggered. When I got home in the Indy the other day tried to start it again to maneuver it on the driveway and the battery was dead. Havent had chance to properly look over it though, but it ties in with me cutting it off using the cut off switch and it carrying on running.