Another problem with the Chevy is the engine won't stop with the ignition turned off. It even keeps going with the battery earth terminal disconnected.

 

I know it's obviously the alternator keeping it going but can't find out the cure. Anyone any ideas?

ignition switch, check the wireing from the switch or switch must be faulty

you have the wires the wrong way round on the ignition barrel. easiest thing to do would be to swap them there !

Had exactly the same on the cobra I did,deffo alternator feeding igntion!-I rewired it but for the life of me can't remember how!

What Alternator are you using?

It's the Granada Bosch one. Checked ignition switch and it's all ok. I can't work it out yet, it does seem as if the alternator is feeding the ignition, but can't work out why when I switch off the ignition that all the other things powered by the switch turn off. It's just the coil that's getting power to it still.

I've read the cure for this in the past and it involves putting a diode somewhere, but can't find anything now.

on the ignition switch there is 3 main wires for the low tension side of the ignition circuit. 1 goes to the battery positive, 1 goes to the coil positive the third wire also goes to the positive side of the coil but through a resister, which the current runs through once the key is released to the run position, thats why you can take the battery off and the engine still runs, which i think is happening to your car. All the ignition switch does when you turn it to the start position is completes the low tension ignition circuit, i think some how you must have one of the wires that go to the coil possibly the wire with the resister wired up to a perminant live on the ignition switch or a short on the wires somewhere as the fuel pump is still working which only works when the ignition is in the on position, if your using an electric fuel pump that is

Fixed it, sort of. The alternator was feeding the ignition switch through the alarm system.Had to put a cutoff switch to the coil to stop engine till I get round to sorting it properly. Trouble is the alarm is just a mass of unidentified black wires so don't know how easy it'll be to sort.