Electronics 2000

PS, if you want a circuit ( its a JK flipflop, a momentary switch, probably a few resistors, strip board and a transistor) I need to know the current through the low current( ignition side) side of the relay, in order to choose a suitable transistor.

If you put a multi meter set on 10A between the relay and a 12V batt and the other small terminal to the other side of the batt it will give you the amps through the switching side of the relay.

If you want the circuit tel me what that current (amperage) is.

Any problems let me know.

Tar&stuff.

I think I would recommend the circuit, because its a big relay and the current is going to flow through the ignition, you could probably find a different circuit from the fuse box, which would solve that, the ignition switch is not designed to switch such a big relay. Ignition switches and keys are expensive on modern cars.
As I said there will be lots of suitable circuits which are on when ignition is on and off when ignition is off in the fusebox.

How are you with a multi meter?

The circuit only draws power to the small power supply flipflop and transistor base, so won't hurt, still that could run from the fuse box for extra safety.

Tar&stuff.

I will take the recommend bit back.... It makes no difference if you go from the fuse box. Entirely up to you.

If the radio is off when the ignition is off you could use the same power supply, at worst you will blow a fuse.

I recommend that you do not switch that size of a relay through the ignition switch.

Tar&stuff.