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FIA master switch vs. Coil relay

Practical Motorsport Wiring - Club Level

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Hi!

I am sure most are familiar with the FIA 6 pole master switch. On the pair number 2 of the small terminals, the two wires are Coils and +12V switched supply for said coils.

Coils are powered through a Relay.

My thinking is, it would be best if these two pins control the Coil relay logic circuit, 85 and 86.

Is there a downside I don't see to doing that? I can wire the Coil Relay 30 and 87 through the master switch pair number 2, it's just thicker wires for no reason. Unless I am missing something.

My second question is regarding engine function amp draw. I have done some research and all Injectors, Coilpacks and things like MAC valve, VVTi etc don't draw very much at all. The Fuse box terminals and Relays I have are rated for 30A. At the same time I see people running separate relays for each of the functions. Is the general consensus that 30A is enough for a 6 cyl turbo engine?

My last question is a practical one. Do you guys dedicate a fuse box spot to relay control circuit power supply? If not, where do you take the power from?

The additional 4 poles are just a way of ensuring the engine shuts off. There's a variety of ways of achieving that but disabling the power supply to the coils (or ECU) achieves that aim. I'd normally use this to provide the main power feed to the relay but I can't see a downside to using it to control the relay instead.

It's typical to break down your power distribution over perhaps 2-3 different circuits and fuse them separately. This allows a little more control over the circuits and can also aid diagnostics if a fuse blows.

In all honesty it's been a while since I've used a fuse now as we almost exclusively use and fit PDMs. However you can absolutely take the main power from the fuse box or alternatively in an application with a kill switch you can take a power feed from that.

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