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Main Relay


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It looks like my car doesn't have a main relay for powering all the electronics including the original ECU. The original ECU has two power wires going to it - a smaller gauge (fused) and a bigger gauge (I'm yet to buzz it out and find where it leads).

The power supplies diagram in the help file recommends using a "main relay" to power the ECU. Do I absolutely have to use it? I'm wiring in the ECU and would like to re-use OE wiring where possible.

This is a twin throttle application with Thunder if it's important.

PS I don't have a problem of laying a new wire & relay to power up the ECU. The question is more if I can use the original ECU power source (I will find out if it's fused/relayed).

Thanks for your advice.

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I would certainly suggest a main relay.  When you factor in Injectors, coils, 2 x Lambdas and all the auxiliaries that need to switch on and off with the ignition key, it would be some fairly serious ignition switch to take all that load with out a relay.

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Sorry, I think if anything I've managed to confuse myself. I'll try again now that I've found what both wires are.

My original ECU had two power supplies:

- Fused battery live (18AWG)

- Ignition live that comes out of the SAM module (14-16AWG)

Question is, do I need a a dedicated relay for Thunder or can I just go with the original ignition SAM wire and in to Thunder's '+14V In'?

Thanks again.

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