Earth/Positive switched Relays ??

[melhookv12]

Just looking at re-wiring my race car and was wondering which option is best. I'm sure when I worked at Jaguar they used some earth switched circuits.

Opinions and options. Pluses and minuses Please !!

I don't have much to power.

Electric Fans
Electric water Pump
Gauges
2x Fuel pumps
ECU and MSD ignition
ECU relates relays ( x3 )
2 lambda sensors

Thanks for reading.

[melhookv12]

Penelope Stopit said:

It is of the greatest importance that the relays switch the positives to all the circuits that you have listed, if you switch the negatives you will have problems

Example

If a fuel pump was permanently supplied with a positive and the relay switched the negative, should the negative wire to the fuel pump short to earth, the fuel pump would run all the time

If a fuel pump was permanently supplied with a negative and the relay switched the positive, should the positive wire to the fuel pump short to earth, the fuel pump fuse would blow

The above is only used as an example and going on the vehicle being of negative earth

As far as ECU switching goes.....The ECU would normally be activated from a relay switched positive and then do its positive and negative output switching as written to do

Switch the positives and you will get a satisfactory result

Switch the negatives and you have created possible problems

The car has a battery cut off key so circuits are only energised when in use. All other times the key is off and no power going to ancillaries.