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Power Distribution

Practical Motorsport Wiring - Club Level

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Discussion and questions related to the course Practical Motorsport Wiring - Club Level

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Right so I am going to start from scratch and build an entire chassis / engine loom for my 73 toyota corolla and need a few things answered hopefully.

So starting at the back for power distribution.

This is what I was planning (hopefully someone can confirm this is ok.


Battery located in boot, plan to run a littelfuse 880195400 HPDM fuse block in the boot, this will allow for a pass thru for the main power supply to starter motor and two branches. One for my amp setup and one for main power feed for fuel pump.

Is it best to run a smaller constant power supply say 14awg (fused at the battery) to a fuse block up front to take constant power off? or do most take a cable from the starter lug back into the cabin to the fuse block (again assuming constant power demands are low and 14awg in this situation would also work)

Next question is I have an isolation switch (basic for car storage) assuming I do it as planned with a separate constant power feed to the front I can just install the isolation switch before the main power cable fuse strait after the battery?

Something like this

Sorry to be a pain but is anyone able to give me some advice on this? Holding back getting fuse blocks etc on the basis of this.


What is the goal of the isolation switch, if you still have constant power drains? What needs constant power?

If I wanted isolation, I would just put the battery disconnect switch on the battery negative lead. One advantage of that, is the terminals of the switch are only at ground potential and the risk of shorting your wrench while working on them is practically non-existant. You can use the disconnect switch if you need to work on any of the hot leads.

David, thanks for your feedback. purpose of the constant power being separate from the isolation switch is for the car alarm and memory functions for electronics like stereo.

But considering your negative isolation suggestion I could run a smaller fused earth to the battery for constant power circuits and run the fuse for that up front.

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