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Relays to harness integration

Practical Motorsport Wiring - Club Level

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Hey Zach,

So the course does not really go into how the physical connection is made from the relays to the wiring harness/ecu.

When I look at a complete harness it is all terminated with plugs, does this mean the harness plugs into individual relays?

I don't have very much experience in automobile wiring so please excuse my ignorance.


Hopefully I can answer some of your questions.

Generally the relays are on the cabin side of the harness so the worked example really only deals with the engine harness side of the loom however Zac does mention a relay holder that he has used the GEP on which is a really nice unit that comes with the relay base and pins to terminate your harness to the bottom of the relays.

Like this one HPA posted on there facebook page.

Take a look at this video should give you some ideas around the cabin side of a fuse / relay panel.


Thanks for this Brian, in my opinion the course should have touched on this end of things in some more detail... I mean why teach the entirely process of constructing the harness and not this?

Here's an example if it helps you out, same theory applies to any fuse box you decide to go with.

Attached Files

There is a webinar that touches on body electrical circuits which is worth a watch too.


Thanks so much for the info Tony/Brian, really appreciate it!

G'day Chris.

The GEP Power Distribution Box we used in the course, and I've used in a few builds is a really good piece of gear. The relays plug directly into it, as it has standard ISO280 sizing / spacing on the pins. This means you can configure the box however you require for the number of relays and fuses you need, by re-organising the pin positions.

The reason for going this way, with a single box that the relays plug into, is that it drastically increases the simplicity of the build.

The other common way, if you're building with relays and fuses, is to use a single fuse box still, but multiple relay connecters, one for each relay you need.

I hope this answers your question? Cheers :-).

Thanks for the response Zac. The project I am working on is using a Haltech Elite 1500. The customer has the Haltech fuse box assembly....are there any downsides of using this vs switching to an aftermarket product like the GEP you used?

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