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Fuses and relay

EFI Wiring Fundamentals

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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Should be install fuses before or after relay.

Hi Stephen,

I would recommend putting the fuse before the relay, as you want the fuse to fail as close to the power source as possible.

definitely before, don't forget to fuse the trigger wire either.


Is this acceptable too?

This is whats shown on the practical club level course. And if im reading it right. The fuses are after the relay.

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Bumping this thread one more time, as Jonahtan Levy mentions, the practical club level course example puts the fuses after the relays which I found strange. Now that Zac is no longer part of the HPA team, can we get some feedback from any other HPA member?

It seems like this section of the forum is not getting much support from the HPA team with Zac being gone.

Fuses are about protecting the wiring. It is very unlikely to have a problem with a relay that would cause the main battery feed to be shorted. However if you are worried you could put a fusible link (basically a high-load slow fuse) from the battery feed.

I would not be concerned with the wiring a car as shown in the diagram. This is how many production cars are wired.

Thanks David. Yeah I was not worried about the placement of the fuses after the relays and their ability to protect the wiring. Was just wondering if maybe I was missing something in the way I've done it in the past (fuses before relays).

I know Zac and many people on this forum are extremely experienced in wiring so wanted to ask the question and see if there were any benefits to placing the fuses before vs after the relays. It sounds like the answer is, they are pretty much the same in terms of protection. Moving forward I think I will continue with placing the fuses before the relays just in case the unlikely scenario of a relay causing a battery short.

Thanks again David.

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