Wiring

[Mecatech]

Hi, I am rebuilding a wiring harness for an ex BTCC Primera.

Is there any reason why I shouldn't eliminate relays for the fuel pumps, radiator fan, wipers, etc. by using switches rated for enough current in each circuit?

The switch panel is very close to the battery and fuse box so I thought that by eliminating the relays the resulting harness would be simpler and maybe even lighter. Thanks!

[brown dog]

Originally Posted by Mecatech

Hi, I am rebuilding a wiring harness for an ex BTCC Primera.

Is there any reason why I shouldn't eliminate relays for the fuel pumps, radiator fan, wipers, etc. by using switches rated for enough current in each circuit?

The switch panel is very close to the battery and fuse box so I thought that by eliminating the relays the resulting harness would be simpler and maybe even lighter. Thanks!

no reason why you can't eliminate these relays. Sometimes a fuel pump relay is wired to the ECU so that the fuel pump will only run if the engine is running, that is a safety feature, and required by the FIA in many international classes. There is no valid reason why headlights, wipers etc. need to be run through relays, as long as the switches are rated to carry the current, and you are already aware of this anyway.
I have made a lot of race car wiring looms (several hundred over the years) and the simpler you can make them, the better in my opinion. Less is more.

[Mecatech]

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[Mecatech]

Just what I wanted to hear from the right guy, thanks!

[Rubinho]

Originally Posted by Mecatech

The switch panel is very close to the battery and fuse box so I thought that by eliminating the relays the resulting harness would be simpler and maybe even lighter. Thanks!

It may be simpler but I doubt lighter as you'll be using longer lengths of heavier, high current wire in place of the lighter low current wire driving the switches. The switches will be heavier and more expensive too. There's a danger that a dirty great switch will "bounce" causing power fluctuations which is much less likely to happen with a small switch and relay. All this said, your loom will be simpler and easier to debug and provided the circuits aren't mission critical the benefits might outweigh the potential pitfalls.

[JimW]

I would just ask myself why a professional team would go to the "trouble" of using relays if they were not a "better" solution?

Regards

Jim

[Rubinho]

Originally Posted by JimW

I would just ask myself why a professional team would go to the "trouble" of using relays if they were not a "better" solution

They are a more reliable and technically better solution which is why professional race teams do use them. The OP is talking about rewiring a car himself and for it to be reliable enough and easy to maintain. Provided the OP is aware of the potential issues with this solution and is happy with the trade offs then his approach is valid.

The really professional outfits are using solid state power control systems instead of pop-out fuses and relays now. These bring huge benefits over old high current wiring methods including intelligent control of individual circuits, automatic retrying of tripped (failed) currents and interfacing with data loggers. The solutions are cost effective too as pop-outs and motorsport relays are expensive to buy and time consuming to put together.

[Mecatech]

Originally Posted by Rubinho

They are a more reliable and technically better solution which is why professional race teams do use them. The OP is talking about rewiring a car himself and for it to be reliable enough and easy to maintain. Provided the OP is aware of the potential issues with this solution and is happy with the trade offs then his approach is valid.

The really professional outfits are using solid state power control systems instead of pop-out fuses and relays now. These bring huge benefits over old high current wiring methods including intelligent control of individual circuits, automatic retrying of tripped (failed) currents and interfacing with data loggers. The solutions are cost effective too as pop-outs and motorsport relays are expensive to buy and time consuming to put together.

+ logic gates to do all kinds of interesting stuff. I wish I could have used one of those ($)