Wiring questions...

[450Nick]

Hi all,

I've nearly finished wiring up my Tuscan (from scratch!) and would like to put a battery to it in the next couple of days to test it but I have a question about the power steering before I try it and blow myself up...

I've got a Corsa C power steering rack and whilst I may not use it just yet due to some potential issues with over-assistance, I would like to run all the wires for it so that its easy to switch on if/when I want it. I have two fat power wires coming out of the main control unit that are obviously used to power the unit, one red and one brown. Can I just confirm with someone who has wired one up before, are these 12v and ground? As brown is often supposed to be a 'live' feed. Also, does it really need wire that thick to run? I've got a 4 gauge wiring feeding my breaker box and that should be plenty to run all of the systems on the car, but I'm a little concerned at just how fat those wires are, and hence the breaker rating I'll need on its supply..

Lastly, the fuel pump. I know that conventional wisdom says that the ECU trips a fuel pump relay and this is used to switch on the pump, but would it not be simpler to just wired the fuel pump up to the switch I'm using to power the ignition components? This would mean that as soon as I turn on the coils/injectors, the pump will come on, but without the potential failure point of a relay in the middle.. Or is there some sort of reason for letting the ECU do it?

[Chassis 33]

Nick, traditional Lucas colouring is for Brown to be unfused permanent live, however on German (Bosch) cars Brown is earth, given the Opel heritage of the Corsa, I'd say Brown is earth, Red is 12v feed. Cant help with wire capacities etc sorry.

WRT the fuel pump, running a pump independent to the ECU is fine right up to the point you have a big shunt, can't kill the vehicle electrics, have a ruptured fuel line and your pump continues pumping fuel resulting in a medium to well done driver.

ETA if you really are concerned about relay reliability, wire two in parallel each with a tracer LED across the output so a) you have redundancy and b)you can tell if the fuel pump is meant to be on or that one of the relays or associated wiring has failed
Regards
Iain

Edited by Chassis 33 on Monday 25th July 09:39

[450Nick]

Chassis 33 said:

Nick, traditional Lucas colouring is for Brown to be unfused permanent live, however on German (Bosch) cars Brown is earth, given the Opel heritage of the Corsa, I'd say Brown is earth, Red is 12v feed. Cant help with wire capacities etc sorry.

WRT the fuel pump, running a pump independent to the ECU is fine right up to the point you have a big shunt, can't kill the vehicle electrics, have a ruptured fuel line and your pump continues pumping fuel resulting in a medium to well done driver.

Regards
Iain

Ah of course! I'm not sure how I didn't think of that but thanks for pointing it out. I'll run with a relay then I think!

Yes I was fairly sure that the brown was earth but just wanted to be sure. Cool, I should be able to get that lot tied up this week then.. I'm loving this car building lark, I've had to stop and down tools for several long periods of time due to job/buying a house and knocking walls out of it and then waiting endlessly on engine parts but I spent a good few hours on it this weekend and its so satisfying to take a step back and look at what I've done. Almost dreading finishing it, though I suppose I'll be rebuilding it soon after I take it on track

[TVRleigh_BBWR]

You also what to use a relay, even with a switch as most switches are not designed to have high current running though them.

[sarbec]

Nick this may be of some use http://www.mgf.ultimatemg.com/group2/common_proble...
There is some ref to wireing etc

Edited by sarbec on Monday 25th July 12:06