Main relay..do I need it?
 

OK..it may sound like a silly question but since I am NOT Satch...heh..I gotta ASK!

I am going to wire up a 302 carbed engine separately from the Harness,BUT use the ignition switch obviously to get power to start and run.
Exactly what does the Main Relay do..or is it needed to operate the other wired circuits.

Really the only reason why I am asking this is that I have removed it(unclipped and moved the harness around..NO I did not take it out..lol!) to paint the bay and wonder if I should put the Main Relay back in!

Thanks If I can get any info on this.
Cheers STYX.

Constant voltage is provided to the relay via the EGI fuse(s). The relay takes this voltage and passes it onto the coils, injectors, ECU and various solenoids w/key to on/start. If the relay did not exist then constant power would be provided to these circuits constantly w/key to off. The question is will this drain the battery. Chances are it will, but it could always be tested to see if it does just that.

So,if I got this right the Injection system fuses would now not get power..so half the fuse block would be sort of inoperable?
Meh..no sweat to toss it back in.That way I can use the fuse block to power other stuff.

Not much help
 

I thought the standard answer on this board is 'Rip that Sh*t Out! You don't need it! You'll save xx pounds which is like FREEE HP!!!! :ylsuper:"


That didn't really help, did it?

:blush:

However, how bout that old school V8! Power to the people!

HAHAHAHA!!!!!..

Ya...feel the unleashed power when you take that 6 ounce part off the car!!!
I swear after it was removed the divided highway merged into one lane and let me take over ownership.I was King of the Interstate!
Yes..It was the ultimate Power Adder!!..I will never go back to Turbo-Charging...LOL!

Yes.

- Ted

The Main Relay only applies to EFI Systems. The fuel pump will be turned on by the Circuit opening relay, and fuel pump relay, however the ECU triggers it's opening. So unless you bridge the connectros at the ECU connector you will not have a fuel pump.

On the other hand you have a Carbie 302, therefore a mech fuel pump is likely bolted to the side of it. If that is the case you will have to modify the Fuel tank sender.

So in short...

No it will not change a thing for your configuration.

I hooked a Low Pressure electric pump to the hanger/sender assembly in the tank so I am hoping that it will get power by the key...instead of figuring out how to wire it up some other way.
This is sort of why I need to know if the relay was crucial.

I couldn't put a mechanical on without taking shit off the front of the engine as it has no do-hickey to run the pump.I checked into that before getting the Electric pump.

Ford 302 or Chevy 302?

If Chevy may I ask why not a 350+?

Get power by the key? If your going through the stock wiring, won't you have a problem with the AFM flapper switch? Or is this s5 wiring? I don't recall

Sounds like he has got rid of most of the stock wiring if he is asking about the mainrelay. Plus it is carb, so he relay has no use for the engine harness.

The Stock System uses the Main relay to power the ECU, The ECU triggers the Fuel Pump relay in concert with the ignition switch, and main opening relay. It will work, but you will need to re-wire something, what year is the base car? S4 or S5? I will dig up the wiring and figure out the quickest, simples, and proper way to do it.

1986 S4..basic jobbie..has manual windows.heh..
The sunroof is aftermarket glass so I think it was originally a hardtop version.

Ok, so On page 50-36 in the Wiring Diagram page, what you will want to do is to find your main opening relay, on S5's it is under the steering column, forward of the ignition switch on the trans tunnel side.

Then take the Brown Wire, cut and splice it to the Black wire.

What this does is it bypasses the AFM Grounding switch.
(note if you roll over your car your fuel pump will continue to run in this configuration)
You could wire an inverted safety switch here to duplicate this safety feature.

Now to simulate the the ECU is sending a signal to the relay you need to find a battery 12 V source to tie into the Black with Red wire. See attached picture for how you need to rewire the relay to work when you remove the ECU, ECU Harness, and Main relay.