03'55AMG

I'm looking to throw a simple switch on the ic pump but have a question. I plan on taking a 12v switched from the fuse box with an in line fuse and a switch running to the passenger compatment. But, if I take the switched hot and splice it onto the positive wire on the IC harness, will it work like I think (when switch is on pump runs all the time with key in acc, and when switch is off, ECU controls pump activation)? Also, will the ecu think the source of the 12v in the fuse box is drawing to much power and shut it off or throw a MIL?

Hotrod-Realtor

Doesn't sound like a good idea to me. If you want to power the pump with a separate power source, then I would eliminate the factory power source.
If you power the pump with a 12 volt source at the factory source, you will be throwing 12 volts to the circuit that the ecu controls.
You could accomplish what you are trying to do with an inline diode on the stock power source, so it is possible.
Several of the guys have their pumps setup to run constantly when the key is on, which is an easy way to do it.

03'55AMG

I'm trying to make it so I do not have to run it all the time though. maybe 2 switches, one before the other so if the ecu tells the pump to turn on while it's already on it won't shove 24 volts in my pump.

Hotrod-Realtor

It doesn't work that way, you won't "shoot 24 volts". The problem I see is you will power up the stock circuit with 12 volts when you turn your switch on.
Think of electricity like flowing water. A diode is a one way check valve for electricity. If you put a diode in the stock circuit, electricity would only flow from the source to the pump when the ecu opened the circuit. When you flip your switch on, electicity would flow to the pump and the diode but the diode would not allow the electricity to go to the stock circuit.

03'55AMG

Ok now I see. So it should be as simple a wiring the switch and putting a diode closer to the ecu and shrink-wrap it up?

03'55AMG

And if the switch is on and the ecu tells the pump to acvate, could I encounter problems?

Hotrod-Realtor

I don't think so, I will let others more learned than me chime in.

Bottom line is it would be much easier to power the pump to run all the time that the engine is running. I'm a bit surprised more folks don't do this. I guess I should look at doing this myself.

03'55AMG

Was looking at diodes and do not know which on to get. Looks like their rated by amperage. How many amps would I need for a diode? I was going to assume 5 amps?

nanayaw6

Wouldn't getting a relay that supports 2 triggers get you the effect you are looking for? I forget the name of that type of relay but basically the idea is
Stock positive wire routes to input 1.
Switched 12v source goes to trigger 2. Single output from relay goes to + ve of pump.

lowprofile

+1 ^^^ A standard automotive relay would work fine.

To the OP, are you assuming that the ECU is controlling the pump through the hotside 12+? I have not tested it, but it could be recieving + voltage all the time and controlled via the ground side.

03'55AMG

I stopped ove at radioshack and bought an in line fuseholder rated to 30 amps, two 1 amp 300 volt diodes, a switch, some wiring and heatshrink tubing, and a multimeter. Doing this in a few minutes, and then if it works off to spank a GTO at 3 O'clock.

04chase

did you verify this ? wondering if just cutting the stock trigger wire for the i/c pump (is it the ground or positive ?) and just wiring to a constant ign on . imo thats the best way .

Shifter

I just wired mine to run with ign on(circuit 15). I removed the red/stripe wire from the pump connector and taped off. Installed new pin/wire into connector, and wired into fuse box at drivers side of hood. This seemed to be easiest for me.