I've seen many threads about wiring the IC pump to run constantly. Some recommend a relay, others simply fuse the positive lead to a switched wire in the fuse box. I've read that the Johnson CM30 pulls 1.9 amps; with that said, is it necessary to have a relay installed?

Also, what I am confused about is whether or not the ECU keeps the pump running constantly, except during a cold start. I saw a post where someone mentioned that, except during cold starts, the ECU keeps the pump running constantly. If that is the case, why wire it to run when the accessory is switched on?

I'm installing a new pump tomorrow and am trying to figure out the best/easiest way to do it.

 

The only advantage I see with a switch is too keep it running even with the car off ( which is a pretty good reason in it's self for track use ).

 

That makes sense, I guess the only question I have now is, is a relay necessary considering that Johnson lists a current draw between 1.7-2.2 amps. I see some are in fact using a relay, but is it really necessary?

 

OP, so you happen to have links to these threads as I'm trying to do the same today and wanted to pickup the right relay and wire it correctly. Thanks

 

I wired in a 3amp fuse holder near the ecu, ran a positive wire neatly around the engine bay and grounded the pump.
I didn't use a relay as current draw isn't high enough imo.

 

I am thinking of doing the relay since I will be getting a beefier pump down the line.
So what happens to the original power supply to the pump (triggered by ECU). Do you cut and tape off that trigger and where? Thanks for the quick response too

 

having a relay is like having two circuits. one circuit is for the trigger side of the relay which really doesnt matter. but the other circuit can be ran with all 10-12 gauge wiring for the pump so it doesnt jeopardize the vehicles wiring in any way.

 

I'm not sure what kind of current a Meziere pump pulls, but if it's more than the CM-30 I may be inclined to install a relay.

From what I have read there's only so much that can be done in the way of cooling mods before having to upgrade the inter-cooler itself, as it is the limiting factor.

 

I do get the relay part but in essence isn't the relay supposed to be the new power supply for the pump and if so shouldn't the old supply(Triggered by ECU) in order to prevent a possible overload when the relay is active (Supplying power to the pump) and the ECU's trigger for the pump also becomes active or what am I missing/what am I assuming wrongly?
I assume we're talking of a basic automotive relay such as used for powering fog lamps. Also is there a suitable always on 12V source under hood(powered by the rear battery?)

Thanks

 

I found another thread here with pics of a wire on the drivers side/under hood that is switched on when the key is in the #1 position. I tied into it with a splice then wired a fuse holder in-line right after the splice to protect the wiring behind it.

 

I plan on the meziere as well in once I get some other stuff done but given all its great reviews and flow and what not I'd rather go the extra precautionary mile to have a relay. I want the pump switched as I found out yesterday at the truck that my system works great so long as I'm on boost so despite always seeing 15-18 above ambient during everyday driving, I never saw less than 40 above ambient and my heat exchanger was ice cold: translation, IC pump was not running but when I'd get on boost for just a second and back off, the IAT's would start to fall (pump on).

 

I have a CM-30, thus the reason I only used a fuse instead of a relay. A bigger pump would most probably pull more current, possibly requiring a relay.

 

Incorrect. All the pumps are run off 12v, so you just need the proper wire size and fuse. A relay could be used to send power to the circuit under certain conditions (e.g. like the factory setup).

The REAL question is when does the stock system send power to the pump ? I have read so many bogus / conflicting threads, it would be GREAT if someone had a definitive answer - ideally an engineer from AMG .