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Fuse/relays with PDM

EFI Wiring Fundamentals

Discussion and questions related to the course EFI Wiring Fundamentals


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I'm building a harness with a Haltech Elite 2500 and Smartwire PDM.

Is it not OK to have the PDM supply power to everything in the vehicle?

Can the PDM supply the 12V to ignition coils, injectors, ECU, or do these need to be direct to the battery, with fuses?

Thanks! love this site.

If I have enough circuits available the only things that aren't run/supplied by the PDM is the alternator output and suppy to the starter motor.

Hi David,

I have seen before in the manuals for the ECU and a PWM fuel controller I am using, to connect main power directly to Battery +.

I am concerned with this note from the Smartwire manual.

"Note: Most ignition and ECU systems require a direct main power connection. This main power connection must go directly to the battery. DO NOT connect the main power wire from these devices to the SmartWire outputs. Each of these devices will also have a small wire requiring an ignition switched power source. This small wire will connect to an output from the SmartWire."

I don't follow the motivation for this note? The outputs are 10-20A and can be doubled up if more current is needed.

So long as the output to these devices is constantly on, what is the risk? I would like to power everything through the PDM, but want to make sure it's safe to do so.

I'm not certain why RacePack would suggest that you 'must' wire directly to the battery. I don't.

Fair enough. I spoke with Racepak, and they didn't seem concerned with powering these devices through the PDM, provided you are able to supply sufficient current.