I need to build a bench harness for my e38 ECM. There's oodles of computer power supplies sitting around, and those have a 12v output on certain wires. Would you use one of those, or would I be a lot better off using a 12v lantern or car battery?

Personally, I'd rather use the computer power supply, just for simplicity and low cost. But if there's any problem with electrical noise and inconsistency, I'd like to know that before I regret it.

 

Any 12v source that can put out about 1 amp will be fine. Beware some wall warts say 12v but put out much more and there is very little Ac ripple filtering on them.

 

I would use a battery long before I would use a switching supply like in a computer. Just put a battery tender on it, you could even use a garden tractor or motorcycle battery. Personally I use a wall wart most of the time because of its portability but it is a quality one, that I did put an O-scope on and looked at the output and ripple

 

I have 10+ bench harness and have flashed thousands of ecm's over the years, I started out with a power wheels 12v charger for years, used a 12v battery and been using a 12v 5amp power supply now for the last 10 years with zero failures.