I just completed a full wiring harness swap in my evo 6, and I'm now having issues with low voltage at the ECU. I'm unsure if this was an issue before the swap as I purchased the car not running with a butchered harness.

With a battery with a charger on it holding a good 14v, I turn the key on, the cluster lights up nice and bright, but the ecu does not have enough power to boot, and will not connect to my laptop via USB (it is a link g4+ pnp). I measured power between pins 12 and 13, which are supposed to be unregulated power from battery and chassis ground respectively, and it has about 6v there.

I also removed the ECU from the car and tested it on the bench with power direct to pins 12/13 from the same battery, and the ECU booted fine and connected to the PC Link software.

Has anybody seen this before? Any suggestions about where to look for issues?

 

Found my issue, there was a pin on one of the main harness combination plugs that got pushed out, that pin happened to be the main power supply for the ECU relay