Ok so here's where I'm at. When I turn the key on the CEL flashes rapidly and does not stop. I tried another ECM and get the same problem. I also tried swapping PROM chips between the two, no change. The truck will start and idle, but its like in limp mode. It does not have any power, cuts out and sputters when you try give it some gas. The CEL turns off after the truck starts.

Here's what I all checked.

Traced all grounds, split off to engine/battery, no nicks and terminals are good clean connections.

I probed every pin of both connecters with key on and checked against the reference voltage indicated in a build thread wiring diagram. The only one that is even slightly off is coolant temp, at 3.65 volts. All others are right on.

I checked the CEL, has consistent voltage on positive side with key on.

When double checking the pins, I noticed that my connector does not have C2 (EAC). I'm sure I didn't remove this and do not think the harness had this terminal when we pulled it. I'm not sure if this would cause a problem or not.

I'm completely stumped here and have no idea how to proceed. I'm about to scrap this DIY harness and just buy one from AFI, but with this much time in it I'd really like to figure it out.

Please help.

Thank you.