Sunday, when it was 70* out, I went to test my ECU and my wiring (Ford EEC-V on a 5.0 in my 77' Cherk), which I spent 15+ hours doing. I though I would be smart and use a battery charger for power since: 1. I don't have battery cables yet. 2. The charger is limited to 15A. 3. It has these neat clippy things and an easy to use and get to power switch, should things go awry.
So I hook the positive lead to the power distribution center stolen from a GC and the negative lead to a ground stud and flip on the switch. Ammeter doesn't move, so no shorts so far. Turn the ignition on, ECU doesn't turn on the fuel pump and there is a loud buzzing from the engine. Turns out to be the IAC. Plug the scanner into the DLC and it can't talk to the ECU. My dad and I spend almost two hours chasing wires and find nothing wrong. We give up and I start searching about OBD-II DLC's.
Next day after more info, I find that pins 4 and 5 on the DLC need to be grounded and pin 16 needs constant 12V. Quick wire job later, including a temporary MIL, I try again using a real battery hooked up using 16 AWG wires, just in case. Everything works fine. IAC doesn't buzz and I can read all sensors with the scanner and the ECU drives the fuel pump like it should.
So, a battery charger won't run an ECU. Not my charger anyway. Oh, and it is now 20* outside with 8 inches of snow.