Here's that deal:
A "5 pin" ECU REQUIRES a 4 terminal ballast
A "4 pin" ECU CAN use EITHER 2 or 4 pin, but only needs a 2 pin ballast
You can NOT tell (all) 4 terminal ECU's from 5 terminal because at least some 4 pin ECU's HAVE 5 pins, it's just that one is not hooked up (a dummy). You must use an ohmeter to find out if the 5th pin is hooked to anything.
I have I think 3 or 4 "4 terminal" ECUs and every one of 'em have 5 pins.