I have a 2.5L merc repair manual at home. I'll look up the wiring for you. I know that in some trouble shooting that I have done for my 2.4 you need to make sure the switch boxes are always grounded to the block during t/s. I have also had the same problem you are talking about happen to my efi 2.4l I found the ground wiring for the ecu broken off. Reconnected the ground and no more trouble. Later, Gary.