It's a computer module integrated into the under-hood fuse box. Instead of a simple backup light switch that sends current to the backup lights, the switch grounds a 5.0 volt signal to tell the computer to turn on a switching transistor to send current to the lights. It also has a circuit to ground the coil of the starter relay when the neutral safety switch tells it to. On the full-size trucks it runs the three 4wd lights on the dash, the horn relay, and the power to the movable pedals, among many other things.
Ford calls theirs the "FEM", for Front Electronic Module. Chrysler's term is "Integrated Power Module".
Did you ever play the game "Mouse Trap" when you were a kid? You built a really complicated set of levers and triggers to catch a mouse. By the time the cage came down, the mouse was gone with his food morsels, got married, had a family, and came back for more food and got trapped! Well, that last part was a bit of sarcasm, but the point was they took a simple idea and turned it into a really messed up, complicated, unreliable invention. I think about that game every time I see another computer added to a car. Just because they CAN do it doesn't make it any better for the owner or the mechanic. These computers pretty much guarantee planned obsolescence. It's easy for aftermarket manufacturers to build a switch or any other replacement part you could want for a Model T, but how many companies will be repairing a computer for a car when it gets to be 40 or 50 years old?
Thursday, April 7th, 2011 AT 9:21 PM