So I had a bad front control module. It was causing me to have no blinkers, wipers, brake lights, and my headlights stayed on 24. I installed a new FCM today and now everything works except for my headlights. If I plug my old FCM back in the headlights come right back on. Does anyone have any ideas what could be going on?

 

New or used FCM?

 

Used FCM. I bought one on eBay and got one from a junkyard. Both of them do the same thing, everything works but the low beams.

 

Then there is something else going on.

 

I noticed that it’s not my headlights coming on with the old FCM. It’s the brights, so no headlights with the new FCM or the old one. Could it be the switch?

 

Holy smokes, what an overly complicated system..... That's insane. Why they think they needed that level of complexity is beyond me.....

But, here goes....

The headlight switch merely modifies a signal it gets from the insturment cluster, to tell it you want the headlamps on..... then, the multifunction switch (dimmer switch) gets yet another signal from the cluster, and the switch modifies THAT to tell the FCM whether you want high or low beams..... That switch uses the violet/orange, violet/tan wires to 'suggest' to the fcm what to do. Question becomes, is it getting that signal? Do your beams not switch? Or do the highs go off, but the lows never come on?

I think at that point, the cluster tells the FCM via the PCI bus, what to do......

 

With the new FCM I can turn the highs on and off but the lows never come on. With the old FCM the highs will stay on at all times if the truck is on.

 

Hhhmmmm..... so apparently, everything else is working right..... more or less.... Might try another used FCM, (as I can't find an internal wiring diagram for that....) see what kind of behavior you get. It's possible that you got one that was broke in a slightly different way.... if it still doesn't wanna work. I just don't know.