Hello
I have a 1997 F150 XL club cab 2 wheel drive that I can't seem to find out why the dome light doesn't work when either door is opened. The door ajar light comes on when either door is opened but no dome light. The dome light does work with the switch on the dash. Both door switches have been checked with a ohm meter and they are working fine. I have checked all fuses and removed both the battery saving relay and the lamp relay and tested them with a 12 volt power supply and Ohm meter they both tested good. I noticed the battery saving relay was in a closed position when I removed it which I think is normal. A friend said that it might be the Generic Electronic Module but he also said he thought a CTM was used on 1997 2 wheel drive. I have a ford cd service manual on this truck and it stated the GEM/CTM was behind the inside fuse panel but I couldn't find it. The diagram shows that pin number 22 on the GEM/CTM controls the dome light. All this module does is take the the power to ground and close the light relay. When I find the GEM/CTM I want to take the pin 22 to ground and see if the light comes on or measure pin 22 to ground with a OHm meter and see if the GEM/CTM is doing its job. This will at least tell me the GEM/Ctm is doing it's job and or I have a wiring problem.Has anyone ran into this problem and where do I go from here.
Ralph

 

Hi Ralph and welcome to FTE

Seeing that your truck is a 2wd XL it should use a CTM instead of a GEM. They are very similar though.
The CTM is attached to the back of the fuse box. You have to remove the fusebox to remove the CTM. It does sound like you've got the basics covered.

 

You want to measure voltage on pin 22, not ohms. The CTM has
an open collector transistor for grounding one side of the relay
coil. With the transistor "on", there will still be 100mV-200mV on
pin 22 which will throw your ohm meter reading off.