I purchased a 2003 7.3 last month and the door ajar light was illuminated on the dash. Didn't think much about it...figured it was a sticking door sensor switch. I did the wd-40 trick in all of the latches. No luck. Tried the process again. Still no luck. I finally break down and take it to a dealer and pay them $80 to do an electrical diagnosis. They kept the truck nearly 4 days. Long story short - they said that it looked like somebody (a previous owner or mechanic) had replaced the Vehicle Security Module with an improper VSM. My truck is a 4x4 crew cab Lariat...they said maybe that VSM came from a 2-door XLT. They said several wires leading to it had been cut and the others were spliced into it. They said their computer was reading all sorts of codes. They said that VSM was only showing the truck had two doors. They said it would be significantly more money to further diagnose this problem and they said if the dome lights are the only thing that doesn't work, then just live with it.
I could live with it, but it sucks to not have dome lights when we are trying to load up three car seats in the back seat in the dark and I hate seeing the red idiot light on the dash all the time. I also cannot get the truck to enter program mode for the keyless entry remotes. They said these problems both run through the VSM. I am so disgusted with these issues that I am contemplating getting rid of the truck on getting something else.
Has anybody had experience replacing the VSM? Where is it located? How easy is it to access? How much does a new VSM cost and can I install myself? They said they had the whole dash removed and of course I couldn't go back in the Ford shop to see what was happening due to insurance and shop policy. Any help or thoughts would be appreciated. Thanks