I just picked up a 99 F150 for a song because it has an issue with the PATS system and the po doesn't have a clue on what to do with it. I bought a new ignition cylinder and Auto Enginuity to program the PATS. The problem I'm having is that I'm not getting anything from the OBD2 port and the #3 fuse is good. What else would cause the port not to have signal?

 

You have to make sure PCM gets power too. Check all fuses and relays pertaining to PCM.... then to program RAP or PATS, you need to verify that no component in RAP is bad. Just because you bought a new ignition cylinder doesn't mean you'll be able to connect to the alarm module. In fact there are various components in PATS system. I never knew anyone to get around it, outside of dealer. This includes professional locksmiths using programming equipment.
Good luck

 

Add some more info.
Does the motor start?
Did you access the dash diagnostics?
Do you have the original programmed key?
Is there a CEL light on?
Has the dash been changed?
Establish a baseline before making any changes.
Are you sure nothing has been done before you got the truck otherwise it will be a long discovery process finding out or your no better off than the last owner...
Ignition switch only applies power to the dash, for cranking, to operate the PCM relay, not the PATS system.
Recognize all the separate issues first or confusion will reign.
This is the 'joy' of buying some one else's problems.
Good luck.

 

The back story is original owner was using the truck as a daily driver, then one morning the truck would start, then stall almost immediately and the anti theft light was on. He was moving out of state and didn't want to deal with it so he sold it dirt cheap to a friend. The friend (who I bought it from) replaced the receiver halo and ignition cylinder out of a savage yard but didn't know it needed to be programmed and didn't want to deal with it anymore.

I bought the truck for what owner 2 had into it. I bought an ignition cylinder not knowing he had 2 keys before I picked it up, dropped a freshly charged battery in. It cranks only. I plugged in Auto Enginuity but it wasn't linking. I checked the #3 fuse and it didn't look blown but the link looked funny so I replaced it. AE still wont link. I do have the original key, cylinder and halo.

My first step is to be able to get the OBD port working so I can go from there. All other fuses are good, next I'm going to check the relays. I don't know if any of them control the PCM haven't made it that far, I've only messed with the truck for a couple of hours. My main question is what would cause the OBD2 port not to work besides the fuse?

My plan is to get this thing running and drive it while I do some work on my truck then sell it and make a few bucks. If this turns into a worst case scenario I can sell it for scrap and still make a small profit but would likely part out what I can.

 

Use a voltmeter and measure for 12 volts on pin 15 of the DLC.
Bottom row last pin on the right.
Make sure the pin is not bent over or pushed back.
Be sure you Scanner is good.
Good luck.