Possible PCM issues
 

so i just bought a 1999 ford f150 extended cab, 2wd pickup. its auto with a 4.6 . and i got it for 600 bucks, cause the people that had it got tired of fooling with it.. here is the current issues it has, guy that had it put a motor out of a 1997 in it, had cranking issues for some reason, switched pcm on it, now the tach/speedo is a no go, no interior lights, theft light rapidly flashing , truck still cranks like that but its going nuts. what would be the problem? i also think the alt is dead, pulled pos cable off while it was running and it killed instantly. it was just a quick run over of things, but the pcm is where i am worried. i have two more pcms that came with the truck but i have no clue what one goes to the vehicle. to add to the changes to the truck, the odometer also reads just dashes , no numbers, the oil pressure/coolant temp /mil light is on constant, but good oil pressure, and coolant temp

I would really try the other computer ...but ideally find the computer that came out of the donor vehicle. At least then you have a starting point. GEM not compatible or wrong for the PCM that is in it??? Good Luck...sounds messy.

The Dash/PATS and the PCM have to match otherwise no start unless a dealer reflash is done.
The key has to match for Pats, also.
This is why the Theft lamp is flashing.
Once you get this in place, there may be other issues.
Bottom line is you have more than one problem to deal with at the same time causing all the confusion.
When getting someone elses mess, you have to do a lot of learning to be able to sort out all the issues you don't know about otherwise the vehichle becomes useless for more than just parts as the previous owner found out.
First order is to get the matching PCM to the truck, in place.
Then the original keys to the truck.
Get the theft lamp issue solved, then go into motor trouble shooting.
You may not have even gotten a deal for $600 if you can't get it into running condtion.
Good luck with it, let us know how it goes.

got it running good, no more theft light issues, i found the original pcm with the right calibration code , now tmrw i gotta do my electrical diagnostics for the ac , blower fan, drivers side window, and the reverse/cargo/interior lights . the bulb isnt coming on when i open the door, ill get my wiring diagrams and check it out.

There ya go.
You just now got a deal at the expense of the last owner not knowing what's was going on.
Knowledge is power!
You spare PCMs are useless to you unless programmed.
Good luck.

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here it is, my 600 dollar beauty. 202k miles, 4.6 v8, auto, supercab 4dr, i changed the carpet out for the more robust rubber floor i got from the junkyard for 40 bucks

only problem now is i cant seem to find the right wiring diagram for the alternator , used a good junkyard alternator, no charge, also driver side window is inop, relay is clicking, just no moving, and the climate control isn't working. tried all settings , and the fan switch, no bueno on that. oh and the trash in the yard. i have a year old lab that goes and get's other peoples junk and brings it home.

LOL...he has a nice selection going. Dogs....gotta' love em'

That's a nice looking truck. Glad you got it running. Pick away at the rest now.

Nice truck. My 1999 heater controls didn't work, I pulled them out and sprayed contact cleaner on the posts and they work now, but the vacuum operated switch isn't getting any vacuum to it. I will fix that in the spring, it goes to full heat, defrost default position now, good enough!

whatever this guy did to the truck, he really f ed it up. i have been tracing wires for the past few days and im probably overlooking it but. right now i have no power windows, driver side window inop, switch is probably bad, its acting up anyway, alternator not charging, its good , did on and off vehicle testing. no blower motor activity at all , no interior lights, no reverse lights, the plug to the voltage regulator was a bit loose and jiggly so im gonna replace that, and i found a ground strap from the body to the engine missing. so there might be some of my issues also. i forgot to mention i have no power mirrors either, fuses are good for everything, i just am sorta lost in the sauce right now.

when i got the truck i noticed a hackjob he did installing a radio, hopefully he didnt short out the whole wiring harness in the truck