On my 90 f-150 2wd 5.0.

1. When i connect the neg cable(key not even in the truck) the fuel pump kicks on for a couple of seconds. I'm pretty sure that this is my battery drain problem, but i'm not sure where to start looking. I swapped out the PCM from my parts truck and still the same problem.

2. The horn only works when the key is in the off position. I swapped out the horn button just to see and no change.

3. When i tried to run a code test the light wouldn't even come on to show codes or system pass. Sometimes when i turn the key on to start it the light will come on for a few seconds like normal other times it doesn't at all.

4. I think im down to the last option but wanted to ask. Sometimes when i start it or at random down the road, the rpms jump up to 3k and stay unless i put it in gear then it idles down but still high, and will idle high while driving. I replaced the IAC(twice) cleaned the throttle body, made sure the valves weren't sticking. but when i unplug the IAC it will idle almost normally little bit too low. Am I safe to assume that the TPS has gone bad? or is there something else that it could be.

I was hoping that the PCM was going to be the fix for my other problems as well but it seems not.

 

The first 3 problems together, make me think the problem could be in the key cylinder/column/ignition switch. Like the truck thinks the key is in a different position than it actually is. Sounds like the pump is priming soon as power is applied.

 

^^ agreed. Sounds like the issue(s) may be ignition switch related. Perhaps take a look at your switch to check for cracked or broken ignition housing, corrosion etc.

 

A coworker and former mechanic told me that the windshield/cowl can leak on top of the fusebox and cause shorts. If your ignition column switch is working as intended, i'd check your fusebox for signs of corrosion. Good luck!