Ok so I'm selling my truck, well trying to. I have a 91 f150 4x4 5 speed transmission. This truck has a lot of work into it, runs great. However, I can't get anyone to buy it because of the check engine light. The problem is, the computer was never switched out after it was converted. I think everyone is scared to buy it because of the check engine light. What should I do? Fork out the money for a new computer? Where would I find one? Will it remove the check engine codes for automatic transmission?

 

Any auto parts store can get you a new computer for your current application( you did say you converted to manual?)
Is the transfercase manual?
Also rockauto.com
Generally, the computer controlled auto transmissions, when missing, will set codes because the computer expects to 'see' the auto transmission there.
If it were me, I would hit up a picknpull and try to find an identical truck with a manual to take the computer from, before buying a new computer.
Either way, you'll get that money back when you sell it as a "no issue" truck. Check engine lights will always lower resale value

 

If getting a standard transmission computer from a pick n pull, will it work or does it need to be a specific computer? I can swap parts but I don't do electrical lol

 

Regardless of where you source the computer, you'll need to guarantee that it comes from/for a truck with the same year as yours, as well as the same motor. For instance, I have a 96 f150 with a 4.9l 5speed. If I changed to an automatic, I would need to ensure the computer I swap is for/from a 96 f150 4.9l e4od truck.

Swapping the computer is easy. Big old harness near the driver side fender well that you can unplug (after removing a bolt) and slide the computer right out.