GMC Repair: electrical problem, pain in the arse, dash lights

Question
I rebuilt a motor in a 98 gmc k1500 and when I installed it, as soon as I connect the battery the head lights come on,the fuel pump runs,dash lights are on with key out of ignition. I already replaced the ignition switch which did not change anything. The truck had an aftermarket programmer installed but I did not receive it when I purchased the truck. I was told that when the battery was disconnected for so long the pcm might go into failsafe mode.  Could this be the reason that this is happening?

Answer
yes that is true. you should disconnect the negative terminal only for 30 minutes. this will reset the PCM. if that does not work...it would appear there is a fault in the harness and you will have to check it very carefully. or....whoever pulled the programmer left something unfinished.

years ago I had a Toyota truck that did the same thing, and I ignored it and is fried the harness. I am not saying this will happen, but do not wait to fix this. If it gets to be too much of a pain in the arse, I would go to a salvage, or if you have the bank, go to ebay for it.

I buy most of my parts there. You may try to go to Pull A Part.