Fuse keeps blowing when I turn on the headlights.. they work but dash lights n t on 1994 GMC 1500 Pickup

Everytime i turn lights on it pops n blows fuse again replaced switch n checked for bald wires n bulbs

Asked by for the 1994 GMC 1500 Pickup
Lot's of possibilities, these are a few i have found: Any add on accessories ie, new radio with illumination wire hooked up to the wrong terminal? Wired up for trailer towing and wires are shorted there? Any rear bumper damage lately that may have shorted tag lights?
I did recently add a towing wire kit but it has been at least 2 was since I have n no problems till now
Unplug harness, under rear of truck near bumper drivers side,that is going to the trailer wiring and rear lights and try it to see if short is now gone. If do check from that point back to rear light assemblies. Possible bulb circuit board problem in tail lights.
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2 more answers , 3 more comments
Check your tail light bulb circuit boards, They give a lot of problems, with twist in bulbs (1157-1156) they burn out and short. Just a thought.
Check to see if the roller switch that controls the brightness of the dash lights is separate from the switch you replaced. This component could be shorted. remove it and inspect the connector. sometimes a loose wire can arc and if it has for a while, odds are good something will be black or burnt. Otherwise you may be in for a bit of looking...
I even left that roller unplugged to see n it still blowed.. there is time it will work for a little bit but them blow . It seems to when deciding to work it does until I put it in gear.
You said it only happens when you put the trans in gear. Does in happen in drive and reverse? Are you sure it's not when you depress the brake pedal? (to take it out of park)
I have checked the brake even replaced to switch.. I have replaced the the bulbs board on rear drivers side n also completely unplugged trailer harness.. the courtesy fuse sparks when putting it in but that is not the one that blows. it is the one below it that is connected. It blows Everytime u turn on park lights...