allright, im not very good with diagnosing electrical problems so maybe yall can help.

1st thing that started to go wrong:

when i depress the brake pedal, my drivers side turn signal would come on (constant,NOT blinking), both the actual light and the indicator light in the dash. when the driver side turn signal was engaged, and the brake was NOT depressed, the turn signal would function as normal. this problem has been going on intermittently for the last few months with no other problems.

2nd thing that has now gone wrong:

the first problem still exist but now my tail lights do not function whenever i turn on my headlights. the headlights still work, the brake lights still work when the brake is depressed and my turn signals still work in the same manner as described earlier. when i replaced the 25amp(?) fuse it blew instanly as i turn the headlights on.

now what do i do? lol...seriously, i have no idea where to go. ive looked for cuts in the tailight wire harness to see if it was grounding somewhere on the chassis. the bulbs "look" to be in okay shape. what else do i need to check before i decide to tape flashlights with red filters on the back of my bumper?

When did this start? Has any electrical work been done on the truck? Do you have a trailer light connector added to the truck?

Check the grounds, check the bulbs, check the connectors, check the wiring.

I once had a problem in another vehicle with a broken conductor inside a tail light socket. The broken wire was the ground conductor and the problem showed up at night when the brake light would not work, in fact the tail light would go off when the brakes were applied. In the day, things worked normally. Turns out the brake light was finding a ground path through the parking light, until the parking light was turned on, that is. Parking light would in turn find ground through the brake light, again until the brake light was turned on.

Is it only when you turn the headlights on, or when you turn the parking lights on? Seems the brake light and turn signal/parking light are crossing paths where they shouldn't. I had trouble with a broken contact down inside the socket where the bulb itself plugs in. I didn't experience the problems you are having (mine just didn't work), but you may want to look at them. I'd pull one bulb at a time, checking the lights each time, until the problem goes away. If it does, then you've found the offending bulb, socket, or circuit. If it doesn't, then it's in the wiring. I'd start with the combination bulb in the bottom of the taillight.

did some more checking this afternoon. looked at what i think is the "tail light relay?" the relay was hot to the touch and the truck had not be run all day. could this relay be the suspect? tried testing it like the FSM says too but my multi-meter seems to have taken a dump so i just ordered a new relay from napa just in case. well see what happens. thanks