Well, that about says it all. Fed it 3 of the 25A "Flasher" fuses. Turn signals nor any brake lights work. This is REAL bad timing.
:help2:
Any suggestions?

I might add it's a 2003 4WD crew cab.

Alright, I'll throw this one just for the heck of it.. I had a similar problem in an old Chevy Citation I inherited from a relative. Brake light/turn signal fuse would always blow.

When it came time to sell the vehicle, I pulled the aftermarket radio out. Whoever put that radio in, ran a ground wire to the chassis of the radio. Once I removed that wire, the fuse stopped popping. Mind you, the radio's fuse never once popped. Drove the vehicle for another two months and never replaced another fuse.

Now I'm fairly bright when it comes to electronics, but never did figure what relationship the chassis of the radio had with the taillight/turnsignal circuit!

Any chance any new electronics have been installed recently?

Nothing new added to truck since I bought it used 2 years ago (not even a tuner)!

If it blows as you install the fuse, IIRC the flasher isn't shorted. Otherwise, there is module for the lamps. Read #8 http://www.dieselplace.com/forum/showthread.php?t=129585

Also, look for damage at the trailer plug wiring.

The 25A brake fuse under the hood blows when you hit the brakes. The 25A signal fuse blows when you turn the signals on. (I'm ashamed to admit that right now I have a 30A fuse in the signal and it'll live for 4-5 blinks at least). Lord, I apologize what me with the starving pigmies....

Any other suggestions?

I'm suspect of the headache rack (not new). As there's a lot of wires that the customizer in TX ran right through the floor pan with no grommet or anything. Some go to the extra fuel tank valve, and I'm not sure where some go, but imagine some go to the stop/turn lights in the headache rack and somewhere else...

Check your trailer plug in the rear for corrosion, seen alot of problems with them after the truck has seen several winters or seasons of boat launches.

Dealer advised that brake/signal module was bad and replaced. $229 dollars later, both fuses blow before I get out of sight of the dealer. Any ideas?

...
I'm suspect of the headache rack (not new). As there's a lot of wires that the customizer in TX ran right through the floor pan with no grommet or anything. Some go to the extra fuel tank valve, and I'm not sure where some go, but imagine some go to the stop/turn lights in the headache rack and somewhere else...

I'd start right there and see if you can find a short.

Dealer's had it 3 days. Says they installed HD flasher, replaced module (again), found 8" of bare wire out back and a bunch of melted together wires at trailer junction box in back. They now have brake lights working, but not T/S.

I advised them that before I brought it in, a 30A fuse allowed T/S to live, but every time they flashed, dashlights would dim, so there's a short happening somewhere.

There's no telling right now 1) what this will cost and 2) if anybody can fix it, as they're running out of things to check.

I just love trouble shooting by smoke. Bigger fuses can actually start a small fire where the problem is to make things a lot easier to find. Do it all the time in electronic repair!

Well, they finally found the problem on second checking of wire running up thru bed corner to headache rack. It was the first think I told them to check. Not sure if this is even related to the melted wires at the back trailer junction box (one socket in bed and one at bumper). I know the one at the bumper isn't wired right for my trailer, as the electric brake controller is useless, trailer turn signals didn't work and clearance lights/tailights didn't work (only think working on trailer from that plug is brakes). Could that have melted wiring? Trailer worked great with my '97 3500 (6.5L).