Attention: TDR Forum Junkies 
What the... ? Stands for "Center High Mounted Stop Light"
The same circuit that powers the CHMSL also triggers the brakes on your trailer brake harness. No CHMSL; No trailer brakes. And... possibly even worse (?)... I discovered my regular brakes would come on a couple seconds AFTER the brake pedal was depressed when I had no CHMSL fuse.
Another symptom of no CHMSL fuse is no brake lights w/o ignition switch. So apparently there's some kind of 'power assist' thing going on; which explains the delay when under power but still works (slow; slow enough to get seriously rear-ended if hard braking).
Apparently the dealer removed my CHMSL fuse when they fried some of my other fuses when it was in the shop; and missed replacing that one. Of-course; the only reason I know for a fact they fried some of my fuses is when I went to pick the truck up there was no instrumentation. I immediately went back into the garage at the dealer; and we discovered a-lot of loose fuses in addition the cooked instrumentation fuse. That was about 5 weeks ago! Thank god I haven't been rear-ended since then!
Went to get my trailer brake controller hooked up today and they advised me to go to the dealer and find out what happened to the third brake light wiring since the controller wouldn't work without it. The dealer was clueless; of-course; appt. made for Monday. Went home and figured it out in 10 minutes. At that time had no clue what "CHMSL" meant but figured if it didn't say "spare" then there should be a fuse in it; problem solved.
So... Beware the CHMSL. If you're towing and your 3rd brake light stops working... . make sure the fuse is good or it ain't just the brake light! You don't have trailer brakes either!
The same circuit that powers the CHMSL also triggers the brakes on your trailer brake harness. No CHMSL; No trailer brakes. And... possibly even worse (?)... I discovered my regular brakes would come on a couple seconds AFTER the brake pedal was depressed when I had no CHMSL fuse.
Another symptom of no CHMSL fuse is no brake lights w/o ignition switch. So apparently there's some kind of 'power assist' thing going on; which explains the delay when under power but still works (slow; slow enough to get seriously rear-ended if hard braking).
Apparently the dealer removed my CHMSL fuse when they fried some of my other fuses when it was in the shop; and missed replacing that one. Of-course; the only reason I know for a fact they fried some of my fuses is when I went to pick the truck up there was no instrumentation. I immediately went back into the garage at the dealer; and we discovered a-lot of loose fuses in addition the cooked instrumentation fuse. That was about 5 weeks ago! Thank god I haven't been rear-ended since then!
Went to get my trailer brake controller hooked up today and they advised me to go to the dealer and find out what happened to the third brake light wiring since the controller wouldn't work without it. The dealer was clueless; of-course; appt. made for Monday. Went home and figured it out in 10 minutes. At that time had no clue what "CHMSL" meant but figured if it didn't say "spare" then there should be a fuse in it; problem solved.
So... Beware the CHMSL. If you're towing and your 3rd brake light stops working... . make sure the fuse is good or it ain't just the brake light! You don't have trailer brakes either!
