ok i swapped it out with the ac fuse, the horn was a 15amp and theVECHMSL was a 10amp. and the ac still worked and the 3rd brake light didnt

also there is a BIG gray cube-lookin fuse labeled CHMSL at the bottom of the fuse box and then there is the TRHMSL and the VECHMSL at the top of the fues box. i checked the small one that said VECHMSLl but i didnt check the one that said CHMSL

 

The cube labelled CHMSL is the relay. Swap that with another in the box (horn possibly) and check the horn for proper operation.

 

ok i tried but i seem to have a problem. the diagram on the inside of the fuse box show where the fuses go but theHORN relay doesnt fit into the place for the CHMSL




the CHMSL in thediagramis just to the left of STOPLP 20A and TBC 10A

Below is a picture of my fuse box. the only thing i have taken out is the HORN relay. there was nothing where the CHMSL is supposed to be and the holes for the horn relay are a different shape than where the CHMSL relay should be



at the place where the chmsl should be, there are 6 holes instead of 4 like the horn relay. the rightmost 4 holes of the chmsl spot are the perfect size for two of the smaller 10A or 20A fuses. it seems almost like there was never a chmsl there in the first place


thanks for allyou're help so far

 

another thing you can try is after you take out any of the above fuses related to the third brake light take a test light and see if your getting power to the relay itself thats a quicker way to check it as well then there isn't a realy jumping contest going on cause if there is power to the relay and your light still doesn't work then just replace the relay thats all it sounds like really just a bad relay and is probably a couple bucks at the part store.

 

I fail to see how a test light would be faster than swapping the relays and hitting the horn... Not to mention that you never did state which cavity to probe for power... Also, most probes on many of the test lights that I have owned/used have been too big to probe the cavities in modern fuse boxes.

These third brake lights do fail every once in a while...

 

my fault i was thinking of something else swartlkk i didn't realize it till you said something your right with switching the relays around to get it to work or not

 

From his previous post, it sounds like he didn't have the CHMSL relay in his truck...

That'd make it not work...

But the relay should still swap between the horn and the CHMSL socket...

I'll go take a peak at my fuse box and see if she looks the same...

edit:

Well, according to my under hood fuse box, my CHMSL relay isn't under my hood...
It's the same shape and # of holes, but my relay isn't there... And doesn't show up on my fuse/relay diagram...

So it could be that your relay is under the passenger side of the dash...

However!

It's really easy to see if you're getting power to the light...

Open your back hatch, and take off the entire panel that your cargo area light is attatched to (it just pulls off, or should, anyway, it does on mine) and you'll see a square or rectangular hole in the roof (I forget which) and there'll be wires in it, with a plug... disconnect the plug and test for voltage, or use a test light...

A floor jack handle is perfect for wedging between the seat and the brake pedal...

 

yeah there was not a chmsl relay to begin with and the holes dont match up

 

Well, now you either get to go digging under the passenger side of the dash, or popping off your cargo light panel... Hopefully it's just as easy in a 4 door as it is in a 2 door...

 

That is quite odd... The 98 owners manual from MyGMLink.com showed the CHMSL relay to be in the corner of the underhood fuse box closest to the driver's side door.