1994 Chevy C1500 Truck Brake Light Mystery

does the relay look like this? and what were the final results you found with your meter?

I did disconnect the brake switch at the pedal. It made no difference.

No person, at Chevy parts counter, or at service dept, nor at two aftermarket autoparts stores, was able to tell me what this relay is dedicated to.

I pulled fuses one at a time while the tail lights were stuck on.   All the likely candidates did nothing.  So I went at them one at a time.   I got to the CTSY light and bingo.   I'll assume that CTSY means courtesy, or dome,  light.     Now the dome light never did work on this truck.  In fact, ironically, it was the only light that would not work when I bought it.    I stopped at autovalue on the way home from buying the truck and got a bulb, but to no avial.    But ALL the other lights worked properly.  

Today, when I discovered that the CTSY fuse opened the troubled circuit, I began to really wonder.  The door switch for this light is missing on the driver's side.   There are a couple of small plugs near this point (in the vicinity of the parking brake) that are dangling unconnected to anything.    I'm next going to get a switch to replace the missing one and connect it, although logically I cannot imagine why a missing switch should gum up the works.    A switch is open normally.  If it's missing/disconnected the system just thinks it's open... no?   Why the heck to engineers do this crap?    Someone told me that on some of these Chevys there is a separate fuse for 'courtesy' and for 'dome'.    If one or the other is circuit is not complete, it keeps the other one from working.   

I have a Puch moped at home.    I was online getting info on it one evening and someone on a forum was having a hard time starting the bike.    Another member told her to make sure the bulb was good in the taillight.  They explained that on some s the ignition would not function without a complete circuit through the taillight.   No,  this is not a safety feature.   It's a PITA gremlin that the engineers just let pass.   And this from a MOPED!     This isn't computer or microcomputer stuff folks.  Why does it have to have been made so complicated?   

The guy at Autovalue tonight, after poking around with a meter for 15 minutes (extremely kind of him) advised me that if all else fails, I ought to work around this relay entirely and hard wire the brake lights myself.   I'm afraid that this is just asking for more trouble.   I'd next find my headlights screwing up, and my turn signals, etc.    

Can't I just enjoy a basic chevy with manual transmission and roll up windows?    I was so happy last week. 

ckeeler, that's not the relay.    Mine has four spades in  square arrangement.\

I'll post a pic if neccessary.