DRL & CHMSL are dead

Ok guys I have a tough one that has had me stumped for 3 days. I purchased a used 99 Silverado last month. Truck is in really great shape but has 2 things bothering me. The Center High Mounted Stop Lamp doesn’t work and the Day Time running Lights do not work right. On the CHMSL I have checked the bulbs their ok, even replaced them in desperation. Followed the wiring backwards to the center panel, next to the brake. Wires good has continuity. Now I’m not sure how to problem solve this connection there are several wires in this plug that I assume go to map lights dome lights and high brake light as well but when I checked a couple of the connectors they had power. Now I followed it on a wiring schematic to the Under hood Electrical Center to the CHMSL fuse and it is good and the socket has power going to it. Even checked the brake fuse on the side of the dash. Heard that the turn signal relay and fuses may affect this, so I checked them as well and they are fine. My brake lights in back work fine which has me wondering about the stop lamp switch, which I checked anyway the orange wire and the white wire have power but there are 4 other wires on the switch and I’m not sure what combination works the rear light, CHMSL and the cruise.

Now the DRL doesn’t work as well. The regular low beam headlights are on, turn signal and side markers but the lights next to the turn signals are dead. I have replace these bulbs as well checked the DRL relay, checked it partially pulled out for power it does have power, checked the DRL fuse it is fine and the socket has power. Does anyone think this is just a fluke that 2 problems exist or do you think they could all reside in 1 relay or connection? I have already changed and rearranged fuses relays and jumpered connections and still can’t figure this one out. Any thoughts will be greatly appreciated.

sounds like u need to check the grounds for the curcuits at the bulbs for drl and the3rd brake light.

I think I will start looking at ground connections but I need to find a better wiring diagram than the Haynes manual. It is not very specific but useful for basic wiring diagrams. There could be numerous grounds for those two lights and I can only think of two right off the top of my head. Does anyone know where you can find a good wiring schematic for this truck. I thought about a GM service manual but don't want to waste 70.00 to 100.00 dollars if it doesn't help.

My CHMSL was out when I bought my 99 Z71, but all I did is replace the bulbs. I also noticed that the little black pieces that hold the bulb, the contacts inside the socked would become bent and not make good contacy with the bulb.

Here is something else I didn't think about. When I bought the truck the fellow had removed the fuse to the ABS pump because it was running all the time. Im having Gavin fix that for me now but correct me if wrong but even if you remove the fuse to the ABS pump you still get the ABS light and Ebrake light on the dash. I have neither even when you plug the EBCM back up and put the fuse in.
I read somewhere that this model has a DSL module under the dash and if you unplug the C2 connector you will infact disable your DRL lights but your ABS and Ebrake light will go out as well.

I will check this tonight and let you know what I find.

hi got a printout of the drl curcuit .check grounds to bulbs . check drl fuse and drl relay under the hood in the elect. center . u can check the relay by swapping it with the foglamp relay or if u dont have foglamps swap it with another relay that has the same #s printed on top. make shure u have it in drive with the parking brake set so u dont roll away. if that didnt work try grounding the 86 pin of the relay by putting a small wire in side of the female hole the relay pushes into . if the lights come on u have a problem with the wire going to the bcm pos. a11 on the c1 plug lt green wth blk stripe. u could ground the wire at the bcm to check to see if your wire is good . if the wire is good , the bcm is bad ,or the ambient light sensor is bad or has a short. u could check the wires going from the bcm ,pos.a3 wht and a4 grey on plug c3 up to the light sensor on the top of the dash pos a grey pos b wht . hope this makes sense and helps. ps use a bulb test light instead of just using a wire straight to grnd. in case u get the wrong pos. by accident.a test light shoud be sufficent to trigger a relay depending on the resistance of the bulb in it.

Did you ever figure this out? I have the same problem in my 2003

I'd check for power at your CHMSL connector, the gasket leaked on my truck and only the brake light work(the bed light doesn't). Does your DRL system have a diode, they have been known to burn out and leave you without DRL