97 k1500 extended cab CHMSL and brake lights intermittent

I pulled the stoplamp switch out today. The channel that rides on the brake pushrod is broken off. Could be what reason they were working intermittently. Installing the new one after dinner.

No dice on the 3rd brake light. However, it did fix the intermittent rear brake light problem.

Based on the manual I think I have it narrowed down to:

A: A bad split that comes off C104-E
C104-E comes from the stoplamp switch. C104-E splits; one split runs to the stoplamp relay which works, the other leads to C298-F. (8A-110-0/1)
This is in the engine bay: 8A-201-24 Figure 38

B: Something wrong with C298 or wiring
C298-F is labeled TCC/Stoplamp switch output. Which I interpret as input to C298. However, the manual doesn't show where the output from the connector is (8A-202-8). So I am unsure how to test this one.

C: An issue with wiring on C411
C411-D is shown to feed power to the 4 pin connector on the CHMSL/Cargo light assembly that powers the CHMSL lights. However, there is no explanation of the pins in the manual (8A-202-44). Also, the manual directs you to 8A-201-40 figure 65 for the location of C411, but this is incorrect. 8A-201-40 has figures 67-68, neither of which has C411. Figure 65 is on page 8A-201-39, but it also doesn't have C411. The closest I can find is C410 for the rear speakers in the left rear of the cab.
Am I reading the manual wrong?

'98 manual has a diagram with C411 in it. Anybody know how to access that area? I haven't taken out any of the interior panels yet. Any tricks to it?

Found C411. No power on D with brake pressed. C had power which goes to the dome lights. C also comes from C298 so at least I know some things going through there are working.

C298-F is my next look, but the rat's nest under my dash isn't inviting.

Also, for anybody reading in the future, the easiest way to find C411 in a '97 extended cab, is to remove the ashtray and handle on the driver side back seat. Below there is a bucket that pulls out and you have access to C411. No need to remove some of the trim like I did (breaking some clips in the process).

Found something odd. While C104 doesn't have a detailed description of the wires through it in the manual, I think I figured out what is intended.

C104-A: Brown wire that goes from the parking lamps fuse to the rear parking and license plate lights (8A-110-5).
C104-B: I cannot find this on the diagrams. On the truck I found a purple wire in this slot next to the other correctly colored wires.
C104-C: Yellow wire that goes to the LH tail/stop-turn lamp (8A-110-0/1)
C104-D: Dark Green wire that goes to the RH tail/stop-turn lamp (8A-110-0/1)
C104-E: White wire that goes to C298-F that goes to the rest of the CHMSL circuit (8A-110-0/1).

I also think I found the connector on the truck, but it is directly below the brake booster, manual says master cylinder but this is more exact. None of the wires that run to the back of the truck after exiting C104 ever go back into the cab to find C298. This seems odd. Unless I have misinterpreted the diagrams, something should go back into the cab for C298-F -> C411-D.

I haven't yet found C298 in the truck. There seem to be a few yellow connectors that I do not think are factory, along with some module that has Ethernet cables running into and out of it. I think this is a trailer brakes module.

The yellow connectors are for the airbag circuits, they're yellow specifically for that reason - don't mess with them lol.
Now, my diagrams don't indicate individual connectors, but from my memory of the wiring on my 97, the white wire leaves out of the brake switch, goes through a connector at the top of the steering column support, then splice packs into several white wires - one of which went to the CHMSL without ever going through the firewall, though I don't remember every connector it passed through to get there.

Trailer brake controllers don't use Ethernet cables... I would sooner guess an add-on alarm module.

Have you checked in the space between the parking brake and the door? There are several connectors back there, most of them being for the door but there may be one going to the rear. You'll need to remove the kick panel on that wall.

Purple wire in C104 is for the fuel sender per FSM 8A-81-0.

Poring over the component locators in the FSM, I think I remember where C298 is now --- It's above the steering column support. You can't really get to it without tilting the dash down.

AK49BWL said:

The yellow connectors are for the airbag circuits, they're yellow specifically for that reason - don't mess with them lol.
Now, my diagrams don't indicate individual connectors, but from my memory of the wiring on my 97, the white wire leaves out of the brake switch, goes through a connector at the top of the steering column support, then splice packs into several white wires - one of which went to the CHMSL without ever going through the firewall, though I don't remember every connector it passed through to get there.

Trailer brake controllers don't use Ethernet cables... I would sooner guess an add-on alarm module.

Have you checked in the space between the parking brake and the door? There are several connectors back there, most of them being for the door but there may be one going to the rear. You'll need to remove the kick panel on that wall.

Purple wire in C104 is for the fuel sender per FSM 8A-81-0.

Poring over the component locators in the FSM, I think I remember where C298 is now --- It's above the steering column support. You can't really get to it without tilting the dash down.

Click to expand...

Appreciate the insight. I will see if I can get to it. The FSM isn't all that clear.

Did I misread it though? FSM definitely looks like it goes C104 to C298.

It does appear that way, like there's two lines that go to C104, but I know for sure it doesn't in fact, now I'd really like to know where the heck that white wire gets "taped back" after C104, knowing that would have saved me running a new wire all the way from my brake switch to my camper shell CHMSL ... I'm gonna have to look at my truck cuz my wiring from that connector to the rear is still factory for now, I would swear there was no white wire at all in that harness.

AK49BWL said:

It does appear that way, like there's two lines that go to C104, but I know for sure it doesn't in fact, now I'd really like to know where the heck that white wire gets "taped back" after C104, knowing that would have saved me running a new wire all the way from my brake switch to my camper shell CHMSL ... I'm gonna have to look at my truck cuz my wiring from that connector to the rear is still factory for now, I would swear there was no white wire at all in that harness.

Click to expand...

I saw the same thing. I didn't see any taped back lead on C104.