Trying to Track Instrument Cluster Power(?) Issue

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drag sgt

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Vehicle: '98 K2500 Suburban Diesel

Yesterday I noticed that the 'wait to start' indicator on the instrument cluster (IC) wasn't coming on when the key is cycled. At first I thought it was a glow plug relay issue, but after some investigating, I noticed that several other indicators, notably the DRL, Battery, Water in Fuel, STS, and SES lights were also not coming on when the key was cycled.

I have swapped all my cluster bulbs to LEDs so I thought maybe several happened to go out. Upon pulling the cluster and testing though, I found that all bulbs worked fine when probed individually, as well as when power was applied to the PCB and cluster ground (so no bad traces). I even swapped bulbs and found that the same ones still weren't lighting when plugged back in to the dash. As an extra precaution I tested all fuses with no issues.

I next pulled up the IC pinouts diagram from this post and tested the dash pins which matched the non-working bulbs (1, 17, 18, 19, 20, 21, 23). On each pin I found that I had no power on ignition cycle, so I'm guessing the issue isn't with the cluster.

I'm looking at the service manual but am having a hard time reading the B/W diagrams, or finding some kind of test. All other indicators and gauges work fine--it's basically everything in the top-left corner of the IC.

Does anybody have access to some color-coded diagrams that are better than what's in the service manual? It's dang near impossible to look back there for chaffed wires so I'm trying to figure out if there's a commonality among these wires (e.g., common ground) that I can look at before resorting to more drastic actions.

Thanks
 

mwilliams55555

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I have a 95, diesel automatic cluster sitting on the self, got it because I needed a unbroken clear front panel
 

drag sgt

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I guess I never came back and wrapped up my own thread, but I did eventually fix this issue. After staring at it for a couple days. I realized I was applying my test power/grounds to the opposite side of the board traces, meaning I was orienting my LED sockets the reverse of the actual flow of power once hooked back into the dash. Once I flipped them all around, all the lights worked again.

However, I just recently swapped my cluster bulbs back to old-school bulbs, for a couple reasons:

1) I couldn't full adjust the brightness of the cluster down due to the resistance changes, leaving it way too bright for night driving. During a winter storm last spring it was like a sensory overload.

2) Also probably due to the reduced resistance of the LED bulbs, several warning indicators never fully turned off. For example, my 'Wait to Start', Security, SES, and Air Bag warning lamps all had a very faint glow, which was again most noticeable at night. I tried a couple other led bulbs in my pack thinking it might be a short, but it was never resolved. Once I put an incandescent back in as a test, the faint glow was gone. I only left the turn indicators as LEDs, but that was more because I ran out of 74 bulbs.
 

AK49BWL

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Yeah that ABS and airbag light drivers will fault code a bad bulb if you put anything but an incandescent in its place unfortunately - same is true of the Passenger ABS selector switch, put LEDs in mine and the dash indicator never went out again until I gutted the whole system for a 94 interior lol. The only good way to rectify the backlight dimmer issue is to use a PWM-based potentiometer. I put two in mine, one for the backlights and one for the LCDs. I've gotten used to the very faint glow of the SES light to the point of actually liking it lol - it tells me when the PCM is still active after I shut the truck off (I also routed courtesy power to the cluster for indicators after shutdown - the BCM shuts that circuit off after 10 minutes).
 
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