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Gauge light replacement

Discussion in 'Tech Discussion' started by thecantaloupeman, Oct 12, 2019.

  1. thecantaloupeman

    thecantaloupeman Full Access Member

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    Has anyone replaced their gauge lights that remembers the size of the lights that you need. My gauges look like they are glow in the dark at night instead of being brightly lit. I thought about LEDs but I am not sure if thats safe to replace regular bulbs with LEDs. They also might look weird because the gauges will be lit up white instead of yellow like they were originally. As long as they are bright enough to read I'm happy.

    Will replacing the bulbs make them any brighter? Hoping someone who has done a repair like this can help me out. Thanks.
     
  2. 1987 GMC Jimmy

    1987 GMC Jimmy Automobile Hoarder

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    168 SilverStar is what I’d recommend. If you can’t get your hands on enough 168s, 194s will be fine. The 168 is a slightly more powerful bulb, and the SS bulbs have a crisper luminescence compared to basic incandescents. I’m not big on LEDs except maybe for cabin lighting. They’re safe to use, but the rheostat dimmer can’t dim them. It’s either on or off.
     
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  3. chengny

    chengny Full Access Member

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    Before you tear into the instrument cluster, check the rheostat that varies the intensity of the dash lighting (as well as the heater control panel and radio backlighting). The rheostat is integral to the headlight switch.

    First look at the heater control panel light (just 1 lamp) and the radio lamp - if still installed. If those components are not lighting up as designed, the problem most likely is the rheostat. On the other hand, if they are nice and bright, first check is that the connections at the common ground bus bar are clean and tight. It is bolted to the cab interior wall up above the parking brake. They're like all spliced together into one common lead but check the connectors anyway.

    Grounding block.JPG

    What happens with the rheostat is that over time the movable contact begins to lose good contact with the variable resistance (looks like a spring shaped in a circle). Or sometimes either or both of the surfaces can become oxidized. In either case, resistance increases across the rheostat and consequently the current flow to the controlled device drops. In this case, the lights grow dim - kind of like me.

    IMG_0481_470x.jpg

    Also be sure to check that the fuse - labeled PNL LTS is tight and clean in the clips. I believe you still using the AGC style fuses and they have a tendency to loosen up over time.
     
  4. Craig 85

    Craig 85 Full Access Member

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    168 are 3 watts, 194's are 2 watts. I recently replaced all my dash bulbs. It had 168's from the factory but the store didn't have enough, so i got some 194's. They were too dim. I changed them all to 168's
     
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  5. thecantaloupeman

    thecantaloupeman Full Access Member

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    So is the rheostat I need to check behind the headlight knob? I don't think my heater light and radio light are bright either, so I may need to check this. I will also give those grounds a look. Thanks for the info.
     
  6. chengny

    chengny Full Access Member

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    Yeah. Remove the H/L switch from the dash - yours will look like the one shown below. First, reach under the dash and - while depressing the shaft retaining button - remove the switch rod and knob.

    s-l1600 3.jpg

    s-l1600.jpg

    The switch will be secured to the steel dash with a round nut like this:

    s-l1600 2.jpg

    Problem is; the nut is sandwiched between the steel dash and the bezel. So, to get a pair of Channelocks on it requires pulling the bezel away from the dash. I don't think it needs to completely removed - it has enough flexibility that you can get behind it by releasing just the screws on the LH end. Unplug the harness and unscrew the nut. The first few threads have to be backed out by rotating the nut. But after the little locating tab is clear of the notch in the dash, you can just spin the body of the switch.


    You'll figure it out. When you have it in hand, inspect the rotating tab and the wound resistor.
     
  7. MisterB

    MisterB Full Access Member

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    Yup. Just rebuilt my cluster and replaced all lights with 168's. While I was in there, I replaced the heater bulb and the washer bulb. Here's a Pic from my test ride before I put the dash trim back on.

    Turned out really nice, and I can see it easily [​IMG]

    Sent from my SM-N975U1 using Tapatalk
     
  8. 78C10BigTen

    78C10BigTen Full Access Member

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    I put 6k white leds in mine and i prefer them. Not sure where the pic went
     
  9. ShortBus

    ShortBus Member

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    THe only gauge that lights up on my dash is the fuel gauge. The speedo comes on but only very dimly. No other dash lights come on except the left blinker indicator stays lit if the lights are on.
     
  10. MisterB

    MisterB Full Access Member

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    You might need a new circuit board. May as well do a total rebuild of your cluster while you have it out. Clean it, replace the bulbs, paint the needles, and replace the clear plastic lens

    Sent from my SM-N975U1 using Tapatalk
     
  11. ShortBus

    ShortBus Member

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    That's what I've been figuring on.
    I also want to add a factory tach since I have a manual tans.
     
  12. MikeB

    MikeB Full Access Member

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    Yes, 168 bulbs are the way to go. But more importantly, you'll need max voltage to the instrument cluster. Depending on the age and condition of your wiring harness and connectors, I wouldn't be surprised to see 12.5 volts or less with the alternator putting out 14.2 volts.

    Unfortunately I didn't take any pictures, but when i installed a new wiring harness I put some shiny aluminum tape inside the cluster housing around the gauges. It made a noticeable difference. I used the very thin tape that's more like mylar than aluminum foil. You can get it at hardware stores.
     
  13. thecantaloupeman

    thecantaloupeman Full Access Member

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    W
     
  14. 1979k10

    1979k10 Junior Member

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