I'm trying to track down why a few of my dash lights aren't working. The entry door, the parking brake, and the low fuel indicator lights don't seem to be working. Has anyone worked on these before? I see the door jamb switch and will be testing for power. I've read that the parking brake switch is located on the bracket bolted to the cab floor and will be checking for 12v there as well. I haven't found any information on the low fuel indicator light though. I'm assuming this is a matter of resistance on the circuit but some info here would be appreciated. I'd like these indicators to be in working order.
Dash warning lights
- Thread starter hylomatt
- Start date
Just by jumpering the switches you mentioned previously.
Do any of the tell tale lights work?
Mine is a 78 so likely different than yours, but I believe mine gets power from the horn relay via the 'key in ignition' switch.
Does you horn work? Does your key buzzer work?
Do any of the tell tale lights work?
Mine is a 78 so likely different than yours, but I believe mine gets power from the horn relay via the 'key in ignition' switch.
Does you horn work? Does your key buzzer work?
Matt,
The bulbs are a very common number and mounted in little twist in sockets. If you get a hand back there, you can feel the little blade that is the handle.
Do you have the whole schematic there? It helps if you can lay it out on the dinette table.
The low fuel indication comes from a module that is probably loose behind the instrument panel. That attaches to the gauges at the selection switch.
Matt_C
The bulbs are a very common number and mounted in little twist in sockets. If you get a hand back there, you can feel the little blade that is the handle.
Do you have the whole schematic there? It helps if you can lay it out on the dinette table.
The low fuel indication comes from a module that is probably loose behind the instrument panel. That attaches to the gauges at the selection switch.
Matt_C
@kbeefy Your'e right, bypassing the switches will do the job. I know that 2 of my lights work. The "switch to travel" light works as designed and my low fuel light is always on, no matter the tank level. My horn works (except for once after a lot of rain). My key buzzer does not work.
@Matt Colie I have the schematic from the owners manual. Every time I reread it, I start to notice more data that from before but I don't see this circuit so far. Is that the schematic you're referring to? I've had my fuel selector switch out of the dash before and there was no module piggybacked onto it. Just the switch and its wires.
@Matt Colie I have the schematic from the owners manual. Every time I reread it, I start to notice more data that from before but I don't see this circuit so far. Is that the schematic you're referring to? I've had my fuel selector switch out of the dash before and there was no module piggybacked onto it. Just the switch and its wires.
It's on that, between cruise control and instrument cluster.
It looks like it gets it's signal straight from the fuel level signal on the selector switch, as @Matt Colie mentioned. That 'module' probably reads the fuel level and closes a contact when the resistance from the fuel sender gets down to a certain level.
It looks like it gets power from the instrument circuit and grounds at the common panel ground.
I assume your fuel gauge works and the low fuel light doesn't change with tank selection?
That would lead me to believe that module has failed in the closed position or theres a short to ground on the white wire.
If you wind up with the rear dash cover off for bulbs try finding and unplugging that module.
I think Matt was saying it's wired to the switch and stowed loosely in the area, dot directly connected to the switch.
Since other lights are working you have power, that leaves bulbs, wiring and switches. And the contact traces and bulb holders, but I'd start with bulbs. It's really easy once the rear panel is off. Mine cracked a bit taking it off, be careful.
Matt_M,
It looks like you have the correct diagram for a 73. The module is just a thing that looks like a bulb could plug into it, if it is like mine. It just has the four leads coming from it.
Delco instruments of that period were 0~90Ω. With 90 at the high/full end.
The module gets power and ground from the same junctions that feed the rest of the dash.
Matt_C
It looks like you have the correct diagram for a 73. The module is just a thing that looks like a bulb could plug into it, if it is like mine. It just has the four leads coming from it.
Delco instruments of that period were 0~90Ω. With 90 at the high/full end.
The module gets power and ground from the same junctions that feed the rest of the dash.
Matt_C
@Matt Colie oh I think I saw that previously and wondered why/where a bulb should be located. It was just hanging there.
It just measures resistance? And I can test it by adding or removing resistance in the circuit? That's how I would be able to tell if it is working or has failed?
It just measures resistance? And I can test it by adding or removing resistance in the circuit? That's how I would be able to tell if it is working or has failed?
Heres a pic....
I was thinking it might be the silver can with the arrow pointed at it, but it sounds like @Matt Colie would know better than I.
Again, mine is a 78 so likely somewhat different than yours.
I was thinking it might be the silver can with the arrow pointed at it, but it sounds like @Matt Colie would know better than I.
Again, mine is a 78 so likely somewhat different than yours.
Speaking of dash lights...
There is no illumination for the boost or fuel selector switch on mine. Should there be?
There is no illumination for the boost or fuel selector switch on mine. Should there be?
Remove your dash cover and give each bulb socket a twist, often times the connection just gets oxidized and moving the sockest is all it takes to get the bulbs working again.
The low fuel module is a little circuit board with four wires going to it, it usually just floats arounf under the dash above the brake pedal somewhere.
The silver can is the time delay for the "Set Level To Travel" light.
@kbeefy In my '73, there is no illumination for the fuel and battery switches either.
@Don Jaksa I have not addressed this yet. I have purchased the Alt safety wire but have not installed it yet. https://www.gmcrvparts.com/product-p/gm7-2541f.htm
@JSanford okay, I'll give the bulbs a twist and see if this changes anything as well as look for this floating circuit board.
@Don Jaksa I have not addressed this yet. I have purchased the Alt safety wire but have not installed it yet. https://www.gmcrvparts.com/product-p/gm7-2541f.htm
@JSanford okay, I'll give the bulbs a twist and see if this changes anything as well as look for this floating circuit board.
