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I am going to start some troubleshooting for Instrument Panel lights and Fuel Gauges to find out what parts I am going to need to solve this problems.
I dont find the Constant Voltage Regulator in the Wiring Diagram and therefor dont know if all gauges and lights should have 5V or just the Gauges. For now there's no light in the Instrument Panel and Fuel Gauge is not working. I am also going to check resistance in Fuel Sender Unit.
Temp Gauge, Turn Signal Indicator, High Beam Indicator and Engine Control Lamps are working just fine. Thanks!
OK I don't know your truck but all cars/trucks I have worked on the 5v is only for the fuel, temp and maybe oil psi gauges.
The dash lights get a full 12v thru the head light switch.
Have you checked ALL fuses? You may want to pull all of them and clean the ends and holders as they can get a thin film of corrosion and will not let power pass thru but look good. I have had old cars/trucks had this happen and once cleaned all worked as should.
With that said if only the fuel gauge is not working to see if the wiring/gauge is the issue or the sender.
Remove the wire from the sender and with the key on ground the wire. If everything is good the gauge should move to full when grounded and drop when removed.
If so the sender is bad and will need to be replaced, don't forget the O ring gasket.
If it does not move you will have to do more digging. See if there is a plug closer to the gauge and ground the wire there. if still noting move closer to the gauge.
If you pull the gauge I think there is a way to test it using a "D" cell batt. (1.5v) to see if it moves.
For dash lights first try and rotate the head light switch like you are dimming the dash lights and turning on the inside light.
I have found the dimmer rheostat gets a green funk and the dash lights do not light up. Some times rotating it will work for a little time but the switch should be replaced.
If that does not show anything you will have to pull the light switch and test to see if power is leaving the switch and go from there out to the bulbs.
If you have the switch & gauge cluster out might be a good time to replace all the bulbs. LED's are nice but some do not dim so check before you go that route.
I had no instrument lights on my 79 and it turned out that those blue diffusers over the lamps were blocking all the light, removed them and now the instrument lights work, of course, not as pretty as when they ar blue
OK I don't know your truck but all cars/trucks I have worked on the 5v is only for the fuel, temp and maybe oil psi gauges.
The dash lights get a full 12v thru the head light switch.
Have you checked ALL fuses? You may want to pull all of them and clean the ends and holders as they can get a thin film of corrosion and will not let power pass thru but look good. I have had old cars/trucks had this happen and once cleaned all worked as should.
With that said if only the fuel gauge is not working to see if the wiring/gauge is the issue or the sender.
Remove the wire from the sender and with the key on ground the wire. If everything is good the gauge should move to full when grounded and drop when removed.
If so the sender is bad and will need to be replaced, don't forget the O ring gasket.
If it does not move you will have to do more digging. See if there is a plug closer to the gauge and ground the wire there. if still noting move closer to the gauge.
If you pull the gauge I think there is a way to test it using a "D" cell batt. (1.5v) to see if it moves.
For dash lights first try and rotate the head light switch like you are dimming the dash lights and turning on the inside light.
I have found the dimmer rheostat gets a green funk and the dash lights do not light up. Some times rotating it will work for a little time but the switch should be replaced.
If that does not show anything you will have to pull the light switch and test to see if power is leaving the switch and go from there out to the bulbs.
If you have the switch & gauge cluster out might be a good time to replace all the bulbs. LED's are nice but some do not dim so check before you go that route.
Good luck
Dave ----
Thanks a lot both of you guys!! I didn't knew you could check the sender this way. I will check sender, fuses, wiring, bulbs, Head Light Switch and ground. I was thinking of the printed Circuit or Instrument Regulator but when Temp gauge is working this is probably not the answer.
I dont know why I dont find the Instrument Regulator in the Wiring Diagram, only a "Resistance Wire" to the Inst. Panel.
The dash lights are powered through a rehostat that is part of the headlight switch. The voltage will vary from 12 volts to nearly zero. That is if it's working.
It's not unusual for the wiper to get crusty or just plain fall off. Or for the wound wire resistor to fall apart or hop out of the groove. If everything is intact, try cleaning it with contact cleaner. I use DeXoit but most anything that doesn't leave behind a flammable residue will work.
The gauges are the only things powered by the I.V.R. It provides a steady and mostly 5 volt source so the the gauges don't track your charging system as it wanders around between 12 and 14.7 volts.
Yes, link works and helps a lot! Thanks!
Does all current (for Gauges and instrument lights) go through the printed Circuit or is it a mix between the Circuit and Wiring?
Matt, if your temp gauge is working, your cluster voltage regulator is good.
Often the back of the cluster starts to crumble & this allows the bulb holders to lose contact, then the lights don't work. Very common for this to happen at the holes that hold the cluster illumination lights, the added heat from the bulbs being on for long periods seems to speed the deterioration.
All the current to the gauges & lights goes thru the printed circuit. The power gets to the cluster thru a large plug on the back, that plug is part of the main wiring harness.
Thanks a lot everyone for excellent explanations! Now it's a lot easier to start troubleshooting and find out what I will need to fix lights and Fuel Gauge.
I had the crumbly instrument cluster in my 77. First time I "fixed" it, I superglued the light sockets to the Mylar. That actually worked.
Eventually, I got a cluster out of an 80s econoline. Works great.
When I first bought the truck, the dash lights didn't work at all. As I was driving home, in the dark, I rotated the **** back and forth. Eventually, the rheostat cleaned up enough that the lights work in most of the arc.
I also replaced the inner two bulbs (the actual illumination bulbs for the cluster) with Sylvania LEDs. They're super bright, and they ARE dimmable
Thank you PapaBear. I just installed qty 2 of the Sylvania '168' cool white LEDs in my instrument cluster and WOW, they work fantastic. Mine were so dim, I could barely read a gauge. Per the advise, I was able to reach the center two sockets; (nearest the speedometer cable); without removing the instrument panel, by laying on my back with head on the center floor hump and reaching up with my right hand into the rat nest.
It did not visually appear possible to do this, and I had tried a few times prior to reading this thread; but if you get in this position, you find there is enough room to get your hand up in there, fingers onto the sockets, and easily remove them within a minute! Thanks again to all.
Since this is my first post; I will admit to realizing I have been visiting this site for nearly three years, and always find great ideas. I finally signed up!
03-15-2017, 05:03 AM
