97 silverado, 5.7, 2wd, 130,000 mi, instrument light out


#1

My son was driving last night and his dash lights suddenly went out. The warning lights come on when starting the truck but he cannot see the gages after dark. Fuse #4 is good which the manual said controlled the instrument group. Can someone tell me how to locate the lamp or other ideas as to what might cause this. As far as I can tell everything else looks good.


#2

It could be the rheostat that controls the brightness of the dash lights. I lost all the dashlights on a 1990 Ford Aerostar and, after checking the fuses, this turned out to be the problem.


#3

First thing is check the rheostat (dash dimmer basically) and make sure it has not positioned to cut the dash lighting off. After that the output of the rheostat (should be part of the headlight switch) should be checked. If it’s dead there then the entire switch should be replaced.


#4

Headlight swtch works fine. Tried moving rheostat back and forth several times but not even a flicker of the dashlights. Before replacing the rheostat, it seem best to check the lamp itself. I have looked under the dash but do not see the bulb. Does anyone know where it’s at and the easiest way to remove it?


#5

I think that there is more than one bulb for the dash lights. If you lost all the lights on the instruments, it would be rather unusual for all the bulbs to go out at the same time. You may want to check to be certain that the tail lights are working. In many vehicles, the tail lights are on the same circuit as the dash lights.


#6

The rheostat is a separate circuit in the headlight switch. It is possible for the HL switch to work fine and the rheostat part may be burned out. Headlights and park lights will work fine but the dash lights will not.

If the rheostat is faulty then the entire switch must be replaced or the rheostat can be bypassed at the switch to allow dash lighting to remain full bright at all times.


#7

The comment about the rear lights being on the same circuit reminded me that i had to clean the connector where the rear lamps plug in a few months ago. If I can get my son to slow down for a while I will disconnect the connector to the rear lamp assembly and see if the dash lights come back on. I porbably need to replace the connector board assembly. Last time the problem was low voltage to the rear lamps caused by carbonization on that assembly. Thanks for the help.


#8

More information but still same problem, dash lights and parking lights not working. I replaced the plastic cards in the taillight assembly where the rear blubs plug into. Next I replaced the fuse #9 which is for the parking lights. Everything worked for a few minutes and then the #9 fuse blew again. The wiring that I can see near the rear bumper and the taillight assemblies looks fine. I’m about out of ideas and any help would be appreciated.


#9

Now comes the real fun!! You have a short circuit somewhere. Typically, these are caused by damage of some kind to switches or wiring. This circuit is hard to determine, because the wiring spans the length of the truck, from cab to tail. I’d test the obvious switches for problems, then move to thw harness connectors. This truck should use GM Waether-pak connectors, so damage may show up as partially melted connectors. This happens when moisture causes corrosion, and the resistance of the connection goes way up. The heat from the resistance causes the connector to melt. Also, has this truck been in any accidents? Accident damage can extend to the wire harness, exposing wires. Good luck.


#10

I had considered first disconnecting the connector to the drivers side rear light assembly, then the passenger side to try and isolate the problem/short. Are there other connectors or things that can be disconnected to further isolate/locate the problem? What is the best way to get to the dash light rheostat and headlight switch where it can be reached. I don’t expect this weekend to be fun but hope to find the problem without causing another one. Worked electronics in service years ago but can still follow the schematic in the Haynes manual. It’s locating the wire or physically removing dash parts without breaking anything that is the problem. Could be in the door lights too.


#11

You keep mentioning the rear of the truck, so I assume that the tail lights as well as the parking lights and dasboard lights aren’t operating. Do you have a connector for trailer lights? This could be the cause of the short circuit that is blowing the fuse.

I had a short in a trailer connector one time that caused all kinds of problems. The dashlights and tail lights first failed. I switched on the emergency blinkers and that fuse blew. The turn signal fuse blew. By the time I reached home after 80 miles, all I had left were the headlights.


#12

Looking at some info it shows that fuse #9 goes to the lighting switch and rheostat. The output of the rheostat then passes though fuse #14, the illumination fuse and on to the dash lights along with a lot of other areas. There are 6 bulbs in the dash to provide light to the instuments. I suggest you use a test light probe or meter to check for voltages at the points mentioned.

Fuse #9 also feeds the rear clearence lights, headlight system, and interior lights. They splice together at S210 and are brown wires, but I don’t know where the splice is. I suspect it is near the dash area. Hopefully finding the short problem will clear the dash light problem also since they are tied together.

Triedaq’s thought about the trailer connection is very good since that is a common trouble area and there is a brown wire going to it.

This is a case where having a factory service manual to help locate the trouble is very helpful since it will tell you where to find things like the splice. I think you would be wise to get one to help find the trouble. It will pay for itself with this one repair. Ebay is a good place to find used and new manuals at a discount price if you don’t want to pay dealer prices for one. Armed with a good manual and a test light probe you should be able to locate the trouble without much problem.


#13

I know I have my work cut out for me this time. There is not a trailer connection that I know of. I have looked under the rear bumper and there are connectors at each tail light and in the middle where the wires go to the liscense plate. I did disconnect and inspect all three. They loked normal, nothing looked unusual, melted, or felt brittle. The brake lights and turn signal lights work. I know the rear parking lights, the instrument (all dash lights), and the interior door lights(for door switches) are out.


#14

I think once you find the short you will be back to normal for all the areas having trouble though some dash light bulbs may be burned out. There are devices on the market, that use a tone I think, to help locate shorts.

You can also substitute fuse 9 with something like a headlight bulb. It will keep the current to a safe level. You may be able to find the short this way. Where ever the short is there will be zero voltage at that point. You may be able to see a faint light on the legs to the bulbs that don’t have a short on them due to the wire resistance between them and the short. Hopefully the short is near one of the rear lights. This may not work to well but you could try it and see.


#15

My son and I traced the wiring from the rear lights to the engine compartment and also looked at the wiring around the left foot of the driver and where it passes to the cargo lights. We saw no bare wires. My best guess is that the connectors from the wiring harness to the rear lights and a couple others near the rear bumper are dirty. The fuse holds for about 10 minutes after I disconnect them. My son went ‘mudding’ about 6 months ago. Is there something that will clean the connectors without doing damage to the plastic? Some of the holes are too small to get brushes inside to clean them out. I have some diaelectric grease but should it be put only on the contact and not allowed to touch an adjoining contact?


#16

Found the problem last weekend. One of the front parking lights had a broken filament that bounced around and at times touched a second filament and blew the fuse. I had started at the rear because of a previous problem and thought that I was on the right track when the fuse would hold after cleaning and reconnecting those connectors. Finally disconnected the cable going to the rear at the firewall and the fuse still blew. Then noticed one of the front parking lights seemed too bright. Next time would be easier to check all of the bulbs on the fuse before looking at the wiring. Thanks for the help. Kept me from giving up.


#17

Thanks for the update Klt and glad to hear you got it fixed.