Dash lights out

[riv1973]

Hi all!
got another new issue see discovered with our 1988 blazer.the dash lights are out. The gauges all work except for the oil pressure gauge but I think that is the sensor. If I turn the headlight switch I dont get any interior lights. Fuse is good and replaced ( the 5 amp one) and there does not seem to be any other obvious shorts. Is tt possible the headlight switch is bad? Could it be the Instrument cluster?

any ideas on how to track it down? I thought it was strange that none of the courtesy fixtures have bulbs in them. I wonder if one of the has a short. But wouldn‘t the fuse be blown.
any help would be appreciated

 

[ZooMad75]

Before you fire off the parts cannon at the truck did you twist the headlight knob? The dimmer for the instrument lights is housed within the headlight switch. Turning the knob counterclockwise will cause the dash lights to go bright, clockwise will dim them.

That dimmer adjustment is one of those hidden in plain sight deals. Anybody that is used to the modern way of dimming the dash with a separate adjustment wheel or dial would completely miss the knob turning on a square.

 

[dyeager535]

The door jamb switches are pretty problematic. As I recall the interior lighting is a fairly complex circuit, there is probably a good reason the bulbs are out.

I second not throwing parts at it, but I'd try a bulb in one of the fixtures and see what happens.

Gauge is probably a different issue, but I wouldn't blame the switch yet.

 

[riv1973]

i tried the turning of the headlight knob. nothing. i was going to get a bulb and see what happens with the fixtures. i think that sending unit for the oil pressure gauge is out and i am going to replace that. i am going to inspect each light and see if one pops when i install it and maybe that can be the short. there was an after market radio in it that my son removed. it might be the source of the dash lights being out. i am going to search for a short tomorrow.

if the dash was bad ( it seems to be the old integrated circuit kind), would all the lights be out on all the gauges or would the lights be out on one individual gauge.

so what is the issue with the door jam switch? do they short out? not work? or cause the interior lights to stay on. that could be why i have no bulbs in the fixtures.

john

 

[dyeager535]

The door jamb switches tend to get rusty, I assume at some point they can fall apart. Plus the wires arent a positive connection to the switches, so if the wires pop off, I assume they can complete the circuit and never go off.

I can't recall what an '88 cluster looks like on the back. GM changed the design later on so that all the power and grounds (for the most part) are shared. So if there is a power or ground issue, a lot of stuff should be screwed up. However, the gauges still connect to the flex circuit in a pretty hokey way, if someone has been into the dash, they could easily mess it up.

If just one light/gauge, it could be as simple as a bad bulb.

 

[kennyw]

Door jamb switches typically fail in the "off" position. They function by grounding the circuit. The wires do not fall off easily, I actually find them difficult to remove when I try to save both the switch and wiring from a parts truck.

 

[Wes Harden]

I have had several bad new head lamp switches, they worked the head , and running lights but not the dome lamp. I took one back to parts store, and a dvom. I test 3 other switches they had in inventory, all had same flaw. This was awhile ago, but once a bad engineering drawing get used.....
I would test the switch before the instrument cluster, less risky the plastic cluster.
It would not surprise me at all if the dimmer rheostat was warn out and open.

 

[riv1973]

I will get a new head light switch. I am also getting some light bulbs. I will start there.

So the door jam switch fails and falls apart or just fails internally so they never trigger the dome Lights? It seems someone most likely pulled the dome lights because they may have been on all the time?

Also could there be a bad ground on the radio portion and this could be causing the interior dash lights nkt to work?

Does anyone make an under the dash wiring harness for these trucks?

Would the bad ground cause other problems with the dash?

The dash is also like a circuit board. All things plug into it. I fee that this is dash light problem is something on the lighting side. Not a bad ground but that is a feeling.

And the headlight, marker lights, high beams and all exterior lights work. Just dash lights.

Thanks again guys!

 

[dyeager535]

I have had several bad new head lamp switches, they worked the head , and running lights but not the dome lamp. I took one back to parts store, and a dvom. I test 3 other switches they had in inventory, all had same flaw. This was awhile ago, but once a bad engineering drawing get used.....
I would test the switch before the instrument cluster, less risky the plastic cluster.
It would not surprise me at all if the dimmer rheostat was warn out and open.

That made me remember I got my hands on a brand new aftermarket headlight switch at one time, and all the ceramic (?) Material from the rheostat came crumbling out.o


With a voltmeter you can check the output of the existing light switch. IIRC you have to physically ground the switch body if testing with it disconnected from the dash however, as it uses the dash to ground.

 

[fordsucks!]

The headlight switch, when you turn it clockwise then the dash lights get brighter. At the very end of the turn, you feel a click and then the dome lights are supposed to turn on. Are you able to turn the dimmer clockwise and have the dome lights turn on at full clockwise?

 

[riv1973]

i just replaced the dome light bulbs last night. it came with none. i turned it click wise and felt the click but i didn't have the bulbs in yet. i am going to replace the head light switch and see what happens

 

[Drewfrazier]

I have a similar problem with my ‘72. Headlights function but turning the dimmer reverses the turn signal blinker on the dashboard and high beam indicator. Only the heating and defroster cluster is lit. Go figure.

 

[Clark75K5]

Check to see if the fuse retainer clips for that circuit haven't become brittle and broken off - I had to replace 3 of mine.

 

[88Silverado]

I uploaded the wiring diagram for the internal lighting. The door switches are a little plunger type switch. Occasionally I have to slightly "twist" the button back and fourth to achieve a ground to turn on the dome lights. They are pretty poor switch. In addition, the dome light tabs do become rusty or oxidized so cleaning them first with some scotch brite or steel wool is a good idea when replacing the bulb.
The lighting on the back of the cluster is a flex circuit so be careful. The lights will sit in a small plastic holder that is "twisted to lock" into place. Even after replacing all my dash lights, some come on and off as they feel due to the poor design. The wiring is pretty basic but chasing it down is not all that easy. If you are going into the back of the cluster, remove the dash pad first as this will help access to the speedo cable that will need to be disconnected to pull the gauge cluster forward.

@dyearger535 glad to see you are still around.

 

[riv1973]

thanks guys! i think maybe it could be the lights out on the dash since all the other stuff works ( interior lights, head lights and such). i will order them up! thanks for the wiring diagram!