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Newbie here, need advice on troubleshooting instruments gauge lighting problem

Timsar

Timsar

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SF / N. Kali
74 K5.
None of the light bulbs in the instrument panel light up.
Checked:
1) fuse, ok
2) replaced main light switch.
3) replaced all lightbulbs
4) checked the flexible printed circuit on the back of the panel, looks ok. Ordering a new one anyways, because of its age.
5) need to check the lightbulb socket connection to flexible PCB.
5) ordered electrical. Wiring diagram to follow wires
6) ordered a 12v power supply to trouble shoot the whole gauge assy, before putting it back together.

Am I missing any steps or items?
 
The ground. Gotta check for a good clean ground to complete the circuit.
 
Have you checked power and ground at the bulb sockets with a meter?
 
90% of dash light issues are typically connection between the socket tabs and the circuit board. I find the best way to deal with them is to pull the whole cluster and clean everything. Then slightly bend the socket tabs to increase pressure on the currie board connections during reassembly.
 
I hit them lightly with some fine emery cloth, the socket terminals.
 
Timsar said:
74 K5.
None of the light bulbs in the instrument panel light up.
Checked:
1) fuse, ok
2) replaced main light switch.
3) replaced all lightbulbs
4) checked the flexible printed circuit on the back of the panel, looks ok. Ordering a new one anyways, because of its age.
5) need to check the lightbulb socket connection to flexible PCB.
5) ordered electrical. Wiring diagram to follow wires
6) ordered a 12v power supply to trouble shoot the whole gauge assy, before putting it back together.

Am I missing any steps or items?
Click to expand...
I have been rewiring a 88 Blazer that had an engine bay fire. I have the complete 1988 engineering drawings. Tell me what circuit you want a photo of the that page. If you are at a stop you may want to piggy back new power lead ground wire and a separate fuse and switch. Dan.
 
Don’t forget the dimmer in the headlight switch. Power is going to come from that to feed the instrument lights. That is a common fail point on all of these. If you don’t have power coming from that the lights won’t come on.
 
Yes i went through 3 or 4 brand new switches at the part store. After the first one had no continuity through the rheostat, I took my ohm meter, and pull knob to the store and tested every one they had on the shelf. All failed. Wasn't Autozone or Oriellys either was real parts store. That truck still needs a good light switch.
 
First of all, Thank you everyone for your suggestions. I spent the past 2 days trying to trace wires and trying to figure out what's going on.

The flexible PCB is ok, I connected a 9v power supply and all the individual bulbs light up. So the lamps & sockets are good.

Next I connected the main Wiring harness to the PCB and still no main dash lights, By turning on the main headlight switch and playing with know. The main interior lamp, located under the dash does come on and dims. The turn signals work, so does the flasher. BUT no instrument light.

The fuse has power and it does come all the way up to the harness.

Only unknown is I don't know for sure which wire in the main connector supplies power to the instrument panel flexible circuit.

I traced the lamp socket on the flexible circuit to port # 2 and 3. But the corresponding pin on the harness has no power!!

I have bought nearly every manual, from official GM service manual to a Reprint of all the electrical diagram, BUT the wiring harness connector is not listed.

Will continue tomorow.
 
kennyw said:
90% of dash light issues are typically connection between the socket tabs and the circuit board. I find the best way to deal with them is to pull the whole cluster and clean everything. Then slightly bend the socket tabs to increase pressure on the currie board connections during reassembly.
Click to expand...
Thanks for the tip. I did that. The connections are good
 
Miss Piggy said:
I have been rewiring a 88 Blazer that had an engine bay fire. I have the complete 1988 engineering drawings. Tell me what circuit you want a photo of the that page. If you are at a stop you may want to piggy back new power lead ground wire and a separate fuse and switch. Dan.
Click to expand...
Hi,
I need the drawing of the harness connector that plugs into flexible circuit.
 
Here are some pics to put things in prescriptive. I think I will try to splice power into back connector trying to isolate. Next is perhaps the main light switch which already has been replaced and it does turn on main headlights, interior light and dim function works too.

20230903_112937.jpg

20230903_112959.jpg

20230903_113144.jpg

20230903_113209.jpg
 
By splice I hope you mean jumper. There is no positive benefit that comes from ruining the wires jacket.

You need a multimeter. It's super easy. I want to say on the late stuff the light wire was yellow. You could probably look at the headlight switch and the IP connector and see which goes up that way. The multimeter will ensure that wire isnt compromised. And verify that it's power not ground that is lacking at the bulb while everything is connected.

Your wiring diagram is probably here: http://67-72chevytrucks.com/vboard/showpost.php?p=5621043&postcount=1

Do not use any except the GM one for your year. Sometimes you can get away with another year if it's close enough, but gauge wiring changed at least three times throughout the run (not counting options, idiot lights, diesel, and other variations to "standard" gauge wiring) so just assuming a random year, or a Haynes manual will be correct, may lead to frustration and damage.
 
Sorry if this has been mentioned and checked. The instrument lamps have their own fuse, has this confirmed good ? what color is the wire that you think should have power and doesn't and which cavity in connector ?
 
Lt green from rheostat feeds 5amp fuse in block and gray wire to feed lamps in the IP. Sounds like the LT grn has power from rheostat since other lamps work.
need to check that fuse, and see if gray wire at IP plug has power.
 
Another thing that just occurred to me and should have remembered the 1988 truck and the K5 are not the same. Was a real bitch in 1988 when they change everything for the light trucks but not the K5, suburban, the shop manuals are confused. I always used a 1987 for 88 k5 burbs. 1989-91 are different as well.
 
Wes Harden said:
Another thing that just occurred to me and should have remembered the 1988 truck and the K5 are not the same. Was a real bitch in 1988 when they change everything for the light trucks but not the K5, suburban, the shop manuals are confused. I always used a 1987 for 88 k5 burbs. 1989-91 are different as well.
Click to expand...
You need the RV manuals. I just uploaded all of them to the forum but they are not public yet.

However, it can be downloaded here.
www.mediafire.com

ST_350_88_1988_Chevrolet_GMC_Light_Truck_Wiring_Manual_Complete_11x17

MediaFire is a simple to use free service that lets you put all your photos, documents, music, and video in a single place so you can access them anywhere and share them everywhere.
www.mediafire.com
 
The ends of the copper circuit on the pcb at where the harness plugs in is extremely fragile and can delaminate from the plastic. Repeated plugging and unplugging the connector into the cluster can and will pull that copper from the plastic.

I wouldn’t be surprised if the circuit for the lights folded back and wasn’t making contact with the terminal on the plug.

But your idea to id the specific terminal on the plug is the right one. If you can confirm power to that terminal and already confirmed the cluster pcb is ok with the 9v power supply you should be good. Do all your testing to the plug itself to save repeated plugging/unplugging at the cluster.
 
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