Help, No Instrument Cluster Lights - 70 Jimmy

[Resto-Rat]

I have a 1970 Jimmy and cannot get the instrument cluster lights on. I have new dash, all OEM gauges. New circuit board. All of the bulbs are new and test for continuity across the ground circuits and the opposite side of bulbs. Turn signals work, high beam indicator works, brake light works. Oil is manual. Fuel works. Hazard lights work. Light switch brings on lights and high beam changes to high beam. So I am confident the dash and circuits are good.

I have puled down wiring diagrams and the instrument cluster electrical connector uses the light grey wire to the number 8 terminal (second one from the right on top above the blank number 5 slot. No power there.

I have gone back to the fuse panel. The fuse has continuity on both sides so fuse is good. But with a test light no power on either side of the fuse.

According to the wiring diagram, the light grey comes from the dash into the fuse panel, and the other end of the fuse is fed by a dark green wire that comes from the dash light switch.

I have pulled the plug off the switch and get no test light joy on any of the terminals on the plug. The light switch works to turn on the lights.

Any ideas on how to find the problem?

Could it be a bad Light switch? It works for the lights so not sure why it would not work for the cluster lights.

I am assuming that power comes into the light switch from probably the 12R big red wire. But not sure how to test that. When I use a grounded test light no joy touching that plug in the connector?

Could it be that the Green wire feeding the fuse panel if I am correct form the light switch is bad. Should I have continuity between green end of the fuse and the terminal on the switch? Yes?

Since I am not getting power to the inbound side of the fuse (assume the Dark Green) I again don't think it is the light grey wire going to the cluster?

Any other thoughts?

Sammy

[VetteVet]

All your assumptions are correct and you know more than most about the wiring. The green wire for the dash lights is fed by the orange wire to the HL switch which also lights the parking lights. Before it powers the green wire, the power passes through the headlight rheostat which is the dim to bright for the instrument lights.

Simple troubleshooting for the instrument panel lights is to jump power to the green wire side of the PNL lts fuse and see if the lights come on. If they do then the problem is between the fuse and the headlight switch, either an open in the green wire or the HL switch. I would spin the HL knob a few time and see if it wasn't just light corrosion and maybe they would come on.



Good Luck.

I have a diagram of the AC circuit if you think it might help your AC problem.

BTW welcome to the forum.

[Resto-Rat]

After I fretted over this a while I went back to shop and checked continuity from the light grey wire on the panel to fuse and that is okay.

I then checked continuity from the plug to the panel fuse. Oddly enough all of the plug terminal spades test positive for continuity to fuse panel EXCEPT the dark green.

Now you said something that the reostat controls. My knob does not spin at all. That may be the problem. Seems like it may be in the switch. I will do as you suggest and jump power to dark green fuse side and test.

Should all lights have a reostate and spin. Mine may just be bad. I live in La Grange Texas. Small town in Texas with good NAPA. Is that switch a LMC item or do you think NAPA would have one?

Thanks for all your help. And got the ac diagram. Very helpful.

[Resto-Rat]

Napa online says they have one. For $15 I am on my way to see if I can just cut to the chase.

Posted a few pics of my Jimmy. Original Paint

[VetteVet]

Originally Posted by Resto-Rat

Napa online says they have one. For $15 I am on my way to see if I can just cut to the chase.

Posted a few pics of my Jimmy. Original Paint

Beautiful truck you should be very proud.

[VetteVet]

Originally Posted by Resto-Rat

After I fretted over this a while I went back to shop and checked continuity from the light grey wire on the panel to fuse and that is okay.

I then checked continuity from the plug to the panel fuse. Oddly enough all of the plug terminal spades test positive for continuity to fuse panel EXCEPT the dark green. If you mean the light switch plug then you should have continuity to the fuse panel. You might have a problem with the connection on the fuse panel behind the fuse and very rarely the terminal crimp gets the insulation and not the copper wire, which would explain lack of continuity.

Now you said something that the reostat controls. My knob does not spin at all. That may be the problem. Seems like it may be in the switch. I will do as you suggest and jump power to dark green fuse side and test. You may also jump power to the green wire at the light switch plug and the four instrument lights should come on. Make sure that the fuse and the holder is clean and snug.

Should all lights have a reostate and spin. Mine may just be bad. I live in La Grange Texas. Small town in Texas with good NAPA. Is that switch a LMC item or do you think NAPA would have one? There are several suppliers of parts for our trucks and NAPA is one. They also sell off shore stuff just like LMC. I bought a brand new gas tank sender from a place online and I was tickled to death with it if I could just remember their name. They sell most everything for our trucks and the forum venders are very good as well. GMC Pauls has been around here forever.

Thanks for all your help. And got the ac diagram. Very helpful.

I'm glad but I wish I could help more on that issue.

[VetteVet]

PartsGeek.com and they have lots of stuff for our trucks.

[Resto-Rat]

Took all the dash back apart. New light switch. Someone had soldered the reostat in one location and that was a bad location. So no power to Dark Green. $18 dollar switch and all back together all back in business.

Thanks for all the help.

[Mike C]

Nice truck. Congrats on the easy fix. I was going to comment to check the rheostat. Mine went out 30 years ago (LOL) whacking the dash lights but was back in business with a junkyard special.

[VetteVet]

Originally Posted by Resto-Rat

Took all the dash back apart. New light switch. Someone had soldered the reostat in one location and that was a bad location. So no power to Dark Green. $18 dollar switch and all back together all back in business.

Thanks for all the help.