This is my first post so bear with me.

I have a 1979 f-250. It had belonged to my great Uncle and it was incredibly dusty from being on his farm. So I decided to take the instrument cluster apart to clean it etc. The dash lights worked before this endeavor. Now they don't.

At the same time, I was also installing an after-market radio and temperature guage. I had mistakenly taken the two wires to the old radio and assumed one was the ground. After reading a good post on here about dash lights, realized it had two power wires and one was for illumunation of the radio when the lights are on. I have fixed that by capping off that wire.

With a multi-meter this is what I have discovered. I have power to the light switch ( I actually tried a new headlight switch and it didn't fix the problem). I have power to the High beam bulb and left/right turn signal in the dash. I have power to the "fasten seat belt" bulb. The cluster I have has gauges. The plug in is solid and not one of those "turn to dust" cluster backs. The dash lights should be the light blue/red wire I believe. It is #10 on the plastic connector. It has power at the switch but not at the plug in to the cluster.

So wouldn't that only leave a faulty wire between the two? I find that hard to believe because it was working before I started this and is wrapped in a loom. FYI- I also took the ground off and cleaned/reattached it.

I am stumped. Everything works except the dash lights. I also checked the fuse and replaced it just in case. Power comes out of it.

Am I forgetting something simple??? Thanks for any help. It is much appreciated.

 

Check the dash light fuse. Power to the dash lights goes OUT of the headlight switch, to the fuse, THEN to the connector on the cluster. It is indeed confusing because they use the same color BEFORE and AFTER the fuse.

A blown fuse would explain what you are seeing (power going in to the BLUE/RED circuit but not coming out). If you accidently used this circuit as your ground when wiring up an aftermarket head unit, then I would fully expect the fuse to blow.

 

You were correct. I have no power at the fuse. I thought I did have yesterday but apparantly not. I should have power on one end of the fuse block right? All the other fuses have power. I changed the fuse in the instrument light one anyway. If I am not getting power to the fuse where do I check "downstream"?
Also how do I have turn signal indicators? Are they on a different fuse? The high beam indicator power is coming from the dimmer switch right?

 

Do you have power on EITHER side of the fuse? We are talking about the 3-amp instrument panel fuse, correct? Also make sure that you can see power on something that you know should have power, like either side of the brake/stop lamp and emergency flasher fuse. This will prove out your test light (or meter) and its ground. Be careful not to short anything.

The turn signal and high-beam indicators are a different circuit and the dash light circuit has no effect on them.

 

I don't have power on either side of the fuse. I have checked the multi-meter and have a good ground.
So is the headlight switch BEFORE the fuse in the flow? I have power on that wire at the switch.

I'm at work and won't be able to check anything until around 5pm today. Thanks for the help.

 

Hot-at-all-times power goes to the headlight switch (thick YELLOW wire). Unfused dash illumination comes out of the headlight switch (BLUE with RED stripe). This signal is OFF if the headlight switch is pushed all the way in. If the headlight switch is pulled out to either stop, then the signal is proportional to the rotation of the headlight switch **** (OFF if turned all the way clockwise, full 12 volts if turned all the way counter-clockwise).

This wire goes to one side of the dash illumination fuse (3 A) in the fuse panel. The other side of the fuse stays BLUE with a RED stripe and feeds all of the dash illumination (instrument cluster, heater controls, radio dial, headlight/wiper label).

If I read your post correctly, you're saying that you DO have power out of the BLUE with RED stripe wire of the headlight switch, but power does not show up on either side of the fuse. If you're confident in the measurement, then the only explanation for this is a cut wire in between the headlight switch and the fuse panel.

 

I will check when I get home. Something I just thought of is, would I have to have the headlight switch in the "on" position to have juice at the fuse? I'm thinking the answer is yes and I believe that's how I checked it but it was getting dark and my kids were ready to go trick or treating. I will check when I get home.

 

This was explained in my previous post:

 

It is the little tiny glass fuse that is blown. I did the EXACT same thing as you!! I thought one of the wire in the harness was ground because when I tried it with the test light it made the light turn on. Found out the long frustrating hard way!

 

I checked tonight and had power at the bottom of the fuse. then checked the top and had power. Then at the instrument cluster. I hooked it up and the lights worked.

I think this is what happened: I had that hot wire for radio illumination attached wrong which blew the fuse. Since I had also taken the dash apart and the original light switch was in it, figured i broke it/too much dust in it. so i got a new switch. That didn't work. I put a new fuse in and swore I had no voltage on either side of the fuse block last night. I must not have fully installed the fuse and when I touched it tonight it went all the way in securely which completed the circuit and "fixed" the problem.

Thanks for all the help! it was really driving me nuts trying to figure it out.

 

Is the instrument cluster back the original that was made from a composition material that can TURN TO DUST before your very eyes!?

Or is it the hard plastic cluster back that FoMoCo came out with in 1981 to replace the original POS composition cluster backs?

 

Glad to hear you got it worked out.