So I have a 1978 Ford Lariat with 67800 miles. I described this in another thread, but my gauge lights we out when I bought it less than a month ago. Then the gauge lights worked for awhile, then went out never to come back on. Many helped people said I need to replace the headlight switch, which I did. No gauge lights after the new switch but every other light- headlights, dome/interior lights, running lights, everything. I didn't check the fuse yet, but besides that, any other ideas? It would be different if the gauge light never worked, but they did for a short time. Any ideas are appreciated.

 

Check the fuse, and if that's good, then you're looking for light blue wires with a red stripe on them. That's typically the instrument illumination circuit. There's definitely at least one wire that color going to the switch, and there should be one going to the gauge cluster.

Sounds like you're looking for a wire which is broken and barely hanging on, or possibly one where the insulation is compromised, allowing it to short - especially if your fuse is blown.
Your radio dial should illuminate, (if factory radio) as well as the HVAC controls, and the indicator for your headlight and wiper switches.

And if you have an aftermarket stereo, an improper installation (wiring) can mess with the gauge lights too.

 

As stated, check the fuse first. These trucks are notorious for ground issues also. I've slowly fixed all my interior lights in my 78, but I've got intermittent ground problems where the turn signals will quit flashing, or the left rear marker light will randomly go out, then come on later... I'm just trying to buy time until I do complete tear down for the motor swap and repaint to do the re-wire.

 

To start, when you say gauge lights I am going to assume you mean the ones that light the cluster, not the warning lights some trucks have for oil & temp.

Do the lights for the heater control & wiper switch illumination work? If they do, your fuse is good. If they don't work, along with the gauge lights not working, the fuse would be a good place to start.

If the fuse is good, & the heater control light works, It could be a couple of things.

The back body of these clusters likes to crumble & fall apart, especially if the truck is from somewhere hot & sunny. When the cluster body starts to crumble, it no longer holds the bulb & holder tight to the PC, thus does not make contact & the light doesn't come on. If you pull the cluster & see the bulb holders are really loose, & the back is crumbling, you have two options. Look for a good used back, or buy a new one made of updated material. Either way you'll have to swap all your cluster parts over to it.

It could also be the bulbs themselves, bulb holders, or the PC. Replace the bulbs with new, clean the contacts on the bulb holders & bend the part out that makes contact with the PC to give it a little more tension. Test the bulbs in the holder before you install them to make sure they work. Clean the area on the PC where the holder makes contact. While you are there you might want to do this with all the bulbs & holders in the cluster.

 

I had a similar issue with my 78 bronco. Dash lights worked, changed the turn signal switch, dash lights quit working. Turns out I pinched a wire for the gear indicator and blew the fuse. Reconfigured and all is well.

Another thing to consider is the connection between the fuse and fuse holder. Many times have I remedied an electrical issue on my bronco simply by poking a fuse.