My dash /instrument guage lights are out and I cannot determine if it the fuse or circuit board. The drivers manual references a 4 AMP fuse for the instrument panel but I cannot find the 4AMP fuse on my fuse panel as most of the markings are worn off. Any advise on how to resolve? Also, once I get the instrument lights working again - I am considering replacing the fuel guage with the OEM 4 guage set up with temp, oil, fuel, etc. Straightforward to replace the fuel guage or more complicated than I am assuming?

The 4A inst panel fuse on the '68 is the short one on the bottom left side of the panel.

If a new fuse doesn't fix , try checking the dimming rheostat in the light switch.

How does one do that? I have the same problem.

Re: The 2nd part of your question - a Rally Guage cluster installation. Suggest you look at the wiring issues involved in the FAQ's on this site. All the details are there.

If your dimmer dims the dome/courtesy lights it's probably OK. Take the switch out and put a meter on the power-in connection and the power-out to the instrument lights and see if there is continuity. Then check the ohms of resistance when the switch is rotated. The meter should show high resistance when at low setting and low resistance when on full light setting.

Thanks for the advice guys. I will first start with fuse, then investigate the dimming rheostat. Should the fuse not be the problem and teh dimmer be working am I then dealing with a bad circuit board or other electrical connection issue?

It's also extremely common to simply have a bad connection due to surface corrosion between the light bulb sockets and the circuit board. Remove the bulb retainers from the back of the circuit board, shine up the connection points with a bit of emery cloth, confirm the bulbs are good and glow on the workbench, and reinstall.

Alternately a missing or broken circuit panel ground wire will fully interrupt the circuit and any possibility of lighting. This is another very common reason for failure.

A test light or multimeter are your friends for this sort of thing. Confirm 12-ish V at every step of the way (while lights are on...with dimmer set full bright), and wherever the 12V disappears is exactly where your problem is. Much faster and less frustrating to troubleshoot like this, than it is to go the trial-and-error of each part method.

You will need different style of sending units on the engine for temp and oil pressure, if you switch from your current dummy lights to gauges. Dummy lights operate on sending unit on/off switches, and gauges operate on sending unit rheostats. Not difficult, just additional parts to replace so the gauges work. And the replacement gauges are integrated with the circuit board I'm quite certain...so if you're fixing lights on a circuit board you're not even going to be using, due to a future gauge swap, you might be spinning your wheels on this lighting project a little bit. So I say swap your gauges first if that is your intention. THEN worry about getting your lights working.

In lieu of emory cloth you can also use a pencil eraser. Not quite as abrasive so it takes a little longer but is a little easier to control. Ditto on the multimeter. You can get one at Harbor Freight for less than 5 dollars and it will do everything you will need. Also get a bag of alligator jumpers from Radioshack. This will allow you to bypass sections of circuity to pinpoint the issue. Lastly, you might want to consider getting some electrical contact cleaner

I changed out the fuses and the lighting in my speedometer and fuel guage still does not work. I checked the light dimmer knob -and the dimmer does not dim or brighten the interior lights. I am assuming at this point that I have either burnt out bulbs or a bad circuit board - but prefer to determine if this is the case prior to removing guage covers, etc. Any suggestions on how to debug further without pulling dash apart? Thanks again.