Well I got a 1967 instrument cluster from a good friend of mine for this weird science test that I do. I will take a picture of the gauge when I get it out, and post it.
I get these random thoughts going thru my processor that might have reassembled the 1968 instrument cluster incorrectly.
Does anyone have a picture of the back of the instrument cluster centering on the fuel gauge? I might have put the resistor thingy in the wrong place.
There's really no way to put it back together wrong. And typically the gage is not defective, but the sender itself. Time to drop the tank and check sender resistance. 0-90 ohms, 90 being full position.
Funny we are going through the same drama at close to the same time with your electrical. Getting the gauges to work and finding a bad fuel gauge. I have Ralley gauges but still the same issues with the Gen and fuel gauge. I have all kinds of pics.
What I ended up doing on mine was pulling out the guage cluster and testing everything with a 9 volt battery, allagator clips and 500 ohm POT. I verified my gages worked, and that I had good grounds. I replaced all the bulbs, the sockets, printed circuit board, bead blasted and painted the inside of the metal housing white and the outside with weld through primer.
Guess what, don't spray the outside with weld through primer it doesn't conduct electricity. In fact it makes a pretty darn good insulator. I ended up scrapping a bunch off in certain places to get my grounds and Hi beam light to work.
I put dielectric grease on the big connector that mates to the printed circuit board and on each of the bulb sockets. Makes it much easier for the bulbs and connector to go on and off without damageing the printed circuit traces.
I traced my fuel gauge problem to the tank. The very thin coil resistor on fuel sending unit had corroded apart. I was able to kinda make it work until I got another one. The big issue now is the gauge would not got all the way to "E" when empty and goes way past "F" when full.
Get back to work on that dimp Gen idiot light issue. I want to see how that turns out:)
From what I have been able to find out is the resistance is 0-90 ohms with 0 = empty and 90 = full.
What I am thinking (which is dangerous) there is a voltage drop in the 12volt supply feeding the lamps and the fuel gauge. This causes the Gen light to come on and cause the brake light to dim. The Gen light is finding a ground thru the brake light ground when it is on I think.
Why I am focused on the Fuel gauge and Sender unit is that it is not easily removed for inspection. I can take the connector off in the trunk to test (no done yet). That leaves the Fuel Gauge; I now have a spare to use to test that theory.
I know I am on the right track I just need a kitchen pass to work the issue.
One quick way to test the fuel sending unit with out droping the tank is to disconnect the connector inside the trunk just below the lock. One wire goes to the licene plate light and the other is the positive line for the fuel sender. If you ground the line going back to the gauge cluster you shold see it go to E. You can also measure resistance to ground through the wire back to the fuel sending unit as well. It might be best to use the actual ground wire that should be screw down to the gas tank bracket behind the gas tank under the car.
You can do both tests and in a few minutes and know weather or not your fuel gauge/fuel sending unit are working.
