I have a 1979 Ranchero that runs great has a solid body but is driving me crazy with electric problems. First my gas gauge was working fine then started to float sometimes only rising to E then starts working fine is it the tank or gauge itself.Also my temp gauge does not work hope the circuit board in the dash isn't going. dont really care about temp but I need the gas gauge bad! Last but not least my headlight switch started with original the dash lights went out.Got new switch the tailights wouldn't work. Took that switch out got switch for 80 LTD didn't have opening for courtesy light plug tailights still wouldn't work until I cut the plug off for the courtesy lights then all worked fine but courtesy lights no big deal! then the switch got hung up and the dim spring broke just my luck buy the same 80 LTD switch and the tails don't work again driving with no dash lights driving me electric CRAZY HELP !!!!!
I had a ford fairmont wgn. The gas gauage was going cafooey on it also. The problem was a corroded contact to the chassis at the tank. I also had a 82 ford truck the gauge kept reading full on front tank. The wire was broken at the tank. Again the ground wire. My 78 truck same problem on the front tank.
So I would check the ground wire at the tank of your car.
The headlight switch sound like you got problems in the harness to the back. Can't say for sure where that would be. I always just have to keep checking the harness with a tester till I find no power. Or you are having bad luck with switches being faulty.
Have you removed the instrument cluster and inspected the printed circuit to see if it is damaged or has any melted spots. Even the bulbs where they turn in can cause damage to the circuits.
But I'm sure the gauge problem for the tank is the wires at the tank.
Another source of these gremlins is that big multi-pin ellectrical connector that leads the harness through the firewall. Gets moisture and corrosion in it. It is held together by 1 bolt. Open it up and spray contact cleaner in both sides before reassembling.
Glazier, does your Ranchero have the small voltage regulator for the gauges? If so, maybe it's bad.
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For the gauge problems, I would check the wide plug at the back of your cluster, make sure it is seated and locked. To test the Instr. Volt. Reg./ IVR (SMALL RECTANGULAR SILVER METAL BOX in back of the instr. cluster) Disconnect the wiring conn. from the term. at the fuel sender unit.Clean them and conn. a lead from a 12v. test light to the yellow & black wire or Pos. lead of a volt meter to the yell,&blk. wire. Take the other end of the test lead to a suitable ground, turn the ign. switch to the on position. A flashing light or flucuating voltage will indicate that the IVR is operating. As far as the tailight problem check the plug at the headlight switch, they tend to melt from heat.Also I would check the dimmer switch at the floor board for corrosion and or melting. Good luck, hope this helps.
Just joined this forum. I have had a 78 Ranchero, a 79 Ranchero and presently have a 74 model. The 74 is being worked over. I have just a small amount of work to get the engine complete. Next will attack the body. Good shape except for two or three spots (rust) and them will paint or have painted.
About your 79 electrical problems, I had a temp gauge that would not register properly, and the problem turned out to be the ground connection between the engine and the firewall. This could be your problem with both of your gauges.
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