Almost nothing works on my 68. Where to start?

[cghstrojan08]

Just picked up a 68 F100. When it comes to electrical, the only thing that works is the ignition and when you hit the left turn signal it comes on in the dash solid. Other than that, nothing else works. Where should I start at? I was going to look at the fuse panel this week. The only gauge that works is oil pressure. Just seems weird that almost everything doesn't work.

Also, this doesn't have a fuse under the hood. That horn? Its just below the battery on the passenger fender.



Also, here is a pic of the ol gal.

[67mann]

no electrical wizard, but I would start by checking the grounding of the system and lights(bulbs)after seeing if the main fuse and all others are good....

[68RGR]

Yes, check the fuses. If any are blown, that will give you a place to start.

Make sure there is power coming to the fuse box. Look for unconnected wires under the hood.
If you find any, use the wiring diagrams on this site to ID them based on the wire colors.

I think I would pull the instrument cluster to check for burned, damaged or butchered wiring.

A miswired trailer connector can create all sorts of lighting issues.

A failing ignition switch could create the issues you have - Does it feel loose, like its worn out? If so, it can cause big problems if it decides to literally come apart like mine did.

The turn signal issue could be the flasher but that doesn't explain why the other side doesn't act the same.

A 12 volt test light can be very useful for tracing electrical problems.

[cghstrojan08]

Ya, I figure a weekend of me and the test light will hopefully figure things out. Just sucks I have to get a new one since the last time I used it on a friend's vehicle it got destroyed.

[cghstrojan08]

Well got the time to look at it. I got the headlights and tail lights working. Needs a new headlight switch and the floor button for the brights. Brake lights work and I can make the reverse lights work but the sensor is ripped out. There are some wires though behind the instrument panel that are not hooked to anything. I took some pictures and will upload them later. One of them is a orange wire that goes up the door pillar from behind the gauges. Another thing is the center fuse which is the little one has no power on either side with the ignition on.

[Calfdemon]

There will be 2 wires that go up the door pillar above the door. Once will be the cab light, and the other will be the fuel tank sending wire for the tank behind the seat. Off the top of my head, the fuel sending wire is orange... I believe the cab light is blue? But that is what you are dealing with right there anyway...

[cghstrojan08]

Maybe that is why my fuel gauge doesn't work. I tried grounding the wire at the sending unit and got nothing.

[cghstrojan08]

Here is the orange wire.

IMG_20140408_125513_366.jpg

Here is like a black wire that with nothing on the end of it and some 3 prong plug that is missing a wire.

IMG_20140408_125621_219.jpg

[Calfdemon]

The 3 prong plug is your ignition plug for accessories. One plug goes to your windshield wipers, as that is how they wired it stock from the factory. Don't remember what the 2nd plug might go to. They always came with 1 or 2 empty from the factory so you can use it to hook up accessories. That 3 prong is hot when the ignition is on.

I installed 4 relays under my dash and use the 3rd socket As the signal to turn my relays on. I use the 4 relays to power my accessories which include my stereo, 2 extra cig lighters / power sockets, and my aftermarket gauges.

[Calfdemon]

As for the orange fuel sending wire, it should have a socket type of connector on the other end of that wire which just snaps on to the top of the sending unit. As for the bullet end you have pictured, there should be a female connector there somewhere that the bullet plugs into. The female end will ultimately lead to the dash harness plug which then will line up to the fuel gauge wire. I am going completely off of memory here so I could not tell you the color code but you should be able to find it here on the wiring diagrams on the site.

The reason that they ended the wire with a bullet instead of connecting it straight through was because the trucks could have been ordered with 2 tanks and they had a tank gauge selector switch under the dash to switch between the sending signals. So the wiring off the dash harness plug ends in a female connector. On a single tank setup, that orange wire plugged directly into the female. On a dual tank setup, there are 2 orange sending wires which go to the selector switch. The switch then hooks up to the female plug so whichever setting the switch is set at (right or left) determines which signal goes to the gauge.

[68RGR]

The smallest fuse in the box is for the dash lights. An AGA-2 fuse.

It should have power when the headlight switch is on. If the fuse is good, the dash lights should work unless there is another issue or maybe because the headlight switch is bad as you said. Don't forget to rotate the switch knob!

If the fuse is blown or blows when replaced, check the cig lighter. In the factory version, there's a light that illuminates the LIGHTER marking. My socket had been replaced with a generic one and was miswired. The PO had connected the wire for the light to the GROUND terminal on the new socket. Fuses blew rather rapidly. I soldered a wire to each end of the blown fuse, put it in the fuse box and connected a bulb across the fuse. Turned the lights on and started looking. When I disconnected the wire from the lighter socket, the bulb went out. Problem solved.

I'm thinking the switch should be replaced first. But, you COULD just power up the fuse terminal to see if the dash lights are working. Those AGA-2 fuses can be hard to find.

Good luck.

[cghstrojan08]

I think the whole reason why the headlights were not working before was because the floor switch for the brights was messed up. You either had brights or nothing. I noticed that the coil looking deal on my headlight switch was hanging down. When I get off work in 3 hours, I have a new headlight switch to put in. Hopefully get the dash lights working. I tried looking at the wiring diagrams but seem to get lost. There is also a fuse under the hood coming from the box on the firewall next to the battery. Sorry, I am tired and drawing a blank on what it is called. **Voltage regulator.

[68RGR]

That coil is the rheostat that dims the dash lights. If it is defective, no voltage to the AGA-2 fuse and no dash lights.

If your truck has gauges, I seem to recall that there are two 4 amp fuses shown in the wiring for the ammeter. I saw the photo - Look for a second fuse holder. If there is a 4 amp fuse in either one, I'm thinking they are for the ammeter. One side of the ammeter taps into a splice between the alternator a battery terminal on the solenoid. The other one connects to the battery terminal on the solenoid. The ammeter is actually a voltmeter that is measuring the voltage drop in the wire between the splice and the solenoid. The drop is proportional to the current flowing in that wire and the ammeter is scaled appropriately to indicate the direction and amount of current flowing.

[cghstrojan08]

This morning I got the new headlight switch in and the switch for the brights that goes on the floor. I have hi/lo now and gauge lights. Also found that wire that connects the fuel gauge to the wiring harness. Grounded the fuel gauge wire and the needle went up. Now I need to find a new sending unit since mine is junk and no float on it.

I think the little fuse I have apart under the hood is for the ammeter. Still don't know why the temp gauge doesn't work. Anyway to test the wiring and gauge in the dash like how you can ground the fuel sending unit wire?

[68RGR]

The temp sending unit is, more than likely, a thermistor - A resistor that changes value as the temperature changes.

I would suggest verifying the wiring between the sending unit and the gauge. The sending unit on my truck is screwed into the intake between the distributor and the carb. It has a single wire going to it.

You can check the resistance of the sending unit to ground with the engine cold and compare that to the resistance when the engine is hot. If the unit is working at all, the resistances should be different. If the sending unit is open or doesn't change resistance with temperature, it's bad. But, based on the other issues you've found, it just might be a wiring issue. Verify that it is connected and that there is continuity from the sender to the gauge.