Headlight switch issue

Do you have daytime running lights, fog lights, and trailer tow package? Sometimes the head lamp switches are different depending on optional equipment.

Put the switch in the head lamp position, then check for twelve volts on the tan/black wire. If it is missing, fuse 17, a 20-amp, in the under-hood fuse box is blown.

Check for twelve volts on the black/yellow wire. If you have that, the radio's back lighting should be lit up. That wire feeds fuses 7 and 23, both 10-amp, in the inside fuse box. Check for twelve volts on both sides of those fuses.

Sounds like a bad switch. The interior contacts have failed and only connect in positions that are not correct for the detents in the switch. Same type of failure the sliding ignition switch contacts have. If you get them in just the right spot all is good, anywhere else gets you nothing.

It does sound like a bad switch, but it has been replaced already. Do not worry about that "sweet spot". What I want to see is what voltages you find on those wires when the switch is solidly in the "head light" position. If there is no twelve volts on the black/yellow wire, but there is on the tan/black, the switch is bad or wrong.

There is one other possibility. Often the high-current contacts in a head light switch or ignition switch become overheated and arced, and that heat migrates out to two connector terminals. Once the switch is replaced, those two blackened terminals must be cut out of the melted connector body and replaced individually. Failure to replace both the switch and the terminals at the same time will result in the overheated part doing the same thing, and the resulting heat build-up will damage the new part. Overheated and arced terminals that are not replaced will cause no or intermittent operation of their circuit.

Dandy. If you have 0 volts on the tan/black wire, fuse 17, a 20-amp in the under-hood fuse box is blown or that wire has a break in it. I suspect when you slowly pull the switch part-way out, one of the other contacts is making momentary connection so the tail lights turn on. While that is a valid clue in that it proves that circuit works and does not have a short in it, it is not normal operation.

Dandy, I see you said the fuses are good. Did you check for voltage on both sides of the fuse? It may be a voltage supply issue to the fuse.

Roy

You completely missed my comment about that "sweet spot". That is not normal operation and is not a valid test. It only shows the rear bulbs and wiring to them are okay.

The only way to do diagnostics in the circuit is to switch it to the position that does not work as designed, then analyze the voltage readings. You found no voltage on the tan/black wire that feeds the tail light circuit, so of course that circuit will be out. Pulling the switch half way out is connecting the tail light circuit to the wrong feed circuit. That is a function of the location of the contacts within the switch.

You need to find out why 12 volts is missing on the tan / black wire. You said the fuse is good. That leaves a break in the wire between that fuse and the switch, or, as ASEMASTER6371 said, 12 volts is missing to that fuse.

You said, "This concern of mine is hard to explain. My lights they all work, I am getting proper voltage, my fuses are good, ... ", but earlier you said you had 0 volts on both the tan/black and the black/yellow wires. Both of those statements cannot be right. You do not have proper voltage, and the lights do not work properly. Measure the voltage on both sides of fuse 17 and tell me what you find.

Dandy. I don't know what voltage drop you're referring to, but you have voltage at the fuse and not at the other end of the wire at the switch. The tan / black wire is cut or there's a broken connection inside the fuse box where the tan / black wire is attached.

Going back over sold checks, if you have power on both sides of the fuse, the next stop for voltage is the lights. This enforces all our replies about a broken wire between the fuse block and the light. The fuse is after the switch. The fuse only gets power when the switch is in the headlight position. Attached is a diagram.

You're on the wrong diagram. Look at the "Exterior Lights" diagram, then you'll see a different part of the head light switch that is fed from fuse 17, then on the tan / black wire to the switch. I was confused by this diagram too.

Unfortunately we don't know if the previous problem has been solved or what the solution was. If you figure this out or need more help, please post a follow-up reply.

Rats. This is why voltage readings are more accurate than ohm meter readings. My guess is the mechanic knew some diagnostics had been done already, so he failed to check the fuses first. Now the question is why did the fuse blow in the first place?

Regardless, happy to hear it has been solved.