OK, let me share what I know so far. I realize that I am working with a few different circuits here.

Headlights:

• No Hi or Low beams.
• I have power on both sides of Maxi Fuse 11
• I do not have power on either side of fuses 4, 8, and 33
• The corner marker lights on the cab illuminate when the headlight switch is turned to either Park or Head. However the tail markers do not function.
• The front blinkers function but the rear do not.
• I replaced the headlight switch (I already had it laying around) with no change in behavior. Therefore I am assuming the dimmer switch is getting power from the headlight switch but I have not verified this.
• I do not know if the Flash-to-Pass is working. The truck is in a field and I have no one to look at the headlights while I cycle the switch.

My hunch is the Multifunction switch is bad.

Taillights

• Fuses 3, 7, 13, 21, and 22 all have power on both sides.
• The only thing working on the bed of the truck is the license plate light on the step bumper.
• There is no current at the 6 pole trailer connector.
• The third brake light and courtesy light on the cab function correctly. That tells me the brake light switch is working.

I am suspicious that there is a connector between the cab and the bed that is possibly bad, but would that not also include the license plate light? If so, why is it working?I have not yet tested the sockets in the tail light housings.

Any wisdom or knowledge anyone can add would be appreciated.

Thanks!

 

Yes multi-function switch issue would explain some issues, but only head lights

In 1996 the turn lights only have 1 wire out for each side, other years had one wire for front and one for rear, so 4 wires
So its odd that rear turn are not working, when front are, so not a multi-function switch issue
And of course rear brakes not working as well, they don't go thru multi-function switch in 1996 like in other years

There is a common connector for these under left rear of bed, not sure where it terminates in the engine bay

The park lights do have a Relay starting in 1995 IF...... anti-theft and/or Keyless entry was optioned, so Park lights could be Flashed when locking and unlocking vehicle
But license plate light would be on that same relay, Brown wire that runs from relay to ALL park lights
If no keyless entry then Main Light switch turned on Park Lights/brown wire power, so no relay


Diagrams below
Headlights can also have a DRL module, but those didn't usually cause any issues

 

No key-less entry on this one. It seems I'll be spending some time chasing the harness under the bed.

 

Update time...

• Headlamps are now functioning as expected (Hi, Low, Flash to Pass). Maxi-Fuse #4 was bad.
• I have tested the combo switch and it functions as expected.
• Instrument lights and dimmer work as expected.
• Emergency flashers cycle at a normal rate, turn signals flash fast.

Basically everything in the cab is functioning. On to the taillights...

• All light bulbs in left housing test good.
• Testing for either power or ground on all three circuits at the left sockets and at the trailer plug fail.
• If I ground the taillight negative and put power on the positive I do read the correct voltage but the bulb does not light.
• A brief inspection under the bed looked normal.
• As before the license plate light functions normally.

The next step is to pull the bed off. I don't have any other ideas.

 

If you read correct voltage then bulb is bad or the wrong style, so not making connection

 

OK, I feel like an idiot.

I had some time today and started testing at the harness plug under the cab. The cab side of the plug was tested by having my son turn on the different circuits so I could check if the voltage went on and off. That went well. I didn't have a good way to check the other side of the connector so I pulled both taillight housings. Nothing amiss there. Next I climb under the rear of the bed and found at least 3 different trailer connectors zip-tied to the frame. I came across the problem digging around in that rats nest. The harness connector at the center of the tailgate was unplugged. Seriously! :D

Moral of the story... Check all of the connectors before assuming something worse. Ugh!

At least we got a good laugh out of it.

 

Sounds like a learning process !

Good lesson on Headlight.Taillights Circuits.

Good you got it together.