Another No Rear Lights Thread (Noob Help on How to Test)

[RangerJoey]

Hello,
I'm still in the never ending process of trying to rebuild a '99 XLT Ranger and had the bed off for a considerable time. After putting it back on and being careful during reassembly, I popped in the tail lights and immediately found nothing in the rear worked. At least on the bed. The cabin 3rd brake light does work.

I did a lot of searches on the forum and they were super helpful! First, I didn't even realize the turn signals - outside or on the instrument illumination - weren't working. So I took apart the steering column thinking it was the multifunction switch. May have been. I mean, I ordered a new one but when I took the housing off, I immediately noticed one wire had fallen out of the harness. One of the little plastic "springs" that keeps pressure on the factory wiring was worn away. So I wound up buying a replacement harness and swapping the wires that came with it for the factory wires. Genius! But still nothing.
I checked all fuses both physically looking at them and for continuity using a multimeter. The "Hazard Relay" seemed like it kept coming up in my search results so I swapped that for a new one. Success! Now the dash illuminates when the turn signals are on as well as the hazards. Only problem: They only work in the front.

I found this thread from just over a year ago that really seems like the symptoms I'm experiencing on the 99. I wanted to follow some of the advice given, but how do I go about testing this stuff with a multimeter? I searched a couple of videos and I think I would need a helper and a wiring diagram. And when looking for a ground, it's always mentioned to use a piece of bare metal on the frame. Stupid question: Does it have to be on the truck? I have a couple of layers of POR-15 everywhere on the rear and a good layer of Fluid Film to boot. There's really no bare metal in the rear.

In summary:
-No brake lights on bed when pedal is pressed
-Yes third brake light when brake pedal is pressed
-No rear turn signals
-Yes front turn signals
-No reverse lights
-No rear running lights
-Yes headlights
-Hazards work in front, not in rear
-Replaced Multifunction Switch
-Replaced Hazard Relay
-Verified Fuses
-Can physically see wiring harness to the rear is plugged in
-Has 7 Pin Tow Harness, All Factory Wiring

Could anyone please point me in the right direction on how to diagnose this with a multimeter, (speaking to me like an idiot)?

 

[2011Supercab]

Got to ask,
When you took the bed off, did you unplug the wiring harness at the left rear corner ?

When you put the bed back on, did you plug it back in?

 

[RangerJoey]

OMG - are you staring at the truck right now!?!?!

Okay, so I originally triple-checked that harness that runs over the frame on the topside of the spare tire. It sort of splits. Maybe like a "Y". The part that's super visible (I have the tailgate currently removed), and runs towards the center of the bumper is totally secure. The only other wire/connector I saw was that four plug thing on the tow lights. I cleaned it with electrical cleaner and compressed air but no luck. After seeing your post, I went back to the truck today and saw below. I thought this was the wire running to the license plate. Where could this go (rear driver's side of bed)?

 

[2011Supercab]

Yeah, that plug.

Other end should be inside left rear frame rail.

 

[Curious Hound]

Yeah. Get that plugged in.

and…. Make sure the ground wire for that harness is securely connected to clean bare metal. Yes. Make a clean spot if necessary. Alcohol, brake cleaner, sandpaper, whatever it takes. That usually connects on the rear frame crossmember, right in front of the bumper. After getting a hood tight, clean connection and testing it, then you can put por15, fluidfilm, etc over top of the connection.

 

[Uncle Gump]

D'oh!

You aren't the first and certainly won't be the last