Hello! I have a 1986 Ford F350, 4x4 crewcab longbed. The truck was originally single-rear wheel, but I have since converted it to a dually.

the dually fenders have two lights on them, each using a positive and negative connection, the 194 lights.

Where can I splice into the original marker light wire on my taillight harness? What does the original dually bed light harness do? Is there a better way to do it other than clipping into the OEM harness?

The marker lights go into the bed plug as one wire, and come out as two for either tailight, so if I splice into this and add two more onto this single wire, making 4 wires off of one, will I see dim lights, possibly melting the single wire?

Thank you

 

Idk how they did it for the 86-down trucks, but the 87-ups use a dedicated relay that powers the dually fenders markers, the ICC lights under the tailgate (duallies need them by law cause of their width), and the running lights pin in the trailer connector. The relay is triggered by the normal running lights, and it's wiring leading to the back of the truck is built into the chassis harness (I spliced a factory ICC blink switch off a Louisville Ford tractor unit in my factory wiring so I can flash my dually-specific lights without interrupting the main tail lights). The bed harness for dually trucks is different from that of the SRW trucks, it has extra connectors hanging out it - one per side at the extreme ends below the tail lights for the fender markers to plug into, and one in the middle for the three center ICC lights. These factory connectors all have 2 wires, brown is power and black is ground. All the grounds are spliced together by the way prettymuch in the middle across the bed, so the chassis harness has only one ground wire for all of the bed lights.

Not quite sure what you mean by running 1 wire and splitting it into 4 tho, but if everything is in parallel then if you make the 1 wire big enough to handle the combined load of your four lights then that's fine, for four 194s your standard 14-awg wire is more than sufficient, could probably go even smaller actually.

 

Thank you very much! Couldn't have answered my question any better. What I mean by "one wire into four," is that there is one power wire coming from the cab, that goes into the bed plug. That plug splits it into two, and goes to each taillight. So if I spliced a wire on to each of those output wires, that single wire coming into the plug would have 4 outlets in total. I just wanted to figure out if this was okay, seeing as how they're the normal bed taillights and then I'm adding on 4 - 194s to that circuit

 

Here's a picture of the dually rear lighting in 1986. They did use a relay from the factory. You are supposed to have the side marker lights AND have the 3 center lights in the rear middle also. I suppose the factory figured this added load needed a relay and different circuit, but people use the original marker light circuit for trailer lighting, so I am thinking it would work without a relay. The wire you are looking for is brown.

 

Relays are nice but in the age of LEDs not 100% needed anymore. Both Grote and TruckLite make nice marker lights that can be had as direct replacement for the factory lights only in LED form, grab some of those and wire them up off the tail lights and you'll be fine cause they draw next to nothing. However be prepared to be blinded by your own markers when driving at night - if you have your mirrors where you can see your dually fenders you'll also see a huge amber glow and not much past it, happens with regular 194s too, not just the LEDs - it's just the position of the lights is too high up on the fenders, if you look at GM and Dodge they both put theirs much lower on the fenders