Truck tail light mayday. 3 wire to 2

Ok, at my job now, older 4700 IH truck with rotted off tailight wiring. It has the separate turn and brake light wires so 3, tail, turn, stop. Plus B.U. and ground of course. So i bought a Hopkins brand converter. it has five into four, In: ground, tail, L turn, stop, R turn. Out:ground, tail, Left/brake, right/brake. the converter is usually used to wire a trailer plug but this truck is using the old standard two bulb tailights (BU and tail/stop). so I wired these in series and also tee'd off to the trailer plug. I have brake going in to the converter but none coming out. Bad converter? any ideas?

Easiest way to fix that is to put the same number of lights on that were there in the first place, really doubt any converter will fix your problem. might have been cheaper to buy the correct number of lights than what the converter cost. Good luck.

Rather than criticize the way you did it, I will try to answer the question that you asked.

First thing - have you connected all 5 wires in? If not, the converter might require a good ground to work right.

Second thing - do you have a good ground? Check for voltage across the stop and ground inputs. If voltage is good, check for voltage out between right/stop and ground or left/stop and ground.

If all inputs check out good and you still have no output, the converter is probably bad.

If you have any instructions that came with the converter, there may be some sort of initialization procedure required.

There cannot be series wiring. I will make a sketch and post it very soon here. Jim I have three vehicles with that system.

like this only the other way around. The truck has five wires from the front:ground, tail, LT, RT, stop into the converter then 4 out to garden variety tail lights. which use four: ground, tail, LT/stop and rt/stop. Just put in another converter to no avail. What am I missing with something so simple? I'm simply converting to four at the tail lights which I was going to have to do for the trailer plug anyways after.

Yes, all five in connected. ground good and shiny, tail good-working, left turn good going in, right good going in, stop good going in. thats five in. four Out- good ground, good tails working, no left turn/brake out, no right turn/brake out. tried two converters. I'm not the first person to put a combo light on a vehicle so what am I missing? Always hits on late friday!

My diagramis for your problem. The 4 wires +backup lights are what is coming to the back. hook them as shown. (the terminals/wires may be in different order, but there. Your new lights, and the trailer plug attach to the 3 wires plus ground shown at the bottom of the illustration. The module must have a ground.

I am puting my tailights after the converter using combo turn/stop style lights that use 4 wires and teeing off to my trailer plug. So I have 5 from truck chassis to converter then 4 out to truck lights and trailer plug. But I have inputs but no output. Now Im finding that the converter is rated for 2.1 amps per bulb and web says typical 1157 is 2.5. so maybe im overloading the converter. There is a 12v powered converter which supplies 4.5v to each bulb that may be what I need. FYI the 5 wires in count the ground, B. U. is a separate wire.

The best solution is LED bulbs. They are not expensive, last 10 times longer, are brifght, and use .15 the electricity. Jim

depending on which type of flasher unit you have, the flashing circuits expect a certain amount of bulbs or they will not flash... You adding the converter in the circuit may or may not make the flashers fail,,, but you can change to a hd loaded flasher that will fix the amount of bulbs or loads and flash irregardless. the turn signals usually use the sensitive flashers where the emergency flashers used the better unit. ymmv..

I should add, since this is a Med duty truck it uses the non cancelling turn signal switch hung on the side of column-factory IH. While Im testing the turn signals in
front and on side of front fender are happily flashing away.

Never used a converter but looks like their several styles, for converting the trucks lights the simple Tekonsha 118158 3 wire system would be my choice, don't see the need to run tail lights thru the converter

No, I dont see the need to run tail lights through the thing either but thats the way its made and Im finding that they are sensitive to all kinds of things.

Ok, so heres what I've found out. I studied the net and went back into work today (shock) to try some things. I should point out, I am not just converting 5 wire to 4 wire for trailer towing. I was trying to convert the truck also. Since someone had at one time removed the 6 back lights ( 2-tails, 2-brakes, 2- B.U.) and added what I call Jeep style with the shared brake and turns. They had used a jumper to make brake lights and caused back feed which resulted in one brake light. So I figured Id put in the converter and keep the lights and go on to my trailer plug. Not so fast. My research led me to a cycle forum which yielded that these converters need lights connected ahead of them. Somehow they use the ground through the opposite brake bulb to flash (dont ask me). My test light was enough ground without even lighting. So, today I mocked in separate turn, brake and tails on the truck like it would have originally and tied into those with my converter. THen I hooked 4 wire lights with common brake/turn to the four wire end of the converter as if a trailer was connected Voila, brake, tails and turns! on truck and "trailer". But!! no brake lights through to trailer! Please note: during all this everything out front is working properly, running lights, turn signals, head lights. GRRRR! so now I am home stewing. The converter is supposed to be plug and play. Several cars have them from factory for towing. This is not new science but is blowing my tired mind.

I should correct: Brake, tails and turns on truck but NO brake lights through to trailer only turns and tails