It sounds like you have two different problems, and both are related to the LED bulbs. First of all, whenever you have bulbs doing the wrong functions, it is usually due to a broken ground wire. The glaring and common clue is current can't get to ground so it looks for an alternate path, and that is through a different filament, which can be on the other side of the truck, and through the signal bulb. The signal bulb is sharing the 12 volts with other bulbs, so it will be much less than full brightness.
The second thing has to do with LED bulbs not drawing enough current. With the older thermal / mechanical flashers, too little current causes the flasher element to not get hot enough to flash so, depending on the flasher style, the signal either stays on or stays off, or it might just flash very slowly.
If you have the newer electronic flasher, too little current flow, (as in a burned out bulb), causes them to flash too fast. Since LED bulbs also draw too little current, the flasher acts the same way. The fix for that is to add a resistor to each bulb. I haven't looked into that yet, but a typical 1157 signal bulb has about 12 ohms of resistance. I would guess a 15 to 20 ohm resistor, coupled with an LED bulb, would draw the right amount of current to make the flasher work properly.
I would plug one of the original headlight assemblies back in and verify that side works properly. If there is still a problem, look for a wire in the truck's harness that was brittle and broke when you flexed it. If the lights work properly, the next suspect is your new light is wired incorrectly. That isn't something that can be easily examined or described over a computer.
You can also buy an electronic flasher made for LED bulbs. I bought a few of those, also on eBay, for less than four bucks, and they work fine. If everything else is wired correctly, plugging in one of those flashers is a lot easier than soldering in a bunch of resistors. Those are meant to replace the older thermal flashers.
Friday, February 6th, 2015 AT 8:45 PM