Wiring toad lights: RT works, LT does not
I've nearly finished setting up towing my 1987 Suzuki Samurai behind my 2001 Safari Trek. Wiring up the lights should be simple, but I'm frustrated by a mystery. The Trek has a six-conductor socket with four wires going to it. I've installed the same on the Samurai, using a diode kit from Blue Ox. I've wired the diodes into the loom in the engine compartment at the firewall. The connections are Left Turn, Right Turn, Tail Lights and Ground. TL and RT work. LT is wired up identical, but does not work! I've swapped parts to verify that the electrical connections are right, the diode is okay, the light bulbs are okay. My multimeter cannot tell me the voltage while the light is blinking, but this Fluke multimeter has a graphic that goes up and down a certain amount when connected. When I check the circuit at the Trek, at the Samurai, at the diode (when the output of the diode is NOT connected), the graphic goes up to the max, just as it does in the RT circuit. But, when I plug in the output to the diode, which goes to the LT lights, the level is pulled down and the light doesn't come on. In the RT circuit, the level stays up to the max as it blinks. Something is holding the LT level down, so the light doesn't blink. But, when I signal LT from in the Samurai, it works normally.
What could be causing the LT to fail on the Samurai?