Troubleshooting Loss Of Left Turn Signal With Roadmaster Diode Wiring Kit # RM-154  

Question:

Expert Reply:

If only the left turn signal isn't working on the towed vehicle and is working on the motorhome then you most likely have a loose or damaged wire running to the left tail light, the diodes are bad, or the # RM-154 wiring was installed incorrectly. You essentially have two power sources and the diode just acts as a sort of transfer switch to allow the motorhome to power the lights when connected or the vehicle to power the light when not connected.

If the vehicle has separate lighting there should've been a tail light converter # 118158 and extra diode # RM-790 for each turn signal spliced into the RM-154 wiring to allow you to keep the turn and brake signals on separate lights. To find the break in power you'll want to turn on the left turn signal in your motorhome and then test the 7-way with a circuit tester # PTW2993 to make sure the signal is reaching the 7-way. From there you can plug in the cord and test the 6-pole side of the cord to rule it out as the cause.

From there you can use the hook of the tester to puncture into the casing of the wire for the left turn signal up to the converter and then after the converter. If you're getting the signal before the converter but not after then the converter is bad. From there you'll following the wire over to the diode and test both sides like you did with the converter. They also make it super tight for the spade terminals on the diodes so you might just have a loose connection. I typically press one spade terminal up and the other down slightly to give them a bit more room. You'll want to be careful you don't break off the male spade terminal on the diode though so "slightly" is the keyword here.

While you back at the tail light/diodes it would also be a good time to check that the installer spliced into the correct factory wire for the left turn signal as well.

expert reply by: Kevin C

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