How to Determine If My RV Has Separate or Combined Lighting for Installation of Roadmaster Diodes

Question:

Could you clarify use of the 4 diode system on a TOAD with separate tail, turn, and brake light assemblies? Specifically with only 4 diodes, you can only splice into TOAD tail light and brake light wiring. You are suggesting in your explanation that the brake light also acts as a turn signal only one of the two filaments in that bulb when hooked to the towing motorhome. How can you determine via the motorhome wiring plug that this is indeed the case??

asked by: Andy H

Expert Reply:

I do believe you're asking how to determine whether or not your RV has a combined or separate lighting system. If the motorhome’s trailer plug energizes the same pins on the 4 way connector for both brake lights and turn signals, then a 3-to-2 converter is already installed and the motorhome should be treated as combined lighting when installing the Roadmaster # RM-154.

expert reply by: Erik B