[ricm]

If you are using MFU as power source it is a bit risky since the extra current drain can pop the MFU. I've known people run a second trailer light set in parallel from the MFU for a road train without trouble (initially, at least).....I've also known people break the MFU trying to add extra head lights which is kinda the same thing. But for 3 lights sets, safest option is to splice opto-couplers into your first trailer light set (one opto-coupler for each indicator, and a 3rd for the tail/ brake lamps). You can use the outputs to drive the mutiple trailer light sets in your subsequent trailers. The opto-coupler isolates the MFU from the extra current draw for the additional LEDs. If you search '4N25' or 'opto-coupler' on this forum you should find a few threads on how to do this. Not expensive to do, but you'll need a soldering iron, a bit of veroboard or stripboard, and a power supply on the trailer where you have the opto-couplers (which you could take from the truck itself).