Thread: Finally Buying a D3

For any trailer with LED lights you'll have to run a resistor module. The D3 sends a low voltage pulse down the line to check for blown globes and to know when a trailer is attached, but it's enough to make LED lights flash and the car dosent recognize that a trailer is attached. Your options are either use an inline module between the car plug and trailer plug, or hard wire one into the D3 - but it will need to be able to be bypassed when not towing otherwise the car will constantly think its hooked to a trailer

Have a read of this thread, you can install the resistors in the car but make sure you can switch them as you say you will be towing both kinds of trailers. Also make sure they can safely dissipate the heat that they generate.

http://www.aulro.com/afvb/d3-d4-rrs/...-big-tick.html

Linear electronics is definitely worth your time getting as the solution is quick and easy with no stuffing around:

Linear Electronic Design | Buy Now

EDIT: also, if I remember correctly, the D3 needs more than just the resistors to solve the issue.