This is a quick overview of how to connect the BlueTooth trailer module
What I did on mine was on the transmitter board I linked the +5v to all the + inputs on 1-6 then just used the negative lead of the leds in the truck to the plugs.
On the reciever I have again ignored the +ves and used the +5 or battery input. You will need resistors for the leds. Below are the connections.
BB Tail lamp transmitting and receiving board description
0 Power supply 5V
1-6 Marker lights, license plate lamp, left turn lamp, right turn lamp, brake lamp, reverse lamp
The light control is Bluetooth transmission. Pay attention to the signal interference. If the red lights of the transmitter and the receiver are flashing, it means that the signal is lost without matching. Each socket at the transmitting end is divided into positive and negative poles, which are connected to the light wire corresponding to the headlamp group.
This picture shows how I modified and installed mine. I did it this way to make it portable between trucks. I used a 10 way plug to attach it to my Beier unit but any plug system is fine.
The unit has individual opto isolated inputs for all the lights these need a + and a - to operate. If you use a system that supplies battery voltage then you need a suitable resistor in the + line 1k Seems fine but you may have to adjust until the red indicator i=on the transmitter board comes on.
I linked 5 volts from the transmitter board input to all the +ve inputs for the lights, then I dont need any resistors, just the -ve switched inputs ( Beier and servonaut are similar in this respect and this will work with both.
The receiver needs a 5 volt supply, if you have a receiver in the trailer then you can use that to supply it from a spare channel or the battery slot. If not use a cheap 5 volt BEC/UBEC unit.
The outputs are via "open collector" transistors so the supply to the lights can be anything reasonable, i.e. direct from a motor battery up to 12 volts. You will need appropriate resistors for the leds you are using.
NB this unit will only drive around two leds. so standard rear lights are ok. We are hoping for an improved unit shortly.