Project - Trailer light wiring with amber turn signals

Not open for further replies.

Thread Starter


Joined Jan 19, 2012
Hi, I've got a project that I shelved a couple of years ago, but now I've got the time and energy to bring back to life. If any of you could suggest a circuit design, I would greatly appreciate it!

The only problem is that I haven't designed a semiconductor circuit since high school, so I've got no idea what chips I need to get started. I am still handy with a soldering iron, though!

My car has a 4-pole trailer wiring circuit-- left, right, tail, ground. It's designed so that the left and right turn signals are red. I prefer to have amber turn signals, and red for brakes only, so the goal of my project is to take the 4-pole wiring from the car, and run it through a circuit to get separate outputs for left, right, brake, and tail.

The tail part's easy, so I'm not worrying about the details there. The hard part is getting the left and right to give left, right, and brake as outputs.

I need 12v outputs (<200mA) according to the following logic table:

L=left, R=right, B=brake. i=input, o=output.

Rich (BB code):
   Li Ri => Lo Ro Bo
L. 1  0  => 1  0  0
R. 0  1  => 0  1  0
B. 1  1  => 0  0  1
Naturally, the 12V power supply for this circuit will have to come from the L/R/T inputs.

For the L and R circuits, I think I need an XOR gate to compare the left and right inputs, and then two AND gates to compare the XOR's output with each of the L and R inputs.

For the B circuit, I think I just need an AND gate to make sure both the L and R inputs are on.

Thanks for any help you can provide!


Joined Sep 7, 2009
This is actually very easy to do: I assume you will be adding separate amber turn signals (single filament) and still retain the stock brake/running light (red lense) which uses the dual filament bulb (typically 1157).

The turn signal power comes from the TS switch which has a flasher in series. It selects L/R, just connect these lines from the switch to the turn signal bulbs.

The brake light power comes from the brake light switch, connect to the higher power filaments of the dual bulbs (red). The running light power goes to the smaller power filaments of the red lense lights.

Thread Starter


Joined Jan 19, 2012
Hi Bountyhunter,

Thanks for the quick reply!

My intent with the trailer is actually to implement the lights with a couple of RGB LED strips. I can handle wiring individual L, R, B, and Tail signals into the LED strip, but my problem it how to get LRBT signals out of a 4-pole flat trailer connector, which only gives LRT signals.

I don't want to alter my car's built-in wiring-- I'd like to use the 4-pole flat trailer connector.

While looking up some ICs, it looks like a 4070 chip will be able to separate the L & R signals, then I just need a chip with an AND gate, I think. I have no idea what I need to support such a chip though, when it comes to resistors on inputs, etc...


Joined Mar 24, 2008
The All About Circuits forum Administrative Team has elected not to host discussions of automotive electrical system modifications/enhancements due to safety concerns, the potential of legal ramifications and the possible circumvention of vehicle regulations at the state and federal level.

This thread is against the AAC forum rules, Chapter 6, as seen here:

Automotive modifications of any kind are strictly forbidden. Therefore, this thread will be closed.

Please try to understand the reasons behind this action, and feel free to browse and use the forums.

You might find answers to your questions in one of these forums:
Not open for further replies.