How to Isolate Stop Light Signal for 3rd Brake Light on 2017 Ford Fusion

Question:

I have a 2017 fusion with a 2 wire system, flat towed by an RV with a 2 wire system combined incandescent brake/stop and separate incandescent tail lights. I have wired the fusion with four diodes and a brake relay since it also has an alternate braking system. The turn/brake/tail wiring is essentially what you have in your TR118821 product with power coming only from the RV lighting system. The problem is that I cannot get the 3rd brake light to work. I have also installed the Curt 56196, 2 to 3 wire adapter, and hooked the brake wire output from that no connection to C56196 turn/brake outputs to the 3rd brake light and I still get right turn signals on the 3rd light when brakes are applied. 3rd brake light works fine with Left turn signal and brakes. Any suggestions on getting the 3rd brake light functioning correctly? Its as if the Curt 56196 is having no effect - I have verified that Curt brake output is correct.

asked by: Jamie

Expert Reply:

Thank you for all of the information about the wiring you are using for flat towing your 2017 Ford Fusion. If you are using the Curt 2-To-3-Wire Tail Light Converter # C56196 in conjunction with a wiring kit like the Tow Ready # TR118821 it should work properly to isolate the 3rd brake light signal but you need to make sure that you are connecting the right and left turn wires to something on the output side. A common misconception is that you can just cap those wires off but when I've reached out to Curt they say that those wires have to be connected elsewhere for the converter to operate correctly.

You typically don't need to have the 3rd brake light activated for flat towing but if you are wanting to wire it up anyways (or for some reason your highway laws require it) you might be interested in the Pacer Performance 3rd Brake Light Logic Module # PP20-702 instead. This simply connects to the stop/turn signals and then isolates the stop signal for a 3rd brake light. This part is commonly used for the 3rd brake light on a truck topper.

expert reply by: Jon G