I'm having trouble with the tow electrics which I installed on my 2009 Mk4 Ford Mondeo Estate. I got Ford dedicated wiring (part nos. 1740024 and 1755427) and installed everything exactly as instructed. I haven't gone to have anything reprogrammed yet, but I was under the impression that the basic functions such as indicators and brake lights should work regardless, and when I plugged a light bar in, nothing lights up, even with the ignition on.

I do have 12V at the tow socket between pins 9 and 13, and I've checked all the fuses. With the brake depressed, I'm only getting about 4V between pins 3 and 6, and similarly, with the hazards on, only get about 4V peak between 3 and 4 for example. I've also checked the continuity of the lights on my trailer board, and they seem fine.

Any advice based upon this information would be appreciated. You may just tell me to get and get it reprogrammed, but I don't want to waste time and money doing that if there's a deeper issue which needs fixing first.

Vehicle has to be programmed to know that it now has the trailer module installed.

Use FORScan and a good ELM327(modified) lead to connect up to the OBDII port and activate.

FORScan: https://forscan.org/download.html

ELM327(modified): https://tunnelrat-electronics.fwscart.com/USB_Modified_with_switch_ELM327/p4541936_17045457.aspx