Bypass Relay ECU for towbar wiring. Maypole brand. Free post
Necessary for modern cars to protect vehicle computer. Bypasses the car lighting system for power but senses which circuit is being used eg brake, indicators. Bought one locally that I needed in a hurry to tow a boat I bought ($140). Had this on order but it arrived a few days too late. Now not required. Simple to install. If ad visible then still for sale