I'm riding one of those tremendous GL 1500 SE.
After having winterized my bike, I'm currently taking care of it, replacing breaking pads, breaking 'tubes', renovating air filter for compressor, and adding a trailer hook.
This trailer hook is also coming with a 7 contacts trailer plug. On such plug, it is expected to get a single ground cable for all signals : breaks, position, and turn.
But remember, there is this famous way of annulation turn signal, pushing the turn ground up to the battery plus, which means there is no direct common ground

The only thing I've found on the web is an isolator, which seems to fit the need.
I'm having in mind to put 2 isolating relays to get a +12 'flashing' signal, that can be used with the real common ground, then in this famous 7 contacts plug.
I already have such relays, also some 'honda' plugs with some wiring cables, nothing to buy, only time to set it.
Any comments or advices ?
For sure I will add some comments about going from theory to real world

Have good rides for those who can during this winter time
