I see Zener Diode's and resistors, installed on all your switches and relay circuits, in your future...
What do I know?
Search my post for Fly-Back isolation or search the internet.
Most of the links you find on your first page of results, will waste your time. You'll need to deep dive.
3-4 hours of searches, is what will bring you the actual way to isolate fly-back.
Idiots making bad things get censored from the search engines, so I hope you do not pop up on the radar, as one of them...
Everything matters, all the time.
Fly-Back is no joke. Buying the parts, is no joke. Activating an account at an electrical engineering supply company, is no joke.
Your underwear had better be very clean.
That capacitor, required for overloading the electrical system, had better be a quality unit within 4 years of manufacturing, or it will kill your system.
A 1 micro-farad cap is only rated for 2-3 years of use. It is a disposable item and requires excellent ground fault protection.
Installing audio systems into a vehicle is high science. Learn or get screwed by a shop with bad manners.
When you burn up the diode in the cluster, installing a radio with high power amp and cap, you'll create a volatge drain in the cluster which you you cannot repair. It will kill your battery. every day you charge, it will die in three days, untill you replace the damaged cluster.
It's only $350 plus shipping plus a core charge for a repaired cluster from R/A.
I wonder what they put in there?