R21EC installing new chart plotter

[Stevo]

Greetings tugnuts.
I have a 2013 R21EC. I’m installing a new Garmin chart plotter. Have chased back where the old Garmin 700 series chart plotter cable splices into the main boat wiring harness below the dash.
Where the two are spliced together, the wires coming from the main boat harness are as follows:

• 2 yellow wires (looks like grounds)
• 2 red wires
• 1 blue wire.

These wires all splice into the old Garmin cable which terminates in a 19 pin connector on the back of the unit.
I can figure out a pos and neg (red and yellow) for the new Garmin.
Can anyone tell me what all the wires coming off the main boat harness are intended for?

Thanks so much for any replies!
Cheers,
Steve
Gabriola Island B.C.