Garmin wire colors

[Beer van Huet]

I have a Garmin Zumo 590 and want to connect its MP3 player to my external (Rumble Road) speakers. Because I rearranged all my wiring and don't want any bulky jacks or plugs in it, I cut the (speaker) output jack from the Garmin connection lead to find 4 wires. Brown, Orange, Yellow and Violet (Purple).
The speakers have a 12V, ground and Audio (L/R) wire.
When I plugged the speaker jack in the Garmin (female) jack, they were working fine.
Now that I want to connect (solder) the speaker wires directly (without the plugs/jacks) to the Garmin wire, I am having difficulty in determining the right wires.
I spent some time online trying to figure this out, to no avail. My Garmin dealer does not know the answer and does not have a wiring diagram or schematic.
I also measured each wire’s resistance.

It looks to me like Yellow is some sort of telephone connection, not for MP3 music.
There must be a ground as well.
The resistance of Brown, Orange and Violet changes when I start my player.
I tried to connect all the possibilities with my speakers accordingly, nothing happens however.
Would somebody be so kind and tell me which color Garmin wires to connect to my speaker wires.
Or perhaps make any sense out of the above table?
TIA

[Beer van Huet]

Guess what,

I contacted Garmin US this time and they forwarded me back to Garmin Europe.
The color and function of the wires and 3.5mm audio jack connection will not be disclosed to customers. I guess Garmin either thinks the connection of a simple 80 cents 3.5 mm audio jack is rocket science and a state secret, or that I am trying to copy their latest model, LOL

[Beer van Huet]

As it turned out, I used the wrong color wire to connect my speakers.  As a matter of fact, the Rumble Road speakers have 3 wires:

Red is audio
Grey is 12VDC
Black is mass/earth.

I presumed the red wire was the 12V wire and reconnected them that way. Fixed that now by using the Grey wire as +
Connected the speaker audio to the Garmin Brown and Violet wire and getting a great sound.
It does not make any difference if I connect Orange to mass. Yellow will stop the MP3 player, it must have another function.

What have I (re)learned from this?
a. Don't take the red (+) color wire for granted
b. If you mess around with a lot of wires, marking them is not such a bad idea,

[BigM]

I had thought about disc. cutting off the cig. lighter plug and wire straight in hot and grd. . Know what color wires would be for that?