you can go to Jensen and get the manual that gives you the wiring guide for the radio.
http://www.jensenrvdirect.com/manuals-guides
You would need ohm meter to ohm the wires. Look for wires that might be paired together in some manner. These are generally the speakers.
Trailer wiring is usually two wires that are joined via the molded insulation. Usually have some color such as blue or red or purple on the wire. Might be a stripe might be solid color. The other wire will be white. The color wire will the +12v and the white wire ground.
On the radio, Red is usually power. Yellow is usually a constant voltage wire so you retain memory settings on radio.
Gray, green, pink, purple, etc (some may have a stripe on them) are usually speaker (+) wires. Black or white can be the speaker (-) wires.
I would disconnect shore power and trailer batteries before doing any ohm checks. I would short the battery 12v and the ground together to id the 12v circuits. Lable the wires and then go "un-short" the battery 12v and ground to prevent any problems should you apply shore power accidentally.
I would look for wire pairs and check for some low ohms like 4 or 8 ohms between the wires. This is usually a speaker. You might hear a hum or crackle when you ohm a speaker but if not, you will need to send some sound signal to that wire pair to id the location of the speaker.
You can order an accessory kit to get the Jensen plug or buy a new radio with associated accessories to get speaker/power plug(s)
http://www.jensenrvdirect.com/servic...he-awm965.html
JMHO.....hope this helps.