By your iRV2 profile I'll assume your 3302DS is built on a Ford F53 chassis.
Two caveats on the following advice:
1) A coach manufacturer can alter wiring as he pleases, and
2) I only have Ford documentation on CD for 2006 and 2007
On that last point, the Ford Body Builders Layout Books are online
, and here is a link
to the electrical information from the BBLB for the 2002 model year F53. It looks enough like what I have for 2006-2007 that I'm fairly confident in my information and advice given below.
Ford provides two connectors inside the left rear frame of the coach, in your case about six to eight feet from the end of the coach. Those connectors contain these signals:
Ford connector C405:
2 TRAILER LEFT TURN W/ BRAKE SIGNAL
3 BACKUP LAMP
4 TRAILER GROUND
5 TRAILER RIGHT TURN W/ BRAKE SIGNAL
6 INTERIOR LAMP FEED
7 TRAILER BACKUP LAMP
8 BRAKE LAMP FEEDS
10 PARK LAMPS, REAR
11 RIGHT TURN SIGNAL (ONLY), REAR
12 ELECTRIC BRAKE POWER
Ford connector C406
1 TRAILER RUNNING LAMPS
2 LEFT TURN SIGNAL (ONLY), REAR
3 LEFT TURN W/ BRAKE SIGNAL
4 RIGHT TURN W/ BRAKE SIGNAL
Everything is there to run both the coach and trailer lights. Although a converter may be present, I don't believe one is needed.
If it was I, I'd do what "Dutch Star Don" suggests and trace the wires from the two connectors to the rear, so I'd understand what's connected to what. That by itself should reveal the cause of your current problem. Then I'd replace the fragile-looking 4-wire connector with an RV-style 7-pin connector bolted to the hitch/bumper, using the correct wires from the Ford connectors. This will give you additional signal pins, including the 12V charge line and the "blue" trailer electric brake wire.
Finally, as an observation, when odd crossover effects occur it's often because of missing or poor grounds. Check to see if both the coach and towed vehicle/trailer wiring grounds are solid.
I'm willing to troubleshoot this with you over e-mail or telephone. If you're interested, send me a private message with your contact information.