If yours is a Bargmen, this may be the one for your switch. Gene's pic sure look like a Bargmen and Sunline used Bargman on both of my 2004 TT's.
Replacement 48" Cable for Breakaway Switch Bargman Accessories and Parts 54-85-002
If there is a model number on the side of the switch we can maybe find it better.
Scroll down a little bit here from the Bargmen site
Breakaways - Bargman
Auto parts (NAPA) stores may have these as well. The Bargmen switches are a common trailer part.
Once a year when the trailer is unhooked from the truck, (important to not have the 7 wire plugged into the truck when doing this, can back feed the brake controller) pull the pin out and spray the O ring with some silicone. Over time the O ring gets stuck in the switch so hard you can rip the cable right out of the eyelet trining to pull the plunger out of the switch.
Hope this helps
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
Google Custom Search For Sunline Owners Club