Breakaway switch not working... and maybe brake issues

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Regarding a 2001 TM 3023...

Problem: Pulling the breakaway plug out does not engage the brakes - the trailer still rolls fine.
... AND... I get an intermittent "trailer not connected" on my brake controller panel. Yet all interior and exterior lights work, AC plugged in works, DC works when AC not connected, appliances all work... all other electrical has worked since 2001. Except: until recently I never got the "trailer not connected" message.

I'll stop there for a moment - any suggestions just from that? Checked undercarriage wiring - nothing frayed etc., trailer battery is good - 13.2 V , and trailer brakes work when I use the truck brake controller. (except for a possible problem I'll mention below)

Continuing on... Pater C has a good picture of brake wiring:
https://www.trailmanorowners.com/for...0&d=1582075325(Sorry, tried to put inline but came out way too large. Is it OK to reference someone else's pic if I give them credit? if not, just say the word.)

Using that picture for my driver's side brakes, the 2 black wires are just pigtails, not connected to anything, not capped... nada. They are supposed to connect to the passenger brakes, right? And if they are not connected, have I only ever been engaging the driver side brakes? When I test the brakes, someone next to the driver side signals pass/fail and I never check the passenger side separately (believe me, that's not nearly the dumbest thing I've done with this trailer...oh the stories!).

However, the unconnected black wires problem seems like it would NOT be causing the breakaway problem... right? Maybe I've got 2 problems? 1) Pulled breakaway not engaging brakes AND 2) passenger brakes not connected.

I'll keep looking but please make suggestions if these issues ring a bell. Thanks in advance for any/all help.

And while I'm asking breakaway questions: Would checking voltage on the TM trailer electrical connector brake terminal be a reliable test to see if the emergency braking is working? My thought is that I should read 12V from brake terminal to ground when the breakaway is pulled and 0V if it's plugged in, but maybe there is something preventing flow into the TM connector? Any other electrical ways to check the breakaway working without actually driving forward and checking for brake movement? I only have a voltmeter with pins, not a clamping meter, and at what looks to be $100 minimum for a decent clamping meter, I'm just trying to get by without.

Anyway, thanks... hope you're all enjoying the 2020 summer.