No driver side turn signal Roadtrek 07 190

[CareyM]

problem: 06 chevy 3500 chassis w/ 07 Roadtrek 190 OEM mods of OEM Tow and trailer package (including heavy duty turn signal flasher upgrade.) I am getting a 'fast click' noise when i use the turn signal arm on steering column (which usually means nonworking bulb.) lack of driver-side rear turn signal started when i was towing a 25 ' boat trailer during hurricane zeta in 11/20. 2/ all fuses checked good, all lamps in rear are good, grounds into all rear driverside lamps look good, no broken hot / ground wires, etc. )
--note Inside fusebox P. 394 chevy 3500 manual (box under RT's driver seat ) has #4 left rear STOP/TURN and #6 rt rear stop/turn.
--engine compartment fusebox p 396 of chevy express manual shows 2 more sets of fuses controlling turn signals : engine fuse box #9=rt daytime running and turn, #10 = left daytime running & turn sig. and #17= trailer stop/turn.
past diagnosis efforts without success: D/Side and pass side fuses= OK (in box under driver seat and in engine compartment box.) all lamp bulbs front and rear all good.
1/ we know turn signal arm at steering wheel works fine to operate both rt and left turn signals on front and rear. since only the rear passenger - right side turn signal works and left TSig lamp remains dark and doesn't, amps supplied by yellow hot wire into d /side rear TS lamp is suspect. i suspect a worn or crimped wire supplying rear left T Sig. amps. right TSig (green hot wire) work on both driver side and passenger side rear. (so it's likely that this driverside rear T Signal nonfunction is not caused by a problem in this 152$ turn signal arm chevy part.. QUESTION: is a further diagnostic i could run on the inside of this arm to test for proper current coming out of TS arm into rear driver side only turn signal circuit ?) )
2/ i am suspecting a loss of sufficient current from the TS arm into inside d/side TSig fuse #4 then out of fuse #4 into the d/side rear turn signal bulb #3157 circuit. (bulb needs 4 to 6 amps to light.) I can measure amps coming out of d / side turn sig fuse # , if those amps are good then the problem is between the inside fuse box and the rear d/side t sig lamp.(HOW TO CHECK THIS ? CONTINUITY CHECK ? )
3/ before i start ripping out the ceiling and upholstery to access wires from the fusebox past B panel and into driverside rear, can anyone suggest some additional tests ? (fluke ac dc clamp on model 374 .))
4/ in the past, my 210P 05C had a loss of current into the rear driverside backup light while the pass side rear backup worked fine. using my fluke, i measured 5 amps into working rt pass rear lamp bulb and only 1.7 into left driverside rear -- not enough amps to light the bulb.). a RT tech told me the scotchlock connector RT used to connect hot wires coming out of inner fusebox into rear of van often failed. wires ran out of fusebox then up along the B pillar then to the back lites . those hot wires' 'scotchlok connectors' often failed, or the wires got crimped or deteriorated w/ age and wear. this leads to an under supply of current to the bulb. if not enough current comes through the hot wire, you get nonworking bulbs on one or both sides of the rear. RT suggested a jumper of hot wire off the working rt -side rear light to suppply the nonworking leftside park and backup lites. (that worked fine as it was a common hot 12v supply for both rear d-side and rear pass- side.NOW the turn signal current supplies are independent hots. ALL THOUGHTS WELCOME !! or do i have to rewire the driverside turnsignal hot wire from the fuse box #4 all the way to the rear?