Manual electric trim not working

[Tommy]

81J with KFC200. Gone into annual working fine but now manual electric trim isn't working. The avionics guy actually said it was working ok when he first started working on the biannual instrument check. 

There is a distinctive humming in the tail when manual electric trim is engaged (both red and black switches) both up and down but the trim wheel isn't turning at all. Autopilot electric trim is working and runs through the entire trim range. The red half of the switch will disengage the A/P but I can still hand turn the wheel with it pressed.

Had the feeling that there is a drop in the voltage somewhere along the line between the yoke trim switch and solenoid that engages (pulls down) a gear reduction assembly from the trim motor to the trim tube.

Am I on the right track? If so, is someone able to point to me where to find places like amp connector locations that connect the wire from switch to the solenoid to put a voltage meter on? 

Thanks! 

ps. The avionics guy isn't going to fix this for free and said might take a day or two to find where the fault is and I am flying next 48 hours so hoping to see if it's just a frayed wire or loose connector somewhere  

[N201MKTurbo]

It sounds like the engagement solenoid is not engaging with the switch. The fact that it engages with the autopilot means that the wiring and the servo are OK. I would look at the wiring between the disconnect relay and the yoke switch. 

I'm not a KFC200 expert...

[Tommy]

Can it be the $witches?? 

Or most likely the wires?

I am leaning towards the wires because the switches had never given me any problem. I guess we just have to trace it from the switches all the way to the solenoids?

Where is this disconnect relay normally located?

Thanks @N201MKTurbo