LHS switch on 1982 KZ750 Ltd

Hi Guys.
im just in the process of renovating a1982 KZ750 Ltd. I have a question regarding the indicator switch on the LHS. When I slide it to the left or right, the lights work fine, but if I release the switch, it returns to the centre position and the indicator lights go off. So basically in the present condition, to turn in either direction I would need to physically hold the switch open. The Clymer manual says a 4 second delay should exist from initiation of the signal to it turning itself off, or 50m travel, which ever happens first. Can anyone tell me whether the problem is mechanical (with the switch) or is it an issue with the relay? On my other bike (Yamaha SR500) the switch stays in the position you turn it. 
I’d really appreciate understanding how this switch should work when in proper order. All help and advice is most welcome.

thanks

I have a 440 Ltd which has the auto cancellation turn signals as well. 
I gutted my turn signal system though as I ran a Safer Turn System for awhile until it got weird and I took it off. 
Your issue may be mechanical. 
What may be happening is the solenoid in the turn signal switch housing may be stuck and it's causing the switch to return to center when you release pressure. The switch is supposed to stay where you put it until the control unit activates the solenoid in the housing and the switch springs back to the center position. 

There is always a possibility that the solenoid is constantly energized causing the turn signal to center automatically. Which makes the problem electrical. 
If you have a compass app on your phone you can check the solenoid. As the solenoid is an electromagnet, when the solenoid is on it will spin the compass. When it turns off the compass will return. The only thing that may thwart you is that the solenoid is within an aluminum housing. Possibly shielding the electromagnet.

Open up the switch housing to see what is amiss. 
The solenoid should be the in the cylinder-looking portion below the turn signal switch. 

There's a KZ750 4-cylinder FSM pdf available. It's probably here on KZRider somewhere. either in the filebase or in any number of topics.  I don't know if it's more detailed than the clymer manual.  from the FSM. If the system does not function right, check the connections carefully, then inspect the distance sensor and T.Sig. switch/solenoid.  If those check out, replace the T.Sig. control unit.

Thanks so much for your help.