1985 C10 door lock actuator works both ways but won't stay down in locked position.

[RikL]

Hey all! Please help, 85 c10 power door lock moves to locked position but won't stay down. Is this the actuator failing or possibly a bad relay?

 

[RikL]

Update, removed pwr connector to actuator, same thing. Are these actuators spring loaded or is something else causing it to spring up?

 

[HotWheelsBurban]

Update, removed pwr connector to actuator, same thing. Are these actuators spring loaded or is something else causing it to spring up?

The actuators can get stuck in the Lock or Unlock position. Maybe yours is in the process of going out? I think there is a spring inside it that the solenoid uses to pop the plunger?
I had this happen on my C3500 OBS Crew Cab longbed; what I did to make the locks work manually was go into the door and pull the lock rod out of the actuator. There is a short bar that goes from the horizontal lock rod, vertically into the actuator plunger arm socket. You could probably cut the bar off, but it's hardened steel and I wanted to be able to have functional power locks after replacing the actuators.
Unfortunately it's been too many years since I've been inside a square body door so I don't know how similar it is to the newer trucks. Maybe these pictures will explain more?

 

[NLD79K10]

It could be a dying actuator that can no longer fully pull the latch into the locked position, poor alignment of the actuator and/or linkage or just a weak power feed to the actuator.
With the fact that it does so even when the power isn't connected, I'd start looking at the linkage first.

 

[RikL]

Thanks for the info!