Thanks for the advice, very helpful.

I've uploaded the new schematic that I built in Isis, 'solenoids 2'. The 2 logic toggles are there to indicate pins from microcontroller.

https://sites.goo...schematics

I have 12V supply that energises the relay when the ULN2003 o/p pin is low - acting as ground.

The motors are there to indicate solenoids.

My problem is if I wire positive end solenoid to one side of the relay and ground the other side, do I need a supply in this loop to power solenoid?

Correct in saying,

1. relay off - nothing happening
2. relay activated
3. tubular solenoid works as long as 12V battery placed in series with it (in relay activated loop)

Ideally when energised the door would be locked, ie most of the time so a continuous duty solenoid required.

Thinking something like this http://radionics.rs-online.com/web/p/tubular-solenoid/5336916/