Stuffed starter motor?

Hi Im getting 12v across the starter (solenoid) terminal when the ignition is OFF but only around 1-2v across it when it is on! The truck wont start obviously, I'm just trying to figure out what the correct voltages should be- In my mind, there should be 0v across it when the ignition is off and should only be energised (12v) when the ignition/starter is turned on.

The truck is a farm hack- 86 Nissan 720 and the starter part of the ignition has been replaced by a light switch.which is what I think has caused the starter to die: Being left 'on', the solenoid has burnt out.

Can someone confirm what the various voltages should be for each stage please! (Ignition on, starter on, ignition off)

Given what Im seeing, I guess it is shorting.

ummmmm your voltage sgould be 12.56 or higher for a calcium battery. when you start you say the voltage drops to 1 to 2 volt!
if that is the case. then you can throw your battery in the rubish as it is dead obviously.

you will also be able to mesure thsi drop right at the battery if its poked.

the silanoid is activated there is 2 therminals one is small and that is the power that should not be existinguntill ignition is on, the other is big and is a big cable permanetly connected to the battery without a fuse the big one always has power on with ignition on or off. so all your info tells me your battery is dead.

Testing to do on a solenoid is relatively easy provided you have a digital multimeter.
As intrade said the small terminal only activates when the key is turned and must have at 10v min to operate the solenoid.less than that usually results in a chattering machine gun noise.
If you then place the multimeter on the +ve terminal of the battery (Set it to 0-20v) and the large terminal on the starter motor and get someone to crank the engine this reading must be LOWER or LESS than 0.2v, if it is higher then there is a resistance fault in the cable / connection. You can repeat exactly the same test on the -ve side of the battery and where the earth cable is bolted through the starter and repeat. If all good then battery is undercharged. Whatever testing you do with voltages must be the same as the voltage across the battery terminals.simple as that.
To further narrow down a solenoid fault then you will need to measure current flow through the wiring which requires an inductive type ammeter

Hope this helps.

PS = The largest killer of solenoids is the driver holding the key on for too long with a starter motor not turning.burns / shorts out the wiring.