12-13V is what you should see across the battery, the question is what happens to the voltage when you hit the start button, and just after?
See post #10 here
http://www.ukmonster.co.uk/monster/s...ad.php?t=58310
Does the solenoid click once or click-click-click until you release the button?
I agree with Luddite, if the bike ran ok when restricted, you’ve removed the restrictor and it now won’t start then it sounds like you’ve dislodged something.
I take it the “funny yellow seal with a wire through it” isn’t electrical and connected to something else, it’s just a tamperproof indicator like your electricity meter at home?