VW golf mk3 ABF starting problems

[little-ii]

just bought a abf engined mk3 ready for a engine conversion into my mk2. when i bought it started fine every time. ive stripped the interior out and now when i go to start it everything lights up but when i turn the key all the way it makes a clicking noise. it wont start unless a battery booster pack is used and even the nothing happens first few turns of the key. once it starts if i turn it off sometimes it turns back on then sometimes it doesn't. tried using a different battery but no look. all i can think of it being is an immobiliser problem or a crankshaft sensor issue.
any help will be appreciated. thanks 

[Screech16v]

Could be a ignition switch problem,it's a very common fault,or starter itself.

[little-ii]

Could be a ignition switch problem,it's a very common fault,or starter itself.

could i try the one of my 90 spec mk2 and see if thats the fault

[Screech16v]

If the switch fits the plug then yes try it