Problem with mk3 gti help me before I burn it

[dannydubs]

   

I've brought a R reg gti and think I've mad a mistake
When I brought the car it had 2 ignition barrels one in the footwell which was being used to start the car with its own key And the immobiliser ring from the original ignition had the original key taped to it
And the started fine

I asked the owner and he said that he had the replaced all locks including the new hanging ignition
To try and use one key for whole car as was using different keys for doors etc

Right so what I've done is plugged the original ignition back in which is still in place put the original immobiliser ring back on and tried to start car with orignal key and won't start turns over but doesn't  fire up
So I put it back taped original key back to ring plugged second ignition back in Tried to start it again nothing???

So because I've took original key away from the immobiliser could I have decoded the key?
Even tho surly you take you key away from car every day

Dnt no what to do now
Sorry for my crappy explanation
please help or ask me if not understood?

[ToddyGTi]

You can't decode the keys so don't worry about that.

By the sounds of it it's just been wired badly. Why don't you remove the ignition barrel that you don't need, replace it with the new one. Put the transponder ring in the compartment in front of your knees (service book holder) with the original key in it. The only other way is to take the chipset out of the old key and put it in the new one but you might have to recode it if it loses power iirc