I have a Fiat Ducato based campervan.
The keycode light stays on with all my keys including the master red one.
I suspect the immobiliser or a broken wire. Am I right?
Fiat want 100 + VAT to take immobiliser out.
I am not keen as it will leave vehicle unprotected.
Alternatively, does anyone know how to take immobiliser out or replace it or suggest any alternatives?

have a look at the immobiliser antenna (Circular plastic loop) on the ignition barrel. if it's not damaged, Check all the fuses in fuse box. other than that, may be a loose wire somewhere.

Welcome to the forum!

Is adrenaline brown?

Thanks for that.
I looked at the antenna - looks OK
All fuses are OK.
One thing peculiar.
After I jiggled the ring antenna slightly then turned key the light went out and the engine started.
On starting again the same problem occurred.
What do you think?

Faulty antenna wiring possibly. worth having a look at the Ignition barrel wiring connectors to make sure they are connected securely. If the connectors looks fine, then the immobiliser is at fault. Make sure the wiring to the antenna ring is secure and check the whole wire for cuts and damage. Possibly a loose wire if it starts when jiggling it.
USE THE BLUE KEY when doing this as the RED KEY opens the ECU memory to store new blue keys and the current ones may risk being erased if you are using the red key to diagnose your problem.

See this thread https://www.fiatforum.com/forum/topic.asp?TOPIC_ID=1927 although it's for a Cinq, the immobiliser systems are relativeley the same. It basically explains the bit about the keys

Hope all this helps

Is adrenaline brown?