Immobiliser issues

My 1993 Disco 1 200Tdi has developed an intermittent fault where the immobiliser comes into action at will.

I discovered one of the electrical joints under the steering head cowl to be suspect so have re made the joint using connectors. Now even though the joint is good the immobiliser activates without setting it using the key fob.

The original joint was soldered, should I have re soldered rather than use conventional connectors?

For all connections solder where you can unless there is a reason that you might want to unplug it. It's just more reliable

Resolder soldered joints. be wary when soldering crimped joints as solder is more likely to suffer stress fractures.

You don't have a passive immobiliser, you have two ways to set the immobiliser, when you turn the key in the drivers door lock and locking with the fob it's the same to unset.

Got the soldering iron out and remade the connector joint also found another fatigued solder joint and remade that too. All done and dusted no problems with the alarm/imobiliser circuits.

Simples innit.