The wire to the switch wasn't always fitted (my 90 never had it from new) but it should be in the dash harness. Look for the white/yellow wire in the multi-way plugs near the brake servo/clutch pedal. If necessary, run a new wire from there down along the gearbox and through the back of the handbrake lever. Mine didn't have a switch either, so rather than bodge something up I ended up replacing it with a take-off part from a much newer Defender.
@FlyingPete
If you have a tilted truck on the cluster this is a rare cluster.
Is yours ex military ?
@FlyingPete
If you have a tilted truck on the cluster this is a rare cluster.
Is yours ex military ?