I have the same Dolomite base as you - the pull switch is suspect - first: loosen the red switch cover (unscrew) and work in in and out a few times - this allows the switch contacts to move over a greater distance. Second: unscrew the red cover, and unscrew the switch from the dashboard - disconnect via the six pin plug that is about 75mm down the wires , and try some switch cleaner. Third: buy a new switch from Rimmers 159905A (£50)
i've totally rewired my car - running earths from everwhere - there is a lot of uneccesary wire in the loom (heated rear windows, boot light, courtesy lights, heaters) etc. also there is a Night dimming relay in the rear brake light, and indicator circuits - i suggest you throw that away - it has 6 terminals - just link the wire from contact 3 and 6 together, 2 and 5 together, and 1 and 4 together. this dims all the rear lights when you turn the headlights on
The circular warning light cluster works well, but has 'interesting' internal connections - work to the original wiring diagram and its fine - alternatively just pull the plug off the back off the cluster its about 50mm in diameter - i can send you the wire numbers to connect to individual bulbs - only one queston -does the cluster have two individual turn lamps or one dual turn lamp
where are you based - i'm in Clithere, Lancashire, and have suffered most of the problems that the dolomite mechanicals/electrics can throw at you.