I had several issues on my dash electrics, some tips from me to you all:
Have a tin to put your bits in!
Remove driver seat .. this made access better and protected seat - takes 2 mins
Start with speedo, put hand behind and remove the knurled knobs
Remove bulbs to speedo
Remove speedo cable
Remove speedo dial, this gives access to rpm dial
Remove rpm knurled knobs
Remove wires etc
Now at this point you can decide if you unscrew wooden dash, I did but you can get access to most from here if you have small hands! Also then you can remove and clean and test hazard switch
Download and print the wiring diagram , so do your fault finding and photo and record as much detail as you can. My TR had a lot of recut wires, some wires not truly corresponding to wiring diagram and fitted with a differing hazard
Check , clean and replace when necessary every connector, use a electric grease or similar on all connectors, make sure they are nice and tight and wont fall off when revving, hopefully this is it for 10 years plus so dont rush this time to do good maintenance. Also mine had loads of yukky old electric tape everywhere, remove, clean and use something better
Consider bulb replacement, they degrade over time (i personally dont like LEDs on classics . . personal choice, like food and women :-))
Oil speedo and RPM cable, replace grommets on firewall
Clean and check earth points . . they are connected to the bash on the knurled stems.
Test all before refitting, I made some extension wires so that I could test hazards etc with dash out.
Use some small zip ties, clean up inside when your happy on functionality
Put dash in
Put illumination bulbs back into RPM dial, the bulb should reach
Put RPM dial in, then if you can lay under with a pillow and connect spades on stem which hold dial in, and add knurled knobs, dont forget earth cable. Then speedo cable and the two bottom bulbs (flasher and hi beam). I found laying down and having a decent flashlight really helped here
Check the function, then do same on speedo, same process
test and test . . and write as much down as you can - what seems obvious now wont be next year . . . . . all that you have learnt is now draining away!
Hope this is of use and maybe others have additions.