Instrument panel

To get at the blower control lever, I needed to pull off the instrument panel. Conveniently, there are only 4 simple retaining screws. Less conveniently, the speedo cable prevents the panel from moving more than about 1.5" (just enough to get my - fairly small - hand behind). Neither the Haynes nor the Brooklands manual say how to disconnect the speedo (Haynes just says "disconnect the speedometer cable"; Brooklands has the positively loquacious "if necessary, disconnect the speedometer cable").
After some experimenting I was able to master the correct ninja death grip necessary to pop the cable housing: note that you need to squeeze the big ring right where the cable enters the dial not the two raised bridges further back on the connector housing.

With the speedo cable off, you can work the panel around and down below the steering column. Once in there I found a few mystery wires:

• brown yellow (NY) and brown-white (NW) wires from one of the 'spare' lamp locations beyond the glow plug indicator going down towards the hazard/fog switch panel. NW appears to have a resistor inline
• brown-white (NW) ending in an unterminated butt connector
• two green-black or green-slate joining in a free male spade connector

I couldn't see anything obviously amiss with the oil temp gauge (which seems not to work) but I found a broken-off lamp housing on the water temp gauge. The green lens cover had snapped and partly fallen into the gauge housing. After some fishing around with circlip pliers I was able to haul the bottom part up and tack it back onto the inside of the housing with a smear of cyanoacrillate. I then built the whole thing up and attached the top part with epoxy.