T25 clocks are generally fine but don't like being removed too often due to the wealknesses in the plastic circuit, connections, and general wear and tear. Strangely I was looking at this problem myself today and just passing on my thoughts here. Purists needn't read further.
Lots have hardwired their dash due to similar probs but I'm minded to build a new set of clocks in the longer term but only once I've tested each guage to make sure everything is accurate. Firstly the connector to the clocks wants changing. Ideal candidate would be the ATX connector used in PCs to connect the power supply to the motherboard. Theres 20 connections on these and both male and female versions are available (£1.69 each at Maplins). That should put an end to the poor connection problem and allow numerous additonal feeds as required.
Finding a rev counter with the additional guages such as temperature isn't easy inless its LCD and then you have extra probs sourcing sensors etc. That said, theres no reason (as far as I can see) why a new interior dash assembly couldn't be built from scratch. I've just ordered a blue back-lit volt meter from China (£7) as a start towards this. They also do digital temperature guages and other goodies (again cheap) Monitoring overall battery status seems a useful addition for the driver so thats definately going in. The dash doesn't need to be complicated and could I guess retain the original speedo (or at least the milometer) but a rev counter is damned useful and doesn't HAVE to be an original T25 one in this context, as along as you cut a slot/hole for it. The existing flimsy crappy circuit can be replaced with a more solid-state veroboard or even designed/etched version that would suit lots of designs and the lights all converted to LED.
Reference for different displays:
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Some time back, I actually removed my bulbs and holders and stuck a blue neon tube to the underside of the dash cowling, right above the holes where the bulbs were and it transformed the illumination of the clocks but all in all the T25 dash is no 'looker', traps dust (and in my case rolling tobacco) and a more customised pod would do wonders really. Somewhere on the net is a set of Audi clocks converted to fit a T25 and it looked pretty good but I think I'll aim for a setup that covers all the areas I actually need to know about and make an easy-clean assemly to suit these. Off the top of my head, I have a plan for something similar to the panels in Star Trek next generation (ie black until ignition is on). All sounds a little far-fetched I know, but I won't be the only one who will have mused all this.
Worth bearing in mind too, that you can get cycle speedos which use a wheel sensor and go up to at least 99mph, which not many of us are likely to achieve so that may well be fine as a speedo if backlit.
Lots of ideas here. Done my bit. Anyone else?