I was talking to the chap who services my 'main' cars earlier this week. He has been in the trade for a good number of years and been building up his business steadily, really reliable and honest, and he was talking about the way the ever-encroaching digitisation of servicing, MoT testing and so on is slowly but surely having an effect on driving out the cowboys and dodgy scams etc (remember the old pads of blank MoT certificates? He reckons they used to get nicked and sold down the pub for £50 per sheet. At 100 sheets per pad, that single pad was worth £5K on the black market).
(Stay with me, there *is* a point to this waffle!)
One of the things he told me is that MoT testing is now linked IN REAL TIME to the main VOSA/DVSA computers, and their inspectors drive around the country checking up on garages. When a car is up for MoT test (sorry all you up to speed guys and gals who already know all this) the tester has to enter the reg number into the computer. The inspectors know how long each part of the test takes, and what order the test should be done in. So they sit outside in their car, monitoring the unsuspecting MoT tester as his test car goes through each stage...
Let's suppose that after X minutes the tester should have the car hooked up to the exhaust gas analyser. At X minutes, in walks Mr Inspector, unannounced, to check that the test car really is hooked up, and not the nice shiny new car parked next to it, to give a clean 'pass' reading...
If the inspector finds the right car isn't being tested, or finds something not going according to the prescribed procedure, the garage can lose its MoT test licence on the spot.
The net result of this tightening up is that (except for remote Scottish islands where the Inspector would be seen coming before he left the mainland!) MoT testers are sticking more and more rigidly to the letter of the law. Now, what has this got to do with your speedometer.... ?
My point is, one of the fail points is "not illuminated". A speedometer must be readable in the dark as well as daylight, and so the internal bulb must be working. But if you simply stick on a circular mph scale marked on a piece of card or other material that does not transmit light, then although you'll be able to see the speedo needle, in the dark you still won't be able to see what speed figure it's pointing at - and the MoT is a fail.
So as well as getting the scale marked in mph, you'll also need to ensure that there is some means by which it can be seen in the dark - some dedicated adjacent lamp like a number plate lamp, perhaps, but whatever it is, just sticking on a piece of white cardboard alone runs an increasing risk of being rejected.
