Today I completed the gear select back lighting.  My first attempt was to use a bright LED fitted in the standard bulb socket and bent at a jaunty angle to get as much light into the diffuser as possible, but this ended up just as pathetic as the original bulb.
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So I decided to light up the symbols from directly behind which involved removing a bit of paint from the diffuser to the rear of the N and D.  The P and R have no paint.  Then I wired up some SMD LED's to test the theory and these were a marked improvement when place directly on the diffuser.
The pics below show how they are wired.
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The next stage was to wire four LED's to a section of veroboard with the relevant bias resistors fitted.  I shrink wrapped the board for protection.
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To fix the LED's in place on the diffuser I didn't want to use a glue of any type as this is rather experimental and some LED's have a habit of failing fairly quickly, so I came up with the idea of using a length of very sticky insulation strip which happened to be the exact width I needed, and I carefully laid them up in position.
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Then a final test before refitting.
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It was then just a matter of fitting a couple of bullet connectors to the wiring and putting it all back together.
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Hopefully the LED's will not fail too quickly as it's a bit of a faff removing it all.  Time will tell.