Had a chat with the local bod at Maplins (prob same as your Tandy).

You can get small switches which are operated by the depression of a spring loaded ball, (imagine the latches for cupboard which have a large ball bearing spring loaded).

My thoughts on how to build a cheap electronic timing tool would use the MB static tool with the spring loaded centre removed. Replace this with the above ball operated electric switch insulated from the tool outer but with a positive feed going to the switch.

You would need to get the depth just right, to do this set pump up with old tool first so as notch is directly centred then calibrate the depth of your spring switch which needs to be glued in place.

Fit a small bulb and power source which is earthed to the chassis and this should then do a similar job.

The only thing I would say is it won't be anymore accurate just convenient and a lot quicker.

__________________
David


1996 Mercedes S124 E300TD - 129k - rolling restoration project -

1998 Mercedes W210 300TD - 118k (assimilated into above vehicle)