Some one has offered me a nice +ve earth Rev Counter from the 60's - is it possible to alter such things to -ve earth or not???? If not I may just put a modern cheap unit in the shell of this Rootes tacho. Cheers B
Yep, out of a Humber Sceptre - really nice looking clock - haven't got a pic but will show if I go for it!
You need to make sure the casing of the rev counter is insulated from the chassis of the bus so you can connect it to positive when you fix it into the dash or wherever. Depending on how the pickup for rev counting is done you might be able to simply wire the pickup wire to the coil - if the dwell angle is about 45 degrees then it doesnt matter which way up the signal is because the points are open and closed for the same amount of time. Otherwise it might take some trickery. So the answer is , connect it up with the power the right way round for the rev counter and connect it to the coil. See what happens. And if it has a nice 270 degree meter movement driving the needle, you may also be able to swap the meter driving electronics for something more modern without having to lose the retro front panel or needle.
Stick an KGB rev counter in - I did, it's the right polarity and it works with a 4 cyl engine with the trigger taken off the -ve side of the coil. Looks good too and it's 80mm diameter so it fits the blank.
The illumination of the Tacho may well be in the form of a single lead lampholder that cannot just be hooked into the existing lighting circuit.
