The MGA With An Attitude

123 Electronic Distibutor This Distributor from 123 Ignition has a side port for vacuum signal input for the vacuum advance function. The 123\GB-4-R-V model has 16 pre-programmed advance curves presumably suitable for most British cars, from which you may choose one by switch selection. You can download the instruction booklet from the 123 web site.

This one has a 2-wire hook-up for 6-volts or 12-volts and must be run with negative earth electrical system (easy enough to convert your pos-earth car to neg-earth). For some time past the rotary switch was on the bottom face of the housing so you had to R&R the distributor to change the advance curve setting. The switch location has since been changed to the side of the body so it can be adjusted without moving the distributor. Instruction recommends changing the cap and rotor every 30,000-km (18,000-mi). The cap and rotor have Bosh part numbers.
123 Programable Distibutor
The 123\TUNE model can be programmed for two sets of curves of your specification that can be selected (for instant change) with a 12-volt signal. You can download the instruction booklet from the 123 web site.

This one has 4-wire hook-up and can be used with either positive earth or negative earth 12-volt electrical system (except for 8-cylinder models which are exclusively neg-earth). It can be re-programmed via the USB cable while in the car. It includes a rev-limiter function and a boost/retard function (for supercharger applications). Diagrams below show how to connect three wires for positive or negative earth. The 4th wire (yellow not shown) is used to switch between 1st and 2nd programmed advance curves.
123 Distibutor Hook Up

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