1975 Gt 550 standard regulator/rectifier change

[pfg49]

My regulator has stopped working, so rather than messing about with an electro/mechanical device, can I fit a modern electronic universal 5 wire combined unit? If so, where does the alternator excitation feed from?

[Alan H]

The regulator.
That's what it does. It regulates the current to the rotor (excitation windings) to limit the output of the alternator as the battery approaches fully charged. As the battery voltage drops, the regulator allows more current to the rotor and makes the alternator develop more output to charge the battery more.
The original regulator works fine, and probably only needs the points cleaning gently, and then adjusting to provide the correct setting for changeover from high to low charging at about 14.2 volts or so.
You can fit an electronic one, but the originals seems to work just fine when adjusted correctly.
Remember to ensure that if you do fit an electronic one, that it gets plenty of cooling air around it or it will heat up and knacks quickly.