Alternators can have two different winding connections and maybe 3 different rectifier arrangements, but tachos aren't usually very fussy on the actual waveform, so making a connection isn't hard.
Depending on how it's built, you'll probably need to remove the vac pump carefully, then separate the housings, taking the stator with the rear one. Try not to damage the windings.
Once it's cleaved in half, undo the little nuts or screws holding the rectifier plates in the housing. Be very careful not to lose any insulators/washers.
Find where the windings are connected to the rectifier... usually a series of three (or 4) decent sized soldered joints.
You need to solder a tail onto one of these and lead it carefully out of the alternator for your tacho.
Don't use supacheap shit wire, these things get pretty warm. Ideally you want some nice flexible wire with woven high temp sleeve (like the tail on a H3 spotlight globe) or use some heatshrink.
Just make sure it can't rub through, tie it with cable ties or some silicone where it comes out of the housing but don't block the vent holes too much.
You need a heavy soldering iron. 40watts won't cut it unless you're very good at using it.
Ideally you need the joint scraped bright and clean, wrap a couple laps of your signal wire around it, then with your iron hot and fresh puddle of solder on the face, apply heat and a little more solder to the joint. You only want it there for a few moments, enough to melt them together but not enough to make it run and drip... because drips into the stator can be a nightmare... and too much heat will see solder wick inside the wire that you need to remain flexible. (that's why solder is illegal on aeroplane wiring)
Hope that helps.
for when I'm not driving the car of the century...
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