Modern tacho alternator driven

Bought a $89.00 tacho that is alternator driven , nice looking, the only thing wrong is I cannot get it to work, apparently 1 wire connects to a "”letter w “” or “”l “” or a favourite Chinese saying..... connection to ecm or cpu , if I’d paid $25 I could understand plus it oddly looks very good quality, as it turns out I don’t have a letter l or w and no ecu ..... I tried hooked it up on the old negative side of the coil , bad move , the truck wouldn’t even start , no damage apart from the almost $100 almost paperweight , mate or mine who dabbles in mechanical misfits as we all do , told him of my underwhelming adventure and he laughed and said as long as we don’t mind a nottcy digital 2” coil type it’s yours for free , I couldn’t run quick enough lol ,, so I went from a 90mm nothing to 50mm notchey tacho life is good, and luckily I kept the original 90mm gauge with nothing that works, but I can deal with that, now can anyone please tell me what “”. L. “”” or “”””W. “ can I use without cooking the alternator , pretty please thanks , picture of informuos tacho the alternator is new in the box bought before the tacho, it is I think a npr Isuzu with a vacuum pump, going on the acco as there’s enough pipes to take it to the moon and back, I also bought a vacuum gauge so I know if it’s running on atmospheric air or a actual vacuum for the engine and 6 million other vacuum hoses, tanks , brakes etc , I’m sure I’ve missed something but I think u get the message....
Im not sure if a tacho can be fitted, maybe I have to bite the bullet and call a elec when the alternator and pump is plumbed for oil

Presume the "I" might be ignition. Still searching for "W".

S terminal - Senses battery voltage
IG terminal - Ignition switch that turns the voltage regulator on
L terminal - Closes the circuit to the warning lamp
B terminal - Main alternator output terminal (connected to the battery)
F terminal - Full-field bypass for regulator

You need an unrectified output on the alternator to connect the tach to. I suspect the alternator you have does not have that output as the tach in an isuzu is probably run from the ECU.

Thanks guys, I’ve got a working 2” led tacho one for now and A paper weight to fill up the hole and I’ve got 6 2” gauges too fit sensors and got to fit some sort of rear bumper, I’ve fitted normal plastic mudguards and being so high I’m not sure what to do for tail lights and bumper

Had the same problem and had to get an auto electrician to dismantle alternator and solder a wire direct into something inside alternator

Google "adding W terminal" should get you some reading.
Appears to be just adding a wire to one of the stator windings before the diode
Cheers Steve

Cliffo what type of alternator and would it been cheaper to buy a alt/tach that worked from day 1 , ive spent $300 including tacho so wondering how to get around it.... Jim

Hi Rattaill. In your first lot of pics the 3rd down shows a pic of 3 terminals, 2 running the same direction and the 3rd at right angles. The one at right angles shows the letter "L" next to it but in the diagram below it is identified not as the "L" no wonder these things cause headaches.

Cobba

I think the "L" is referring to the correct pin not the right angle one. Many of these terminals have their markings poorly positioned leading to ambiguity.

Lang

When I fitted Detroit into Diamond T I needed vacuum as the truck had vacuum booster so fitted alternator with vacuum pump and ran electronic rev counter and as I said I had to get auto electrician to solder extra wire into windings to operate rev counter and it works ok