tach question gasser vs diesel

[92EcoDiesel Jetta]

vw gasser tachs run off the ign coil. vw idi diesel tachs run off the alt W terminal. What is the frequency of the tach signal (relative to crank) of the ignition coil and the alt W terminal output?

[RabbitJockey]

someone had theirs on an oscilloscope, you'll have to search

[92EcoDiesel Jetta]

I hooked up a MK1 gasser tach to the W terminal  of my 92 Eco alt. Had to rev the engine before the tach would register and then it would read 3000 rpm at an idle of 1000 rpm. I won't pursue running the tach on the alternator (on my Caddy) any further and stay with a mag pickup and trigger.

[92EcoDiesel Jetta]

vw gasser tachs run off the ign coil. vw idi diesel tachs run off the alt W terminal. What is the frequency of the tach signal (relative to crank) of the ignition coil and the alt W terminal output?

Based on my post above and what little else I know, I am going to answer my own question.

The ignition coil signal is 2 x crank speed. The W terminal signal is 6 x crank speed.

[Gizmoman]

I slipped one of these (Tiny Tach) into my dash on an 82 Vanagon with an AAZ. Ran a wire from #1 injector line (from the included clamp) - sweet and simple, no mucking around.
It's got a soft green glow and is easy to see. It's also an hour meter as well and keeps track of max RPMs if you care.
http://www.amazon.com/Tiny-Tach-Hour-Meter-TT2A/dp/B0045L9GA0/ref=sr_1_1?ie=UTF8&qid=1353374191&sr=8-1&keywords=tiny+tach.

[92EcoDiesel Jetta]

Thanks. I know about the tiny tach. I personally do not like digital tachs and prefer an analog one.

[Gizmoman]

Gotcha on that - I wonder if there is an analog tach that works of the same "pulse" signal from the injector line?

[92EcoDiesel Jetta]

Gotcha on that - I wonder if there is an analog tach that works of the same "pulse" signal from the injector line?

Probably. Technically it is not difficult to do, just more expensive since a meter movement is needed. Then you have to find a spot and custom mount it. For me, I prefer an OEM looking analog tach in the instrument cluster.