Alternator driven Tach install

[bvanetten]

Guys, Did a search and didn't find exactly what I was looking for. I just bought a electronic tach that will run off of a crank trigger, an AC generator, an ignition coil, or an alternator. I plan of running off of the alternator. The instructions tell me to hook up one of the wires to the "W" terminal on the alternator. Which one is that? I see 3 connections on the back of the alternator. One big one on the bottom of the alt and two smaller ones that are part of a "box" that bolts to the passenger side of the alt. The big wire must be for charging so which one of the two smaller ones is the correct one? Or maybe neither of them are and I need to dig into the alt? Any advice would be helpful. I need to pull a car home tomorrow morning and I don't like to pull without a working tach.



Thanks,

Bruce

 

[JLEONARD]

Bruce,

Some alternators (not ours) have an "R" terminal.

What you need to do is remove the alternator so you can remove the rear sheetmetal cover. Once inside you'll see several rectifyer lead connections. Simply loosen/remove one of the screws and attach a small wire (I used one side of a speaker wire) with a ring connector. You may have to provide some clearance to one of the slots in the cover to get the wire thru without chafing.

Once everything is wired up, you will have to calibrate the tach with a hand held optical tach.

Jay

 

[bvanetten]

Jay, That's the info I needed. I found several sites that refered to this. Something about taping into the stator side of the alternator to get a pulse. Their are 4 leads under the cover, I'll tap into one of them. As far as adjusting, there is a formula used to determine how many pulses per revolution your alternator puts out. First you need to get your pully ratio. Your pulley ratio is the crank pully diameter divided by the alternator pulley diameter. Pulses per revolution is (the # of poles in the alt divided by 2) X the pulley ratio. With this # you turn on dip switches on the tach to equal that #. I'm almost sure our alternators are 12 pole. I'll let ya know how it all turns out. BTW I bought a GBI Precision programable tach from a big rig parts house called Fleetpride. It is a 3 3/8th inch gauge that goes to 4K rpm and has a built in digital hour meter. It will run off of an alt, generator, ingnition, or crank trigger signal. Best of all it was about $110 out the door. Looks good and matches my classic autometer speedo.



Bruce

 

[JLEONARD]

Bruce, good glad you got it going.

I know there's a formula, and it gets you in the ballpark, but a few minutes with an optical tach will get it darned near perfect.

Jay

 

[CumminsKid]

part #

What is the brand and part#? Autometer?

 

[bvanetten]

http://www.gbinstruments.com/ is the manufacture. I forget the part#. BTW I wasn't able to get it working yesterday. I called GBI this morning and told them what I was trying to do. They told me that I needed to take the alt to a rebuilder and have them wire it up with a "W" terminal or wire out of the back. I wish I knew exactly what a "W" terminal was. More importantly I wish I had a wiring diagram of our alternators and instructions on how to wire it up properly. This can't be that difficult. I really like the look of the gauge. Matches my Autometer speedo almost exactly.