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Old 11-30-2007, 02:42 PM   #1 (permalink)
rtarh2o
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Alternator lead for tach?

I am doing a 6.2 conversion in my 94 Toyota Land Cruiser and was told that there is a lead on the back of the alternator for the tach? I bought a new alternator and don't have any of the engine wiring so just need to know what to look for on the alternator?
Rusty
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Old 11-30-2007, 04:58 PM   #2 (permalink)
0lee
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The terminal a tachometer can be connected to is usually called "W terminal". Most alternators don't have that, and if you can find one with that terminal that goes on a 6.2, I can imagine a number of people might be interested in that. Even if you can't find one with a W terminal, you usually can modify the alternator (internally) to get that terminal. In any case, you need a tachometer which recieves the speed signal from the W terminal.

An alternative is an Autometer 2888 tachometer. It comes with a magnetic coupling that needs to be installed on the alternator to provide signals to the tachometer. After installation, this tachometer needs to be calibrated to actual engine speed to provide accurate readings.
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Last edited by 0lee; 11-30-2007 at 04:59 PM.
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Old 11-30-2007, 05:52 PM   #3 (permalink)
Earl87gta
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go to dakota digital gauges web site and they have Universal Diesel Tachometer Adaptor.
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Old 12-02-2007, 07:53 PM   #4 (permalink)
eppoh
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Ir you want RPM for jsut troubleshooting or occassional reference, don't spend the money on any tachometer systems.

If you have a laptop or Pocket PC like a Dell or HP handheld, you can download a free program called RPM from sound. http://tunelab-world.com/rpmsound.html

It works on any internal combustion engine and is accurate to about 1 rpm. I have used it on a light plane to check the accuracy of the mechanical tach. Works great.
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Old 12-02-2007, 08:04 PM   #5 (permalink)
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Quote:
Originally Posted by 0lee View Post
The terminal a tachometer can be connected to is usually called "W terminal". Most alternators don't have that, and if you can find one with that terminal that goes on a 6.2, I can imagine a number of people might be interested in that.
That "W" often found on Bosch alternators on Volkswagen diesels is just a stator tap. You can to the same with any alternator. If you buy an aftermarket diesel tachometer, it will come with instructions on where to tap into the alternator stator.
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Old 12-02-2007, 08:54 PM   #6 (permalink)
jdemaris
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Quote:
Originally Posted by rtarh2o View Post
I am doing a 6.2 conversion in my 94 Toyota Land Cruiser and was told that there is a lead on the back of the alternator for the tach? I bought a new alternator and don't have any of the engine wiring so just need to know what to look for on the alternator?
Rusty
The older Delco 10SIs or 12SIs don't have a tach lead - you have to install it your self by tapping into the diode-trio.

The newer Delco CS alternators do have a tachometer lead - it's terminal "P." On other makes e.g. Bosch or Hitachi, it can be S, T, or W.

Some tach kits give instructions on how and where to tap the alternator stator.

Other kits - like Auto Meter 2888 provide an external inductive stator pickup that mounts on the back of the alternator.

Stewart Warner diesel tachs need some sort of pickup component that creates a signal from a turning shaft.

Some 6.2 and 6.5s have a pickup mounted on top of the vacuum pump - usually just early 90s trucks.
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1982 K10 PU 6.2 diesel,1983 (two) Blazers 6.2 diesel, TH400, 1983 K5 Blazer with 6.2 diesel, 4sp man. OD trans. and Chalet pop-up camper body.
1986 K5 Blazer 6.2 diesel, 700R4 trans.- with Halmark pop-up camper body.
1987 V20 4WD Suburban 6.2 diesel, 1988 K5 Blazer 6.2 diesel, 700R4. 1989 GMC 3/4 ton, 4WD Suburban, 6.2 diesel, TH400 trans.
1991 Suburban 4WD 6.2 diesel 700R4 trans.
1981 (two of them) Chevy Chevette with 1.8 diesel and 5 sp. trans.
1985 Isuzu P'UP 4WD pickup with 2.2 diesel
1991 (Two of them) Volkswagen Jetta 1.6 diesel
1985 Ford F250 4WD ex-cab, longbed, 6.9 diesel
1994 Ford F250 4WD ex-cab, longbed, 7.3 IDI turbodiesel.
1983 Mercedes 300D five-cylinder turbo-diesel
1992 Dodge D200 4WD Cummins turbo-diesel, intercooled with 5 spd Gertrag
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Old 12-02-2007, 11:20 PM   #7 (permalink)
rtarh2o
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I found this picture online and it turns out it is the same alternater I have. There is a tab that is identified as the tach lead, is this correct?
Rusty
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Old 12-03-2007, 02:17 AM   #8 (permalink)
pontiac59
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Not to hijack, but will that lead work with any of your typical aftermarket tachs? I have a Sun Mini kicking around I never put on the gas truck - it's small enough I think I can fit it in one of the left side gauge pods.
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Old 12-03-2007, 08:50 AM   #9 (permalink)
jdemaris
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Quote:
Originally Posted by rtarh2o View Post
I found this picture online and it turns out it is the same alternater I have. There is a tab that is identified as the tach lead, is this correct?
Rusty
That looks like a Delco 10SI or 12SI with an installed stator-tap -which connects a wire to one of the three leads of the internal diode-trio. It made to work with a certain tachometer - not all.

You have to match the tach to the type of signal being used. Gas engine tachs made to work off an igntion signal will not work.
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1982 K10 PU 6.2 diesel,1983 (two) Blazers 6.2 diesel, TH400, 1983 K5 Blazer with 6.2 diesel, 4sp man. OD trans. and Chalet pop-up camper body.
1986 K5 Blazer 6.2 diesel, 700R4 trans.- with Halmark pop-up camper body.
1987 V20 4WD Suburban 6.2 diesel, 1988 K5 Blazer 6.2 diesel, 700R4. 1989 GMC 3/4 ton, 4WD Suburban, 6.2 diesel, TH400 trans.
1991 Suburban 4WD 6.2 diesel 700R4 trans.
1981 (two of them) Chevy Chevette with 1.8 diesel and 5 sp. trans.
1985 Isuzu P'UP 4WD pickup with 2.2 diesel
1991 (Two of them) Volkswagen Jetta 1.6 diesel
1985 Ford F250 4WD ex-cab, longbed, 6.9 diesel
1994 Ford F250 4WD ex-cab, longbed, 7.3 IDI turbodiesel.
1983 Mercedes 300D five-cylinder turbo-diesel
1992 Dodge D200 4WD Cummins turbo-diesel, intercooled with 5 spd Gertrag
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Old 12-03-2007, 09:46 AM   #10 (permalink)
0lee
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Quote:
Originally Posted by pontiac59 View Post
Not to hijack, but will that lead work with any of your typical aftermarket tachs? I have a Sun Mini kicking around I never put on the gas truck - it's small enough I think I can fit it in one of the left side gauge pods.
If it's for a gasser, it won't work unless it's designed to get the signal from the alternator (which seems unlikely).
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