Mercedes Om617 with tachometer(fix?) Using alternator.

Joined
Oct 13, 2018
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4
Location
Michigan
I had a heck of a time finding any information on this subject. I'm doing an om617 swap and am using the Dakota digital dsl-1e unit. In order to get a signal from the alternator you need a "w" connection, well the stock Benz alternator and the Saab 900 alternator don't have one stock so you need to make your own. This is kinda a how to, but really just putting the info out there to help anyone else who needs it.

You got to install a "w" wire to get the reading for the Dakota digital. From what I gather the wire is a connected straight to one of the windings before regulator (uninterrupted a.c. current) so I soldered a wire to the winding. Ran the wire out a hole in the back of the casing. Put a vacuum hose around it to keep it from chafing. And connected it into the Dakota digital unit.

I say fix? Because the unit is getting a signal and my tachometer moves but i have yet to get it calibrated correctly to the point of accuracy. If I get it working I'll update this post. And if I can't get it I'll delete it. Anyone want to correct me on it and I'll learn something.

My truck is a 1986 4runner with the turbo gauge cluster (analog)

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Joined
Oct 13, 2018
Messages
4
Location
Michigan
Update: it works. I can't believe it took me so long to get it right, my issue was wiring the Dakota digital, having to jump the "none used" position with the "high power" position. So confirmed way to make a om617 work with the stock sr5 gauges with 22re.

The rats nest is all cleaned up now

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Joined
Apr 21, 2004
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266
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Bainbridge Island
Can you please show how the Dakota is hooked up to the OEM wiring? I'm almost finished with the exact same swap, and am about ready to dive into this. I have removed all of the un needed wiring from under the hood. IE distributor, Injector wiring, etc.
 
Joined
Oct 13, 2018
Messages
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Location
Michigan
Rainy day fzj. I didn't use any of the truck wiring to make the tach work. I made and ran each individual wire for the swap.

To find out what position is the "tachometer" on the 3 connectors on the back of your dash, just look in the fsm or find it on a another thread.

The best I can do is show you a picture of a drawing. I made.
The hardest wire to make is the "w" signal wire from the alternator like I showed above.
The rest just run them from wherever you can get a 12v and ground the easyiest

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george_tlc

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Joined
Sep 17, 2003
Messages
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Sunnyvale, CA
Yep, W wire goes to any of the windings "pre-diode". What you get is essentially raw AC and frequency will be (number of poles in your alternator: the big lumpy metal looking things) x pulley_ratio x rpm. Obviously the tacho you are using needs to be able to take the AC signal and also allow you to set the # poles and the pulley ratio so you can get actual engine RPM.

6 poles is pretty common on alternators (at least the older variety).

e.g. poles looks like -> How An Automotive Alternator Works. and each 'pole' is a N/S pair. So you'll see 6 north and 6 south on a 6 pole alternator.

cheers,
george.
 
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