Tach question

[allsierra123]

My alternator doesnt seem to have a W terminal where it should be. It has a D+ and a D- any idea what those are for is one for the tach? Im trying to get my dakota signal converter setup.

[Rabbit on Roids]

if it doesnt have a w terminal in the w spot, then it probably will not drive a tach.

[allsierra123]

ok well the part number seems to corrispond with the late model TDI. I mistyped its DW and D-.  So no bones on working with a tach? I have a gasser tach if that makes a difference.

[Vincent Waldon]

It has a D+ and a D- any idea what those are for is one for the tach?.

Yeah, unfortunately the answer is "neither"... to drive your Dakota tach set up you're going to need the W signal.  TDI's get their tach signal from the ECU.

If you don't mind disassembling your alternator it's actually pretty easy to add your own... you just add a wire pre- diode bridge:

[allsierra123]

good to know. Wonder what those terminals are for on that alternator then.

[allsierra123]

Why wouldnt it drive it. Thats what they sold it to do. If it doesnt I am going to be returning it. They said converts the w signal to a gas tach signal.

[blackdogvan]

Here's my experience with the dakota Digital w terminal converters.
I bought one for my 1986 westy when I first started messing around with the aaz conversion, worked right off the bat for 5 years (this was the old model with all the dip switches). When I swapped the motor into a 1991 van, it no worky. So i figured the DD box bit it & bought the new model. It didn't work either. So yesterday I swapped the tach module out of the 1986 westy into my 1991 GL & TADAAA it works. To make it more confusing a while back I sold the old box that I figure still works just fine to a friend with a 1985 Westy AAZ combo & it doesn't work for him now, but it may be a dip switch thing. I read somewhere that the later model tachs aren't as sensitive as the earlier ones.

So my answer to the DD box & a Vanagon tach is... maybe.
Swapping out the Tach module is pretty easy, took 1hr to re & re both vans. You just pop out the gauge cluster, un-nut the fuel & temp, unplug the tach connector & peel back the flexable circuit. I rate it a 2/10 for difficulty.

[allsierra123]

Good to know. MIne has dip switches still. If I have to swap out for an older tach I dont mind. After everything else I have done to the van swapping a tach is not a big deal.

[blackdogvan]

Do you have the instructions? We can't find them so the correct dip switch locations would be really helpful!

[allsierra123]

yeah I actually do.

[blackdogvan]

Cool, if you (or anyone who has the older DD box) could post the correct dip switch positions for our application that would be great!

[Sam Johnson]

All,

Last year I installed a 1.9 TD in my 1988 Vanagon.  Of course I had the usual tach problem as my gas tach would not work with my diesel engine.  However, I did have the W terminal on my alternator.   

After reading about the Dakota Digital box that seemed to be the way to go.  Unfortunately, it did not work, no matter what switch setttings.  Therefore, I sent it back.

Plan B was to follow the long discussion and change the resistors and capacitors on the circuit board.  My neighbor works as an engineer for IBM and does work like this all the time as they design cicuits.  No matter, this approach also did not work--it just pegged the needle as soon as it was connected to the + and - lines. 

Plan C I contacted Dakota Digital and we agreed I would send my tach and they would use it to determine why the DD box does not work with the Vanagon tach.   After about three months, they sent it back as the tech that had been working on this question left and they did not have staff or motivation to really discover the answer.

Finally, I saw an ad on the For Sale section and purchased a diesel cluster (from a MKII I think) out of Canada.  The tach fit right in my Vanagon cluster but it registered two times what it should.  I played around with the adjustment screw but was uncertain which way to turn it.   About that time there was a discussion that talks about this problem and the need to change a resistor.  Once burned I was not that excited about messing with the circuit board.  Finally I found a discussion that said to turn the screw counterclockwise and, wallah, it now works spot on.

Not certain if this helps but at least it shows you may have to keep on trying various options before you find one that works for you.

Regards,  Sam
Tucson, AZ

[blackdogvan]

Dakota is now advertising they their units are ok for pre 1986 gauge clusters...

[Smokey Eddy]

You can just open up the alternator and solder on a wire to any of the three stator coils; that will give you the "W" signal.  Unfortunately, I don't think your Dakota Digital will drive your gasser tach; at least mine doesn't.  I've solved this problem by building my own driver so I could run the gasser tach as well as the dynamic oil pressure warning system, which takes a tach signal for input (I have a converted Vanagon).

I ran the Dakota & homebrew driver for a year or so and it worked great.  I've recently replaced the Dakota unit with my own design which has the driver built in.  It's easier to adjust too; a 20-turn trim pot instead of those up/down pushbuttons.

PM me if you'd like more info on the converter or just the driver board ...

please please please pm me with any documentation of this!! I've been trying so hard and i can never get those FLIPPING chips to work properly consistantly.
please PM ME!!

[allsierra123]

Yeah same here are you producing them or can you give the info. Im interested either way,