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914World.com _ 914World Garage _ Black/purple Tach Wire..question

Posted by: DougC Nov 28 2005, 04:55 PM

The Black/Purple wire usually (4 cyl stock) goes to the "-" side of the coil, right? So I have my MSD unit hooked up and the car (6 cyl, MSD) idles and runs fine but the tachometer isn't working.. actually the blk/pur wire isn't hooked up right now either. So, I have a tach adapter and I'm assuming that the "-" wire from it will go to the neg side of the coil with the blk/pur wire from the harness. Does that sound logical? I've researched this quite a bit today so any insite would be appreciated.

Doug C

Posted by: TimT Nov 28 2005, 05:22 PM

what year is the car?

some VDO tachs (early ones) dont work without the MSD Tach-Adapter

Posted by: Joe Ricard Nov 28 2005, 05:41 PM

The black purple wire is the signal wire for the tach.
On my Mallory 6A box there is a tach output wire. Wouldn't work with the early tach so I went with an Autometer 5" REALLY NICE. Fit right in the hole too.

Posted by: Porsche Rescue Nov 28 2005, 07:30 PM

I too have an Autometer wired from the MSD tach output using the black purple wire (with MSD you connect NOTHING to the coil other than the two wires from the MSD).
Not sure where an adapter plugs in but use the black/purple to get from the engine compartment to the dashboard.

Posted by: TimT Nov 28 2005, 07:56 PM

oops misread the post

yes tach out from MSD goes to black/purple, this signal may have to be conditions by the tach adapter, depending on the year of the vehicle...

Posted by: Aaron Cox Nov 28 2005, 10:19 PM

i did the same thing......

here is what you ned to do. tach mod, or get a tach adapter.....
jumper the initial signal resistor inside the tach...

black wire in center of picture....

Posted by: DougC Nov 29 2005, 09:50 AM

What picture aaron?

OK, I have the tach adapter..although there are no markings on it, I've been told that's what it is. One wire is lable "-" and the other is "+" so how does it hook into the system? BTW, the car is a '73 .

here's the adapter I have : http://www.914world.com/bbs2/index.php?act=ST&f=2&t=38847&hl=

Doug C

Posted by: Mike D. Nov 29 2005, 01:57 PM

Doug, Don't take the tach adapter out of the package, return it, it wont work. I just went through the same thing. 4 cyl. tach would run off the MSD plug but of course was totaly inaccurate. Then I went a got an early 911 tach and got nothing, bought the tach adapter, and still nothing. ended up taking the tach to North Hollywood speedo and getting them to convert for use with MSD. The Guy there said they completely replace the board inside with one they make just for MSD.

Took it home, plugged it in, works perfect.

Is your car a 2.0 with webbers?

Posted by: DougC Nov 29 2005, 02:14 PM

No Mike, it's a 2.7L six with CSI ... I am using a 911 Tach - I believe. Well the tach worked for the previous owner of the 914 that was powered by this engine...but then he wasn't using MSD just a stock CD box.

Doug C

Posted by: Porsche Rescue Nov 29 2005, 02:19 PM

Won't hurt anything to try the 911 tach. Connect the black/purple to the msd tach output and the other end to the tach input. Make sure other wires required are connected to the tach as well.
If it won't work, call MSD about an adapter.

Posted by: Aaron Cox Nov 29 2005, 04:53 PM

QUOTE (DougC @ Nov 29 2005, 08:50 AM)
What picture aaron?

OK, I have the tach adapter..although there are no markings on it, I've been told that's what it is. One wire is lable "-" and the other is "+" so how does it hook into the system? BTW, the car is a '73 .

here's the adapter I have : http://www.914world.com/bbs2/index.php?act=ST&f=2&t=38847&hl=

Doug C

tach mod for CDI box...
user posted image

jump initial signal resistor....

late model tachs have this done already....

74+ tachs should work fine.

what year is your tach? snap a pic.