I'm nearing the final stages of a Buick V6 swap into my 914. I am using an MSD billet distributor and MSD 6200A ignition box. As best I can tell from the Haines wiring diagram, the 914 12 pin harness wire, black wire with purple stripe that normally connects to the negative side of the coil, is the tach signal wire. I am guessing that the black/purple wire would be the one to connect to the MSD box tach output signal connection. Can anyone correct me on this if I am wrong in my guess?

Thanks,
Don

Yes the Black and Purple Wire is the Tach wire. In some cases you may
need and MSD convertor box for the Tach to work.

let me know when/if you get the tach to work.

even with the right adapter, i could not get my tach to work at all ...
Andy

Thanks Joe! I'll see how it goes in a couple of days when I hope to fire it up for the first time. I'm waiting on a new steering shaft bearing so I can put the steering column back together after installing a new key switch. The bearing should be here tomorrow.

Sir Andy,

That is not encouraging news. But then again, it would give me an excuse to go buy one of those big racey looking Auto Meter tachs.

QUOTE (SirAndy @ Sep 26 2005, 02:16 PM)

let me know when/if you get the tach to work. even with the right adapter, i could not get my tach to work at all ... Andy

Andy,

No adapter required. I plugged the black/purple wire into the MSD box tach signal and my original 914 tach works fine. I fired the Buick V6 engine off for the first time last Friday, no problems.

QUOTE (dbledsoe @ Oct 3 2005, 02:55 PM)

No adapter required. I plugged the black/purple wire into the MSD box tach signal and my original 914 tach works fine.

well, what the hell ????

i got a MSD box and dizzy and i can't get my /4 tach to work at all ...
Andy

Andy, how are you wiring up the adapter?

early silver button or late button tach andy?

it makes a HUGE difference...

QUOTE (jkeyzer @ Oct 3 2005, 03:15 PM)

Andy, how are you wiring up the adapter?

according to the instructions that came with it ...

Andy

QUOTE (Aaron Cox @ Oct 3 2005, 03:32 PM)

early silver button or late button tach andy? it makes a HUGE difference...

aha, now we're getting somewhere ...

silver button it is ...
Andy

mallory boxes have same problem with early tachs.

find my thread. 'hyfire tach mod'

you have to jumper the initial signal resistor
no adapter required then

I have a silver button tach, it works.

I think the most common mistake people make is that they put the adapter in series with the tach wire instead of in parallel.

QUOTE (jkeyzer @ Oct 3 2005, 04:21 PM)

I have a silver button tach, it works. I think the most common mistake people make is that they put the adapter in series with the tach wire instead of in parallel.

well. it ain't working without the adapter (read, putting the wire directly into the box) and it ain't working with the adapter, hooked up according to the instructions that came with it.

and yes, i know how to read instructions, thanks for asking ...
Andy

The early and late tachs take different signals. I'm not sure the switch was exactly when they went from silver button to no-button. The late tachs are happy with a simple square wave of well under 12v (even 5v might work). The early tachs need the ringy, spikey (up to 30v) signal straight off a coil to work. The primary difference appears to be a single resistor inside the tach, the early ones having one to limit the spike currents, the later ones lacking this resistor. There are detailed photos on this site of the tach guts and exactly what you need to do to do the conversion.

Once this is done, no adapter box should be required, and the late style will still work straight off the coil (w/o a CDI box).

QUOTE (lapuwali @ Oct 3 2005, 04:37 PM)

The early and late tachs take different signals. I'm not sure the switch was exactly when they went from silver button to no-button. The late tachs are happy with a simple square wave of well under 12v (even 5v might work). The early tachs need the ringy, spikey (up to 30v) signal straight off a coil to work. The primary difference appears to be a single resistor inside the tach, the early ones having one to limit the spike currents, the later ones lacking this resistor. There are detailed photos on this site of the tach guts and exactly what you need to do to do the conversion. Once this is done, no adapter box should be required, and the late style will still work straight off the coil (w/o a CDI box).

tachs changed late 73...early 74 to black button

Here's the thread:

Tach mods

I'm not convinced there's a 100% correlation between the finish on the center button and the tach input circuitry. Did the '74 tachs also have a single turn signal light and the high-beam light at the top rather than the bottom of the face?

QUOTE (lapuwali @ Oct 3 2005, 04:43 PM)

Here's the thread: Tach mods I'm not convinced there's a 100% correlation between the finish on the center button and the tach input circuitry. Did the '74 tachs also have a single turn signal light and the high-beam light at the top rather than the bottom of the face?

74 MY had single directional blinker. MY 73 and earlier had 2. this is also the change to black buttons...

Another tach mod thread

Andy,

An update:

The tach works fine but I think it is not accurate. With the original carb'd 98mm bore type IV engine I ran just below 3k rpm at 60mph. I took the Buick V6 conversion out for its first run on the road and found, according to the tach/speedo, I was running 3.5k at 60mph, which I don't believe is correct. Idle was at 1k rpm after warming the engine, which is high for a basically stock Buick V6, and it was barely idling (closer to wanting to die). That tells me the signal isn't what it should be. A Buick V6 should idle easily at 7 to 8 hundred rpm (someone feel free to correct me if I'm wrong on that).

Cool! I'll get to order that nice looking Auto Meter tach I have been coveting.