Later 911 2.7 tacho,, wiring info anyone,please Options

[porschetub]

My current tach is from memory a 72 911 one,looks nice but that's about it,the needle is unstable as rpm changes and not reading right.
I have a later tach which is from a 76 and has 8 pins on the back (only 3 used) can anyone tell me what pins 2,5 and 6 are for ?.
1 x purple black to engine loom,
1 x brown earth,
1 x red/black switched power.
I need to know which wire to which pin,thanks in advance

[ClayPerrine]

The factory 911/914-6 ignition circuit is a capacitance discharge ignition. The points are just a low voltage trigger. The tach connection is hooked to the points and that doesn't provide the required voltage to drive a stock tach. Porsche didn't redesign the tach innards when they went to the CD ignition, they just slapped a tin can "Tach amplifier" on the cars. So your tach wont' work correctly.

Unfortunately these are unavailable from Porsche any more. The concurs 911 guys pay big money for them when they can find them.

Fortunately, you can use an aftermarket aftermarket tach adapter such as this:

MSD Tach Adapter

The MSD box is a CD ignition that generates multiple sparks. So their tach amplifier works on a 911/914-6.

I have one in my car right now. I put it in when the "tach amplifier" died. Works perfectly. Too bad I don't need it any more. The new motor is Motronic.