Tacho (not idle) fluctuating

[adam.]

Gday all,

 

Hope you guys could give me an idea into what could be happening.

 

Bit of background, I have a '73 240z running an L28 with a 280zx electronic distributor, MSD 6A ignition, stock tacho with MSD tacho adaptor/booster.

 

My issue is the tacho fluctuates with every indicator flash, drops dramatically when the headlights are on (relays installed) or if my heater blower is on.

 

Note, driving/revving does not change, purely a tacho reading issue.

 

I have just bought a new battery and had a 280zx internally regulated alternator installed about two years ago.

 

Any ideas what is causing this fluctuation? It's bloody annoying!

 

It's getting to the point where it just hovers around the 1krpm mark all the time now.

 

 

Cheers,

Adam