Tach problems

[Sledhead60]

I have tried three different tachometers on my 79 Invader and none of them work. Two were known to be good. (Supposedly) All wiring looks to be intact. Anyone have this same problem? Where do I start in locating the problem. I'm not really too good with wiring on a sled.

[Interceptor398]

What is the tack doing or not doing?

[rminier]

 The tach gets its signal from the lighting coil.
 One part of the sleds wiring harness should be constantly "hot" whenever the engine is running....that is the circuit to the brake light and the tach.
 Obviously, the brake light has to work with the key switch in the "on" position, or the "on/lights" position.
 Is your brake light working properly with the key in either position?...if not, you may have to check the wiring underneath the seat....it may be worn through and shorting everything.
 Or, you are really unlucky and you have 3 bad tachs.   
 An electrical multimeter should show some AC Voltage at the plug for the tach with the engine running.
 If the brake light works, it has to be "dead" tachs, or a problem with the wires (or connections) to the tach.

[kawhead]

check the 5 spade engine connector

[sxrsist]

my tach bounces alot, is there a possible fix for that

[rminier]

 sxrsist, I don't know the answer for that. I know my original tach got steadily worse with the bouncing needle over the years.
 I have checked the wiring, the grounds, the connections, etc. several times.
 I picked up a parts Invader in 2010. I tried the tach from it, and it worked like a charm.
   Now, it is starting to have an occasional bounce... ...not too bad yet.
I wonder if I should try gently tearing into my original tach.
For some reason, I have a sneaking suspicion that there is probably some $2 part that you could get from Radio Shack that might be the "Fix"...or a spot has corroded somewhere inside the tach.
 

[sprocket]

Wire in a  resistor from Wahlracing.com they are gold in color what it does is takes out the extra voltage spikes to tame your tachometer