My tach is always jumping wildly all over the place. 30% of the time when your just cruising with the same throttle input it gives a steady reading and at idle. When your revving or accelerating it will bounce all over the place. I know that by the sound of the engine I'm around 3500 RPM but the needle shoots up to 8000 and the buzzer sounds off.

This problem has been going on for a few weeks now, and although it doesn't affect the performance of the car, it is VERY annoying! Where should I begin to look? I figured first thing to do is find a cheap replacement dizzy. Are there any other grounds or anything in particular that go bad on this car?

The problem seems to have started when I installed my Autometer water temp gauge. Maybe I'll try taking it out to see if the ground I tapped into is a problem.

 

I had a similar issue when my dizzy cap and rotor were bad

 

It could be a grounding issue. However, I would try switching your two ignitors with each other. If you have a third one laying around, then just replace your trailing ignitor with it. The tach reads off of the trailing ignitor. When they go bad, they cause the tach to go nuts. It's happened with me a couple of times where my car would start to spit and stutter out of the blue. I swapped the two ignitors and sure enough, the car runs perfectly, but the tach goes crazy.

 

if you have the points distributor still, it needs points.

if you have the electronic one, maybe you have a flakey connection, or an ignitor failing, or a bad cap and rotor

 

I have points on the car right now. I have 2 extra electrics laying around though. Can I just install the electric dizzy and use all of the points wiring etc?

 

have a quick search, its pretty simple

you could also adjust/replace the points, but they do need regular attention

 

So pretty much I just need to find a pair of FB coils and wire it to the FB dizzy? I have the harness for the FB dizzy and two FB dizzies.

 

http://www.mazspeed.com/ignitionswap.htm

great walkthrough on points to electronic dizzy swap.

or get a MSD and direct fire...

 

the tach signal comes from the leading on 79 models.

 

Wow...I had no idea. Another small, yet significant difference between the SA and FB. I wonder why the switch was made?

 

no idea why, there are no preformance gains from switching to trailing.

 

Because the trailing only works part time for emission puposes, 79 model only.