Tachometer

When the electric connection on a 86 fails, does the tach peg on wide open?

Which electric connection?

If the power to the tach fails it sits on 0.  If the input to it fails it sits on 0.

never heard of that one. is it pegged whether the engine is running or not? power on or not?

From personal experience, it will peg on a bad ground.

That is good to know, Chris.  Thanks!

No problem.  I've never followed it back from the battery to the tach, but on my battery there is a ground wire apart with a ring connector apart from the main connector that goes over the negative post on the battery.  

The screw that tightens down the negative battery cable onto the post has a through hole for a bolt to go through the connector, and a nut to tighten the connection.  On my truck, this extra ground slips over the bolt after it passes through the main connector and before the nut that normally tightens the main connector down.

In my case, I didn't tighten the nut down (it was loose) causing a intermittent connection of this additional ground to the main negative terminal connector.  Once I tightened the nut, the ring terminal connector for this extra ground was nice and tight against the main cable connector that goes over the battery post, and all was well.

It is the tach. Pegged at wide open. I will check the ground tomorrow. Thanks.