Plugged in another tach, no good
 

Here I am with an aching ass shoulder and I decide to change out my tach that I pressumably fried while welding on the muffler a while back.

The second tach doesn't work. Now, I'm not one to send it off to N. Hollywood speedo until I know that something else could not be causing this.

Ideas?

Oh, and if you don't answer me in 5 minutes, I'm gonna be "disappointed in the forum." ;) :D

Zeke,

Well, you could check for ground pulses at the tach input wire as you turn over the engine ... if they don't make it that far, there's the forward 14-pin connector and a couple of other stops meandering through the relay panel wiring to the CDI and Speed Switch. Those crimps are only 34-years old, you know!

Thank you sir. While you were answering, I was out in the car with the meter on the black/purple wire getting variable voltage with the rpm change. I guess both my tachs are dead. I've got one completely disassembled down to the electronic chassis and that's where my knowledge stops. No physical damage visable. All those diodes and whatnots keep their little secrets from guys like me.

What is the pisser about this is that I have the whole steering wheel, hub and covers off in order to get the tach out. I'm gonna have to do this twice!

Don't feel bad zeke, even EE like me needs a schematic to troubleshoot what the hell is wrong.

I woudl try to aligator clip a jumper directly from battery ground to tach ground. Same with the positive if it applies (dont have wiring diagram in front of me). Then try both the tachs. ps do they work in another car?

Thanks for the help in the past.

Good ideas there. I did all that. Don't have another 911 to swap instruments. Maybe that's what wrong. :D

I already put a dead tach back in and put the wheel back on resigning myself to a $125 charge to find a resistor or diode and solder it in. I need the turn signal lights and don't want to look at a hole. You know how us old guys like to drive down the freeway with the blinker going.

I'm just gonna wait for the first jerk that says, "That's not a real S, it doesn't have the 7300 rpm tachometer."

I know one thing, I have a lot more welding to do and the refurbished tach is not going back in the car until that's all done. So, I'm tachless. I guess that's better than being tacky. ;)