Installed new coil, now the tach acts funny
Have you tried an MSD tach adapter? If you're interested, I have two different models new in the packages. PM me with your email & I'll get some pictures.
I'll PM you. I will say that I asked the MSD guy if he thought an adapter would help, and he was doubtful. When I called Autometer, they said their tach needs a square wave to read the signal properly. My best guess would be to obtain an oscilloscope to confirm the waveform. Does the adapter change the waveform? Because that may well be what I need.
The reluctor gap in the dist is not a player in tach operation. The reluctor gap of about 0.008" is reqd to fire the coil, & the coil generates the signal to operate the tach.
This is a most unusual problem, since the Mopar ign box is inductive ign, which most tachs should work with when correctly hooked up. The tach signal wire should go the coil [-] terminal, which in my old MP book is a black/yw wire.
After reading your reply, I double checked my wires going to the coil, and I've got a brown one going to the positive terminal, and a black/yellow going to negative.
At first, I connected the tach to the negative coil terminal as it was prior to changing coils, and when I noticed the tach starting to function strangely, I referenced the Autometer literature and found this:
"If you have a Mopar Orange or Chrome Box ignition system on your vehicle, rather than connecting the Green signal wire of your tachometer to the negative side of your ignition coil, instead locate the Gray wire running between the Ignition Box and the Distributor. Connect your tach's Green signal wire to this Gray wire for a proper engine RPM signal."
So I connected it to that gray signal wire like they said, same problem. I thought I had fried the tach, so I bought a new one and I had the same behavior.
I'm not normally someone to give up on something, but I'm starting to question whether I even need a tach in the first place. The Scamp is anything but a race car....