Continuing Tach Issues

One of the first and easiest things to check is to remove the tach sensing wire at the coil, lightly sand the terminal down to bare metal (with emory cloth or similar), and reconnect.

The radio sounds like maybe a loose ground, which could also be causing the tach problem, but if it doesn't quit in synch with the tach failing, it's probably unrelated.

^^This^^

I took a long piece of wire and connected it from the coil to the tach (removing the original wire). That did not fix it.

I then hooked the wire up to the other side of the coil, thinking maybe they had put the tach coil wires on the wrong side. That did not fix it. 

I then use that wire to connect the tach ground girectly to the battery ground. That did not fix it.

The tach only has three wires: switched power, a ground and the wire that runs to the coil.  Seems pretty simple.

I have used a separate wire to bypass the car wiring and check the ground and the tach signal. 

Since I tested two of the three wires going to the tachometer, I thought I would try the third one. I hope they voltmeter up to the switched power and the ground and measure voltage.

It varied quite a bit, is this normal? 

Voltage drops did not correlate to the tach going to zero however. 

Do you have the old OEM stye VW ceramic fuses? They do get corrected at the ends over time.  Points or Pertronics "points"?

I have modern fuses and "real" points.

Yes, the fluctuations in what should be a steady DC voltage do seem weird.

Do you see the same type of fluctuation at other points that should be steady DC (like the hot feeds to your radio or headlights?

If so, recheck the main connections at the battery (positive and negative). Remove cables, sand connections to bare metal, reconnect. If the connection is dropping out and reconnecting for fractions of a second, some circuits may not show obvious problems, but an electronic device like a tach would.

Semi-educated guessing here.

Cole.

You're issue is probably not what I struggled with in this thread, but it's worth a read to at least rule it out.

https://www.speedsterowners.co...5#560883158758755955

In your video, it looks like the arbor that the needle is mounted on is a little wonky.  It could be the vibration of the car while you were videoing the needle drop, but since you eliminated all the connection points, I would suspect the tach.  Do you have a spare tach or a test instrument to use in its place? 

  As an aside, I thought I had a horn issue as I was getting a voltage reading at the horn when the button was pressed.  I replaced the horn and no beep still. I ran a wire with alligator clips down to the horn and..... wait for it..... still no honk.  Now, I’m going a little batty right? So, I take the old horn, hook plus and minus to the battery and it works, the new horn works too when hooked temporarily to the batt.  So, I look at where I clipped the alligator connector for the temp wiring and the flipping crimped on spade connector was the issue.  I cut it off and used a modern, Klein brand crimping tool and now I get the full Hella BEEEEEEEEP!   In short, make sure you connect your temporary wires to the actual contact points. Good luck with your wiring! 

So far, you're getting two different devices cutting out in proximity to each other.

You've swapped out the Tach unit with a new one and see no change, so that would point to the sender/distributor.  You've run a dedicated wire from the disti to the tach - no change - so that should eliminate the sender signal line.  Points are binary (either on or off) but can become pitted and act erratically, so clean them up if you have a points burnishing tool or drop in a new set, just to eliminate that.  Points would NOT affect the radio, however.

The voltage excursions on your DVM bother me, though.  As Mitch said, it should vary around 14 volts but it should be a slow sine wave movement, not bouncing around (it would kind of bounce if you have the old-style voltage regulator, but you probably have an alternator with solid state voltage regulation so it should be smooth).  You're seeing instantaneous swings down to 7-8V for less than a second and then back up - that's not good.  It acts a lot like a dirty ground being affected by external things turning on and off and seeking a better ground reference through those devices.  

When the engine was replaced, did they mess with the ground strap from Transaxle to frame?  Find it (up near the nose of the transaxle and connecting to the frame) and clean it up.  

When they installed the alternator/fan shroud, did they install an insulator/spacer between the alternator and the pedestal?  Sometimes people put those on to lift it up and it doesn't ground properly.  If you have a hunk of 10 ga. wire, you could run it from the alternator case to the car's frame to see if that helps.  If so, look for a missing/loose ground strap, transaxle to frame.  

It sounds like your battery to frame ground connection is OK, but I would clean that, too, if you haven't already.  

That's all I have for now.  See what happens.  gn

Oooo... Wait......   This sounds stupid, but are all four of your engine-to-transaxle bolts tight?  I'm looking for a randomly intermittent ground connection from the alternator to the car frame an it normally grounds through the pedestal, then those bolts, then through the tranny-to-frame ground strap.

Sounds like a bad ground to me. Depending on age, battery cables may be shot.