New Electronic Speedometer issues

[Myasylum]

So, i bought the new instrument panel gauges and everything worked for 214 miles, then the speedometer quit working.
I really hate taking that dash apart but ok, I'll do it again. Tried a new ground still didn't work. So just as a curiosity while driving I was touching to what thought might be a good ground. What works is the tab in the ash tray! Wtf?
The original ground is connected right to the block! Why without the ash try work?? Not exactly where I want a permanent ground.
Any ideas what might be going on here?
These a Autometer gauges. Everything else works with its proper ground. I just find this speedometer to be weird, or possibly just me, idk??
Thanks!

 

[MoparLeo]

Where is the speedometer getting its power?
The engine should be grounded to the block and body.
The ground cable should have a stub that goes to the radiator support and there should also be a ground strap between the bellhousing and the firewall.

 

[Myasylum]

Yea, I seem to be missing a ground from the block to the firewall.
Yet all the other grounds for the dash seem work.
The speedometer has power. It just isn't reading pulses unless connected to the ash tray.
This even works...

 

[kiwigtx]

Where and how have you run the cable that goes to the speedometer drive unit?

Is this a Hall Effect speedometer drive?

 

[Myasylum]

This is a 2 wire speedometer drive.
Purple reads pulses and yellow is ground.

Like I say, it worked fine for 214 miles.

I just added the ground from the head to the firewall. Didn't do anything.

I'm tempted to cut the ground wire and ground it someplace closer to the sensor. Like right to the transmission maybe??

 

[MoparLeo]

You just need to connect the ground to the dash frame then. The ashtray is just attached to the dash frame.
What is the other end of the ground wire attached to ?

 

[kiwigtx]

This is a 2 wire speedometer drive.
Purple reads pulses and yellow is ground.

Like I say, it worked fine for 214 miles.

I just added the ground from the head to the firewall. Didn't do anything.

I don't know if the instructions tell you to do this....but if it was my car I would do the following.

Get two new pieces of yellow and purple 'Hook-up' wire - typically light duty instrument cable.
Cut them to be at least one and a half times longer than the length you need.
Put one end of each wire into the chuck of a battery drill.
Get someone to help you here - hold the other ends out straight.
Pull the trigger on the drill until you get a nice and neat twisted pair.

(The act of twisting the two wires will shorten them.)

Now, re-install the correct terminals on the end, and run the ground wire to a solid ground nearer to the dash mounted speedometer.

The reason for the twisted cable is to reduce and/or eliminate any induced harmonics or dirty electrical signals getting in.
Trust me on this .....it works in other applications on all sorts of sensitive measuring devices.....it should work for you on the speedometer.

I wired a '32 Ford Hotrod a few years back and had the same issue. To fix that one I used a twisted pair instrument cable with foil shielding and a drain wire.
It works.

 

[kiwigtx]

You're

 

[Myasylum]

This is the sensor I have. Wire color is just different.

 

[kiwigtx]

This is the sensor I have. Wire color is just different.

View attachment 1525122

Continue the twisting all the way to the speedometer as I said above.