Another FD cluster issue thread. The odometer works fine (when the key is in the acc or on position) and you can see the tach needle bouncing as the engine turns over/ attempts to start (it was the first start of a new engine/ build).

As soon as the engine starts the odometer goes blank and the gauges stop working, but the illumination remains, as soon as the engine is shut off the odometer comes back... any suggestions on where to start? Grounding issue maybe?

 

I would wiggle the key some back and forth while car is running to see if the connections in the ign switch have a problem. I also wonder if your alternator could have a problem. Could it possibly be putting out some AC current because of bad diodes or something. I edited out my suggestion for how to check the alternator. Don't know of a good way to check the alt without the right equipment. Not sure if it's that anyway. Maybe someone else will respond with some ideas.