If you still have a dynamo it should be easy to switch to the battery negative earth norm. You then have a greater range of solid state instrument regulators. I used this one on a Land Rover.
![[Linked Image]](https://i.ebayimg.com/images/g/pdsAAOSwj11g--aA/s-l500.jpg)
Note the one you originally ordered appeared to be electro mechanical, likely as below.
![[Linked Image]](https://3.bp.blogspot.com/-2mjxBL-TwYY/TpiIM2ElMeI/AAAAAAAAAHc/5EqeO5xO69U/s320/1.png)