[Cobra289]

Hi Ben,

I think that you are running in interesting electrical problems.
I go for general earth problems, if the license plate fails, it doesn’t mean that the earth there is the problem, it can be a general earth in your wiring, and due to that other systems can also have funny behavior too.

I would advice to go first and check the alternator, provide at the alternator body a good earth and not via possible support brackets.

Engine, check and double check the earth, the best place are the heads, why because you will be at a suitable area and less possible insulators to the distributor.

Dash earth or earths, here there are a lot of possibilities for problems, like painted surfaces, threaded bolt connections are the best, on top of that use of “silicone paste”. Not the solid compound but the dielectric paste will solve for the length of years for a good connection and will protect the blank steel or the prone to rust connectors.

If you turn your indicator light and you see that the heads light goes on or other funny behaviors you can say for 100% that is an earth problem and the positive electricity has found a way to connect to earth via the positive wire.

Craig has mentioned a good way how to find a possible drain; I would advice to follow that practice.
If that doesn’t help than is time to see a doctor.

I hope that this help you.
Regards,
Cobra289