Then it will always blow Andrew.
For the gauge to blow in this way there must be an earth through the gauge at 0 ohms (well obviously slightly above 0).
This must be in parallel with the other earth so that when the other earth doesn't work, this one takes its place.
If they are in parallel then a proportion of the current will flow through the gauge even when the other earth is working properly.
The resistance of the main earth and the earth through the gauge will be similar, certainly not orders of magnitude different.
If we look at the main earth while the starter is cranking. Let's say it's 100A and 0.01 Ohms. That's a PD of 1V. That 1V split across the two earths in parallel will fry the earth through the gauge anyway.
I'm happy that my argument could well be false, but am interested in working out exactly why!
The thing that is driving my thinking is that poor earths are the bane of Caterhams. If that resulted in the gauge taking the strain as it were and frying, it would be a very common occurrence and it's not!