OK, here is how it worked out for
my truck with
my ammeter.
I placed a 50mOhm resistor in series with the 12AWG red wire to the terminal block. Keep in mind that this is a prototype, the final installation will be well hidden under and look original.
With the headlights on and the fan on, no motor running, the ammeter reads like:
That is probably too aggressive. My final will be 25mOhms I think. I bought two of those 50's and I will place them in parallel with each other.
I also do not like the 4A fuses, I am going to add a similarly hidden 1A fuse in series to better protect that meter. A 4A fuse won't blow until 6A.
In the end, I think my implementation will look like:
and for those interested, here is why I don't like the 4A fuses. The chart uses logarithmic axes, X axes is impotant in particular:
