Just looked in my manual (I own a MT180D).
Don't see any additional fuses other than the fuse box.
Recently I also had some electrical 'gremlins' and discovered that some fuses were making bad contact.
I resoldered the leads going into the clips that hold the fuses in place and that cured my intermittants.
In my case my battery was flat dead after using the tractor for about 2-3 hrs as I was getting all drain and no charge.
You state 'field coil'? do you mean the regulator (PN RQB2220D1)
You know at the current age of these tractors we have to be on the lookout for corrosion induced electrical problems, especially in humid climates.
I, for one, have had over the last year or so, probably wire brush cleaned just about every contact and bonding (ground points) in an attempt to maintain my Mit up to snuff.
A dielectric greese on exposed contacts will help eliminate lots of problems.
(Even vasoline is better than nothing)
Good luck!
