Older LUV's have a weak link in the electrical system, the fusebox. The terminals the wires connect are riveted to the fuse holders. A little age and corrosion, and you get electrical intermittents. I solved mine by taking it apart and soldering the joints. Others have cleaned it with lemon juice, and others a new fuse box. Yours may be new enough that they fixed the problem. You need to make sure power into the fuse box makes it back out. Power should flow from the battery to the key, to the fuse box, to the coil and VR.
On the 6 wire plug from the VR white red = W = fuel pump and charge light, white = W = ignition, white blue = B = battery, black = E = earth, British for ground, white black = F = field, the stem of the Tee connector to the alternator, and white green = N = field ground, feeds back to the VR.
This may help,
http://www.luvtruck.com/PDF/Series6.pdf