I would also look for the earth as a possible source of your problem.
I had a similar (ish) problem where several components were not working properly and some intermittently and I chased around the loom for ages looking for chaffed wires, shorts, water damage etc. Eventually, i bought myself a Sealey PP100 power probe which hooks up to the battery + & - and allows you to power up or check the earth of any 12v component on the car. I then went and powered some of the major components like my headlights, using the power probe on them which bypasses the car loom and found that all the lights etc were working fine and worked my way back the loom checking all the fuses, joints etc and using the Landrover wiring diagram, went to the pages that show the location of all the earth points in the car and found a loose body earth which was the source of my problems. I made a new one out and remounted it and cleaned off the corrosion on the mount and everything was fixed.
Hope that helps a bit.