BiggyJ
I'm kind of lost on your discription. Are all lights controlled by one switch, or are they controlled by different switches from one place?
If you are putting your leads from your DVM on the two terminals of a switch, you should read 12ish volts with the switch in the OFF position. With the switch ON, you should read 0 volts across the terminals. A DVM may show milli volts with the switch on, but if you are reading anything over about .5 volts you have a bad switch.
If you have several switches at one place, check the voltage on the common wire to the switches. You should have 12 volts between the common connection and ground. Also check the voltage across the terminals of your fuse. It should be 0 volts. (maybe .5 volt on a DVM) If you are reading any voltage, you have a bad fuse or fuse holder.
When your lights are dimming check for voltage across the fuse or switch(es). If there is a common connection at several switches check for fluctuating voltage between that point and ground.
