I have been repairing these monsters (I have three of them) for some time.
For your problem, Slowly use the switch to turn on the light. If you hear a click, then the micro switch appears to be working. If not, the metal activating level can be carefully bent out a tad to improve the switch contact area. Be sure the micro switch small screws are tight and the switch is not twisted.
The bulb is rather loose. It sits in the socket with two rather short prongs. You can carefully clean the bulb twin leads with Scotch Brite. Corrosion on the leads should then vanish.
The wire from the micro switch is connected to a cheap "tin" plate and tin soldered in place. It may look like a connection is made but the solder joint may be broken.
To fix this you will have to remove the entire back plate on the lamp assembly and slide the contact out of the back plate. Rough up the plate with fine sandpaper throughly, tinned with a 35 watt soldering iron and then resolder the wire back on the plate. This iron is VERY hot but the type of metal used needs to get very hot (briefly).
The batteries can be deformed by the extreme pressure exerted on the them when the light is completely asemblied. The ends of the batteries may BE DEFORMED AND COULD BE A PROBLEM.
One bad battery will result in poor operation. Measure each four battery bank. The battery voltage should exceed 6.3 VDC with good batteries. If the voltage has dropped below 6.0 VDC the light will not illuminte every time. Indivdual batteries should measure 1.6 to 1.8 VDC (Alkaline only). If you are using NiCAD, this may be your reason. The voltage is too low (although some do use them, I guess successfully).
Or, take it back and ask for a refund.
