first, you need to make sure the tank is full.
to fill the tank (if its "stock"...i.e. no add-ons/previous owner customizations), all you need to do is close any drain valves, hook up to city water, and turn on a hot water tap. If the tank is truly empty, it'll take a couple of minutes to fill it...you'll hear the air rushing out of the tap, as its displaced from the heater tank. once water starts running out, the tank is full. (it'll probably spit and fizz a bit until the last remaining air bubbles are out of the line...just let it run till consistantly smooth).
Look at the back side of the heater, and see if there is a by-pass kit installed. This would be a short pipe that connects the heater's intake and output fittings directly. If you have one installed, you need to make sure that the valves are positioned properly to allow the tank to fill.
(these are put in as an aid to winterizing the pipes; bypassing the water heater saves 6 or 10 gallons of antifreeze being pumped through the system; there's no need to fill the water heater w/ antifreeze, but you'd have to in order to fill the pipes...which do need it, if you live in a cold climate).
light the water heater:
see the box w/ the 2 blue knobs? the one on the top turns on the gas. turn it to "pilot", then hold down the red button next to it. this allows the gas to flow to the pilot. light the pilot w/ a match or long-handled lighter. It is on the end of the gas tube, where it bends around and goes into that hole on the lower-right corner of the heater. once the pilot lights, you need to keep holding that red button down for 30 seconds or so, until the pilot flame heats up the thermocouple, which is a little device right next to the pilot that senses heat, and sends a signal to the gas safety valve to stay open. When it heats up, you can let go of the red button, and the gas valve will stay open by itself.
once the pilot lights, and stays lit after you release the button, you can turn the control knob to "on", and the burner should light. all done.
the other knob is simply the temperature setting. fairly self-explanitory.
'73 Safari 23'
'00 Dodge Ram 1500 4x4 QC