Water Heater Help 1975 tradewind
Rather than the red piolt button, your water heater has the function built-in to the blue knob. Turn the knob beyond the pilot setting until it stops -- be prepared to hold a lighting stick in the pilot area for several minutes while the gas makes the journey to the pilot -- once the pilot is burning steadily, release the button and move the knob to "run" and the main burner should light.
It looks like it may have been some time since the water heater was last operated. It would not surprise me if the air tube is filled with spider nests. The air tube is held onto the round main burner chamber entrance with one bolt which, when removed will allow you to gently bend the capillary tubes to that you can clean out any obstructions in the tube -- I found mine clogged with a solid mass of spider nests nearly 2" long at the beginning of this season (a long, flexible, small bottle brush is ideal for this cleaning operation -- mine is one made for cleaning test tubes).
Good luck with lighting your heater!
Kevin D. Allen
WBCCI (Lifetime Member)/VAC/Free Wheelers #6359
1964 Overlander International/1999 GMC K2500 Suburban (7400 VORTEC/4.11 Differentials)
1978 Argosy Minuet 6.0 Metre/1975 Cadillac Eldorado Convertible (8.2 Liter V8/2.70 Final Drive)