If you hit the starter and it clicks, it means there is not enough battery voltage to engage the starter. You have less than 10V in the battery, letting the lights work. You need to check the voltage from the alternator to make sure it is putting out around 14V when your car is idling.

The switch plate behind the key lock at the steering wheel may be getting worn and in need of replacement. Easy DIY job. Just remove the plastic cover behind the steering wheel and R&R the switch plate. About $30 at your "friendly" dealer.

If you park outside in the sun, volkswagen makes a solar panel trickle charger which can be bought at the dealer or on ebay+shipping for about the same price. Otherwise, go to Sears automotive for a plug in type.

When you get your check valve replaced, it is a good time to replace the gas filter at the same time.

Good luck,
Klaus
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98 V70Rawd(101Kmi), 95 854T(85K mi), 75 164E(173K mi)