Have been chasing an electrical problem and believe we have it isolated to the lights. Here's what happens:

* Battery holds a charge and starts perfect as long as we don't use the lights. Can let it sit for days and it fires right up.

* When we drive it with lights, we can make stops and it will still start when we get back in.

* After letting it sit at home for a day or two after having driven it with lights, it's dead.

* Put it on the charger, charge the battery and it holds the charge for days/weeks as long as we don't use lights.

Any ideas?

Assuming this is a first gen Camaro, I would first make sure the belt/s are not loose and the alternator pulley is not loose. When you put a load on the charging system (turning the lights on)can cause enough slippage to cause the battery to be undercharged. Then have the battery load tested and the alternator and voltage regulator checked. If all are ok, my next guess would be the light switch. The rheostat for the dome light may be the problem. Park the car after using the lights as you would to simulate the no start problem and do a parasitic draw test (easier than it sounds) Disconnect the positive battery cable and put an amp meter between the positive battery terminal and the positive battery cable. (DO NOT ATTEMPT TO START THE CAR) unless of course you want to watch your amp gauge blow up! You can then play with the light switch to see the draw on the gauge. Opening the doors and turning on other things will cause the gauge to move to the negative side of zero. With all power off, the gauge should read zero. If it doesn't, check everything electrical by pulling one fuse at a time until you get a zero reading. Things that are not fused by regular fuses, like lights will have to be unplugged to check for a draw on the battery. If you see that unplugging the light switch with the lights and dome light OFF allows the gauge to read zero, then you have found the problem. I'll admit, this is a little confusing, but if you understand this, you can handle most electrical problems in the early cars. One thing to note, 99 percent of the electrical problems I fix are from bad grounds.
Hope this helps.
Jim

Desert, great advice from Jim above. One quick thing to check that was causing me a problem very similiar to yours - check and make sure that you have the voltage regulator grounded. My car would hold a charge fine and I knew the battery, alternator and voltage regulator were good (they are new and I took them in to NAPA and had them double checked). And as long as I ran the car with no lights or heater going, everything was fine. But if I turned the heater or lights or both on, the battery went dead. I double checked the wiring diagram and found that the voltage regulator must be grounded. I used the correct rubber-insulated retainers to attach the voltage regulator to the radiator support so I needed to attach a wire from voltage regulator to rad. support. All is well now. If your voltage regulator is sitting on the rubber attachments and has no ground wire, this may be your problem. By the way, my car is a '67. What are you working on?

Sorry for the delay in saying thanks. Got called out of town on business.

We'll take a look at it this weekend and see what we can find out.

Denver RS/SS:

We've got a '68 coupe. Was a plain jane with a bunch of rust, now nice (although no where near stock). We built it the way we wanted.

Had a replacement 350 when we bought it, still has the PG.

I'll send you a pic to you e-mail address if I can.

Thanks again.