The battery on my 95jimmy seems to drain if I leave it parked for the weekend

Until you find the problem, unhook one of the battery terminals whenever you turn off the engine.
Re-hook it up when you are ready to leave.
Without being there with a tester, I cannot diagnose the problem, but very often that particular problem is the alternator itself, draining the battery.
Many car parts stores will also check this for you free.
Try one in your area.
God bless your efforts.

Probably shorted put somewhere, making a connection and draining your battery.

yes

Most likely the alternator is bad. Best way for you to check is start it up, then pull the negative cable off the battery. If it dies the alternator is dead. As far as it draining when parked, I have replace a lot of the ignition lock set and keys because you can put it in the accessory position(All the way back) and pull the key out. Leaving on things like the radio.

drain parked or drains moving, you need to post that.
its got phantom drain.
easy to find with any cheap meter.
got meter?
my guess parked.
all ways are here, everyone.

http://www.fixkick.com/drain/drain.html

and toolls to find it, and techniques.

I guess my first question would be can you turn them off when it happens ? Most factory installed alarms would make all of the lights flash.
You could pull the fuse when you park the van until you find the problem.

There is a very good possibility that there is a short in the wiring that is causing the battery to be drained when it is off. There are a few auto parts stores that can do a complete electrical system check and they can test the battery drain when the car is off. These problems are usually caused by a faulty relay which leaves a component on when the vehicle is off. Or there can be a wire shorting. However, finding a short is often like chasing ghosts. I would recommend going to advance auto. The electrical scanner they have there can detect battery draining.

no when vehicle is off only a few things can drain the battery usually dome lights or headlights

The Auxilery battery is your problem. If you leave the door ajar, the battery will drain out. The Aux battery is quite small, and it is locted in the rear cargo area. We have found that once the Aux battery goes low, it is best to replace it. If the car is under 35K miles, it is still under the factory warranty. In any case, I would replace the Aux battery.