I need to find an 1998 oldsmobile regency wiring diagram for free online the battery does not stay charged i have tried switching batteries and still does the same thing its only staying charged for the amout of time on the charger

On earlier charging systems that used a separate voltage regulator some used a separate unit to control the ignition light and this might be the trouble - check with a wiring diagram.

If it is a an integrated regulator type the warning light wire connects directly to the alternator and all it does is ground the earthy side of the battery light through the rotor winding until the regulator begins to energise the rotor via the auxiliary diodes.

With smart charging systems and probably with later CANbus systems the battery light is controlled by black boxes.

http://www.tomanual.com/search/diagram+for+1998+oldsmobile+regency+cooling+fan+control
http://www.automotix.net/autorepair/diy/1998-oldsmobile-regency-wiring_diagram.html

Check battery and connection,when start up try move steering wheel left to right.

YOU HAVE TO FIND OUT HOW TO GET YOUR CODES RESET TRY ADVANCE OR AUTOZONE FREE DEALERS 99
OR YOUR ALTERNATOR WAS THE REAL ROBLEM AND IT IS NOT PUTTING CHARGE TO YOUR BATTERY STILL GO TO AUTO STORES THEY WILL NORMALLY CHECK THAT STUFF FREE OF CHARGE

Do you know if your 98 has adaptive lamp monitor module ? Do you know how to read a wiring diagram ? Thier is no relay for the headlmps on your vehicle !
Do you know how to test automotive electrical circuits with a DVOM - digital volt ohm meter ! Free wiring diagrams here http://www.bbbind.com/free_tsb.html Enter vehicle info. year , make , model and engine size . Under system click on lighting then under subsystem click on headlamps . Now watch these videos on electrical testing and basic's . These guy's are professional tech's .
Electric Testing Techniques You Need to Know

The Trainer 32 How To Read An Automotive Block Wiring Diagram
Basic Electricity for Service Techs Ohm law Current Flow Opens Shorts

You need to test your charging system circuits at the alternator. (see diagram and instructions)

BLK is the cable to the battery POSITIVE terminal - this is hot at all times.
PINK/BLACK comes from Fuse #5 (15 Amp) in the relay center under the right side of the instrument panel. This wire is hot (battery voltage) with the ignition switch in the RUN, BULB TEST, or START positions.
BROWN comes from your instrument panel and is protected by Fuse #16 (20 Amp) in the instrument panel left side fuse block. This wire will have slightly less than battery voltage with the ignition switch in the RUN, BULB TEST, or START positions.
If any of this is not as described, let me know what you have found and we can continue if needed.

the filter is in the filter box next to the battery eather unscrew the screws if it has them or pop the clips it will open replace the filter

have battery tested most auto stores offer this service for free if battery good start looking at accessories or something plugged into lighter or lights in glovebox/underhood

Check fusable links in your battery cable and starter wires. Do you have power at the starter where the positive cable attaches? Your battery is good? Do you have any power anywhere else?

Are the battery cables corroded or otherwise no making a good connection? Clean them with a cable end cleaning tool avail at any auto parts store for around $5.00 and try it again, I bet the that is the issue, also charge the battery and have it tested at Kragen, they do it for free.