around_midnight You didn't say if the system in the car is 12.0 volts or 16.0 volts? Are you running a 16.0 volt battery? A 12 volt system with a fully charged battery should show a charging rate of 13.7-14.3 volts at 2,000 rpms and a steady reading not bouncing. You are way out of the gate. You need to take the battery and Alt for a test. The battery could be internal shorted causing the high voltage output from the ALT. A load test will confirm this. A good 12.0 volt battery should be in the 12.3 to 12.7 voltage with a volt meter. Are you sure that the cables from the battery are tight to the soleniod, starter, and ground mounts?? Also make sure the the battery terminals and cables are CLEAN and tight at the posts. Do you have a side mount battery?? They can have problems withthe nuts that are bonded into the lead when they are built and cause crazy problems. The next thing to check, The belt and pulleys for slipping on the pulleys and glazing of the belt. Make sure it's tight but not or tight to cause a wearing out of the water pump bearing. Check for a coolant leak from the bottom of the water pump. This leak will cause the charging system to jump all over the place and yet when you look under the hood may see nothing. Is the car running undersize pulleys, like March??? They have caused some charging problems with 1 wire ALTs. If everything checks out OK, take the batery and ALT to 2 different places and have it check. Sears, Pepboys, Autozone, and R&S all have free checks but have testers are NOT CALIBRATED and try to sell you things you don't need like Batterys, Starters, Cables, and the Biggie ALTS.
They are all paid on commisions and upsales. Just be careful.
Rick L. Double check the ground and power wires for tight connection first.