I had to pull the starter motor to replace the oil sending unit. Put everything back together fixed oil leak but i now have a battery light on in the dash. Replaced the battery, alternator is good. Check voltage before start 12.45 volts checked after start 12.09 volts. I think i have a problem. Where do i go from here. Car has 218,000 miles on it never had any major problems. Car will run till it drains the battery
The alternator output wire is or should be attached to the positive cable stud on the starter. Check if it was reconnected when the starter was installed. There is a fusible link on the alternator output wire that may have blown.
It’s possible for the alternator to test good, but still not charge the battery. I think that’s what the battery light is telling you, and for the reason @Nevada_545 is saying. The alternator is no longer connected properly to charge up the battery. It tests ok, you can still start the car, but if you continue to drive it this way, eventually the battery will run down then you’ll be out of luck. For some reason the car’s designers must have decided to route the path from the alternator to the battery through the starter motor, likely to reduce the amount of the heavy gauge wire required.
Knowingly or unknowingly, you may have shorted out the battery and burnt through that fusible link to the alternator. Easy to do if you try changing a starter without disconnecting the battery.
Or you could have damaged the battery or alternator. For some reason it is not charging.
Check that output wire from the alternator to the battery for continuity, would be my first test.
Yosemite
All good comments and the consensus is that you have an alternator problem. It’s easy to troubleshoot and repair. I hope I don’t sound like Captain Obvious here. The 12.09 reading is a dead giveaway.