After alternator replacement, brake and battery lights are on, have checked charging circuit, ok, also O2 sensor light is on even though I have replaced the O2 sensor after 80,000 miles. How do I reset ECU to get these lights to go of?

no never ,,,think you have a faulty alternator diode ,causing the battery to drain ,,,best advice ? call a local mechanic and get them to check it out for you

ok so your acid level in the battery needs to be checked if its at the right level get another battery because there are dead cells in it. if the alternators good check it to be sure even new parts can be bad. ok same problems with a good alternator bad battery. Hope this helps

Brake Light. Make sure you are not driving with hand brake on. Check brake-fluid level. Top off brake fluid if low and make appointment to check brakes. Driving with brake light can be dangerous; deal with this soon. Call tow truck or drive carefully and slowly to shop.
ABS (antilock brake system) Light. Indicates either low brake-fluid level, stuck brake caliper or faulty ABS. Check brake fluid and make appointment to get brakes checked. Call tow truck or drive carefully and slowly to shop.
Oil Light. Either engine is very low on oil or there is no oil pressure. Pull over and turn off engine immediately. Check oil level and add oil if low. Turn engine back on to see if light has gone off. If oil light is still on, bad oil pump (no oil pressure) is likely. Call tow truck.
Check Engine Light. Car's computer senses engine problem. Difference in performance may not be noticeable, but make appointment to have car diagnosed. This usually cost around $65-$75 to do. OK to drive. If problem is serious, computer may switch to limp-home (low-power) mode and you won't have option of waiting to bring car into shop.
Air Bag Light. Get air bags checked. Problem could prevent them from activating in accident. OK to drive, but not safe in accident.
Battery Charge Light. Alternator is not charging. OK to drive, but turn off any unneeded electrical devices (radio, heater, defroster) and avoid starting engine more than necessary. Bring car into shop soon to avoid getting stranded. When alternator is not charging, battery loses charge and car stops working.
Emissions Lights (O2 sensor, EGR, check emissions). Depending on car model, these lights may indicate problem with emissions sensor or may light up at certain mileage, usually 60,000 miles (100,000 km). Get sensors checked. OK to drive. If problem exists, car might get poor gas mileage.
OBD Tools 365 Days Shop

A red light on the dashboard can mean you should stop driving right away, or you may have a little time before you have to bring your car into the shop. Know what's what so you don't get stuck.

1. Critical Warning Lights
   • 1 Brake Light. Make sure you are not driving with hand brake on. Check brake-fluid level. Top off brake fluid if low and make appointment to check brakes. Driving with brake light can be dangerous; deal with this soon. Call tow truck or drive carefully and slowly to shop.
     
   • 2 ABS (antilock brake system) Light. Indicates either low brake-fluid level, stuck brake caliper or faulty ABS. Check brake fluid and make appointment to get brakes checked. Call tow truck or drive carefully and slowly to shop.
     
   • 3 Oil Light. Either engine is very low on oil or there is no oil pressure. Pull over and turn off engine immediately. Check oil level and add oil if low. Turn engine back on to see if light has gone off. If oil light is still on, bad oil pump (no oil pressure) is likely. Call tow truck.
     
   Maintenance Lights
   • 1 Check Engine Light. Car's computer senses engine problem. Difference in performance may not be noticeable, but make appointment to have car diagnosed. This usually cost around $65-$75 to do. OK to drive. If problem is serious, computer may switch to limp-home (low-power) mode and you won't have option of waiting to bring car into shop.
     
   • 2 Air Bag Light. Get air bags checked. Problem could prevent them from activating in accident. OK to drive, but not safe in accident.
     
   • 3 Battery Charge Light. Alternator is not charging. OK to drive, but turn off any unneeded electrical devices (radio, heater, defroster) and avoid starting engine more than necessary. Bring car into shop soon to avoid getting stranded. When alternator is not charging, battery loses charge and car stops working.
     
   • 4 Emissions Lights (O2 sensor, EGR, check emissions). Depending on car model, these lights may indicate problem with emissions sensor or may light up at certain mileage, usually 60,000 miles (100,000 km). Get sensors checked. OK to drive. If problem exists, car might get poor gas mileage.
     

I have a Daihatsu rocky I'm working on with the same thing going on with the o2s light. Staying on .. 88k miles on a 1990 1.69l .. If you find how to turn it off wright me

You need to know what codes you have stored
Your O2 Sensor, may not be the problem,even though you get an O2 Code. That may just be the symptom

The alternator has a bad diode in the diode bridge in the alternator,this turns the light on,even though the alternator checks good,and is charging correctly,there is a bad diode,this diode ,along with others,changes ac voltage to dc voltage,if not replaced,it will start causing components to go out.

The surging is from the alternator not charging enough volts.Check the volts at the battery,while it is running,it should read about 13.65 to 14.25 volts,if it is less than this replace the alternator,it should be checked with the head lights on,and fan on high blower setting.

common problem with the reulator going bad in alternator causing this to happen even though the alternator still charges

You have to test the alternator output, should be about 14 - 16 volts.

Test your battery too, fully charged battery should be about 13 volts.

If these check out ok, the problem is the sensor or the wiring in the sensor circuit