I have a 95 Mazda B2300 2.3L The battery light is flickering, but the alt is new and the output is 13.7 volt. what could be the problem?

You have a defective alternator, that what is most likely causing the flickering light. A voltage output test will not reveal this.

You should get 13 to 15 volts output .

I think you mean 13 volts on the gauge.
Its a simple matter to check alternator output with a meter. The battery can be load tested with a testing device at most any auto parts store.

if they are both fine then the conection could be bad. or there is a fuesable link in the wire from batt to alt. test the alt power wire while running on car for power over 13 volts. if there is power on the power lead then your fuesable link is blown. just replace the alt wire to the batt and you will be on the road

When it is running,put a volt meter across battery terminals. You should see 13 + volts if alternator is working. Also put an ampere meter in series with a battery cable,key off, engine off, and you should see less than 40 to 50 Mili-Amps. If more,start pulling one fuse at a time,untill you find the circuit that is draining the battery

The alternator may not be charging the battery. Jump start it, and use a volt meter at the battery, red lead to positive and black to neg. The meter should read between 13 and almost 15 volts, any lower than 13 volts, the alternator is no good. (this is done with vehicle running).

Check your battery connections and do a voltage test to battery with engine running lights off, then check with lights on. You need a minimum of 12.5 volts but should have 13-14 volts even with lights.

The alternator should be installed in the truck for voltage testing. Proper voltage with engine running is 13.5 to 14.5 volts at the battery terminals. If it reads 12.6 volts, the wire between the alternator output and the battery is open.

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