I have replaced a ceiling light fixture. I matched black to 3 black in the ceiling box that were twisted together and capped. I matched white to 3 white in the ceiling box that were twisted together and capped. There is a separate ground. Now, the wall switch works opposite of what it should. When it is in the down position the light comes on and the circuit trips. Should I reverse the connections putting the new fixture white to the black in the circuit box? Thanks for your help.

No, you should correct the wiring in the ceiling.

If you or can get a volt/ohm meter it will be very helpful to you.

In the ceiling, there will be on cable (Black/White/Bare) that supplies a continuous Hot line. Now turn off the breaker supplying this line in.

Next, determine which of the other two blacks are part of the switch circuit.

Connect one black conductor to the constant Hot (black) in the ceiling. The other black (switched) goes to the black on the light fixture.

The white from the fixture connects to the white from the "Source" cable.

The bare copper wire connects to the bare or green wire from the fixture.

Turn the breaker back on and test the switch. If it works correctly, then button every thing up, you are finished.

If the switch still is out of orientation, go back to the ceiling connection and after turning the power off, swap the black switch conductors. Take the black from the fixture and place it on the "Hot" line. Place the black from the "Hot" line to the fixture.

Turn the power back on and the switch should now work correctly