I replaced GFCI in garage thinking it was defective due to repeated tripping. After attaching my line connections to GFCI I attached my load lines. After attaching the white wire I attached the black next and immediately the GFCI trips. After reseting I tried it again and it trips again. What is happening to cause the tripping on the load side connection.

 

Welcome to the forums.

The black load wire is touching ground somewhere.
Check from that wire to ground with an ohmmeter. There should be no continuity.

 

Did you connect white neutral wire from the load to neutral side of the load terminal?
This is a common mistake when replacing GFCI receptacle.

 

There is a fault on the LOAD circuit. Check all the LOAD devices for moisture or neutral to ground faults.

 

Did the new ground fault circuit interrupter receptacle work correctly (including supplying power to a light or other device plugged into it), with the power cable connected to the line terminals and nothing connected to the load terminals?

Make sure that there is no pigtail or other interconnection between the white wire connected to the load neutral terminal and the white wire connected to the line neutral terminal of the GFCI unit.

Also, neutral touching ground further along the continuation subcircuit (connected to the load terminals) will cause the GFCI to trip.

 

Pete, if the black load was touching ground it would trip a device ie breaker or fuse.
Geo

 

Black touching ground will trip GFCI as well. That still is a ground fault and usually GFCI will trip before the breaker trips from overload.

If the GFCI didn't trip immediately before replacing GFCI receptacle, I still suspect incorrect wiring.

If there are any receptacles outside, open all of them and check if there are any bugs nesting inside. I once had ant nest in one and had random tripping of GFCI. Took some time to figure out what was causing it to trip because it wouldn't trip on a dry sunny day.

 

Black touching white will always trip breaker.
Black touching ground should trip the GFI.

 

Black touching the ground will trip the breaker (and maybe the GFCI)
Black touching the white will trip the breaker
White touching the ground will trip the GFCI (and AFCI)
Leakage of 4-6 milliamps of current to ground from neutral or ungrounded conductors will trip the GFCI