My GFCI tripped and would not reset. I jumpered out the outlet and all power returned to normal. I assumed it was a defective GFCI so I replaced it. Same problem. Power is available at the line side, but when the reset button is pushed the GFCI just trips again. I reversed the wires, thinking that maybe I had line and load reversed, but that didn't work either. I jumpered out the outlet again, and the power came back on downstream. Any suggestions??
Never do random things in electrical. You will stumble upon combinations that will work but will kill you.
Pause to learn what exactly it is you are doing. Only then proceed.
OK, so you had a GFCI that was previously installed and worked before, and now suddenly is tripping.
The most important point is that GFCI devices are capable of protecting downline loads. Those are the ones that are now dead.
First, unplug all the appliances that are downline from the GFCI device, and plugged into it if it's a receptacle. That will clear up 99% of your problems in a "didn't trip before, now does" situation. Once it clears, start plugging stuff in again When you plug a certain appliance in, it will trip. Try that in a different GFCI and see if it still trips there. Off to the appliance repair it goes.
Second, unwire the GFCI device and disconnect and cap off the
LOADwires only. Now, see if the GFCI device clears. If it does, the problem is in either a hardwired device (lamp, fan etc.) or is in the wiring itself.
Then, you reconnect LOAD and start removing hardwired devices. You need to remove both hot and neutral to have an effective test. Obviously when you remove a device and it stops tripping, you found the problem.
If you have removed all hardwired devices and it still trips, then you must do a bug-hunt for any crossed neutrals - anywhere a device uses one cable's hot yet another cable's neutral. Also check for this in the GFCI itself. If you get stuck or confused, take photos and post them here.
Third, if the GFCI device still won't clear with nothing on LOAD, and (if it's a GFCI receptacle) nothing plugged into it, then you definitely have a bad GFCI. Otherwise, you do not.