I'm trying to replace an outlet with a GFCI outlet and when I remove the wall cover and pulled out the old outlet it contained one neutral one ground and two lines on the hot side. The original outlet is located in a electrical box that also contains a light switch and I think the garbage disposal is also spliced inside this electrical box. I wanted to know if I should just pigtail the two hot wires together then connect them to the hot terminal on the GFCI line in and then connect the white neutral on the line in terminal? I know I only want to connect to the line side of the GFCI and not the load.
Is the tab broken on the hot side? Garbage dispisal, so probably a kitchen.
If the breaker double-wide? If so, you probably have a multi-wire branch circuit - so if you join the two hots you may find that the breaker trips hard as soon as you turn it on.
If you have a voltmeter, check the voltage between the two hot wires - it should either be 0 volts (they are the same phase) or 240 (they are opposite phase and it's a MWBC - pretty common in kitchens to meet the "two 20 amp circuits" rule.
If the tab is NOT broken and the voltage between the wires should then be 0, yes, you can splice and pigtail.