[stevpre]

I am replacing an old light switch single outlet combo with a separate light switch and GFCI outlet. I have 4 wires in the box. 2 white, 1 black and 1 red. I don't believe there is a ground.
The house was built in 1944. When I pulled the old combo switch out, the 2 white wires and red wiere were on the top left screw. The black wire was on the bottom right.

Please help

[Stratmando]

If the 2 white and the red were on 1 screw, you will need to Totally Identify each wire.

Usually, the 2 whites would go on the white screw(recepticle large slot), and the black would hook to the recepticles(hot)small slot and 1 of the switches black wires. Then the red would connect to the other black wire on the switch.

This is if it is the combo that has 2 black pigtails, otherwise, hook to the terminals.
This is also assuming the whites are neutrals, black is the hot and the red being the switchleg to the light.
Good Luck