How-to check a 25ft electrical wire point to point for ohms with a multimeter?

To check continuity on a 25ft electrical wire by yourself with a multimeter, start by making absolutely certain that there is no connection to power on the cable, and that both ends of the cable are completely disconnected from any kind of circuit, including ground.

Double check with the meter in volts mode that there is no voltage between any conductors or between any conductor and ground. You are doing this both to protect the meter from damage and to protect yourself from death by electrocution.

Now, in ohms mode, check between each conductor and from each conductor to ground. You should have inifinity ohms.

Short two conductors to each other on one end of the cable. Repeat the ohms test on the first side. You should find one pair of conductors with zero ohms, and all of the other combinations still infinity.

Repeat the test for all the different combinations of conductors. Eventually, you will be able to identify each conductor at each end. If, for example, there were four conductors, there would be six combinations of two wires. If you only have two conductors, you can also use ground to help identify one from the other, but now you have to be careful that there is no voltage differential between the two ground points.