Not sure which you are trying to find out so will give you two ways. Case one will tell you what pair on the receiver wall side goes to a given pair on the speaker side. Case two will let you lable the pair between the receiver wire pair side and the speaker pair side for polarity (+/-) so you can get the phase right when you hook them up.

Case 1: Bunch of cables and finding what goes to where:

You have a group of wires coming out of the wall at the receiver end and none are labled, how to find out which ones go to which end.

A. Go to all of the "other" ends where there is just one pair of wires for a speaker and make sure none of them are touching each other, that is, not shorted.

B. Pick any pair, say Right / Rear. Go to the speaker end, with no speaker attached of course, and twist that pair together. (short them)

C. Set your DVM/Ohm Meter on any Ohm Setting (some have a continuity beeping setting, use that if you have it).

D. Go to the batch of wires and measure pick one end, put one of your Ohm meter wires on that end.

E. Then touch all other ends with the other meter wire until you get a reading of very few or 0 Ohms or a beep if you have that mode, that is a pair. To be on the safe side, always check all of the other wires to make sure none of them have a reading, I have see some where the return wire was made common to a pair.

F. Mark that pair as what ever they are, in this example, mark them Right Rear.

Case 2. You know which pairs go to which location but now need to know which wire is which so you can get +/- right for phase.

A. Get any reasonable battery, AA/C/D battery and tape a wire to each end, make sure to either use two different color wires or mark them + / - .

B. Set your meter to the DC Volts Scale as close to 2VDC as your meter has, for this we'll say you have a 5VDC setting, does not really matter within reason.

C. Test to make sure your meter probes are connected to the meter right by touching the red / positive probe to the plus side battery wire and the black / negative probe to the minus side of the battery.

You should get somewhere around a PLUS +1.5VDC reading. (If you get a Minus -1.5VDC reading then either your probes are backwards or how you labled the wires you taped to the battery.) Note the actual voltage reading you get, for this example we'll say you got a +1.5VDC reading.

At this point you have a "known" condition.

D. Make sure none of the pairs or wires on the receiver end are shorted / touching.

E. Pick an end on the speaker side now, again we'll go with Right / Rear and hook the battery to the two wires. Plus side to one wire, minus side of the battery to the other wire.

F. Go to the receiver sire and put the meter probes on the Right / Rear pair. (See Case 1 if you don't know which pair that is...)

G. Measure that pair putting the red probe on one wire and black on the other. You should get about 1.5VDC reading. If you get PLUS +1.5VDC then lable the speaker wire + that the red Probe is on. If you get a MINUS -1.5VDC reading, lable the wire with the meters black probe as Plus (+).

H. On the side with the battery, lable the wires the same as the battery end you have them hooked to + on one and - on the other.

I. Repeat this process for all pairs with the same battery.

Notes:
a. If no pairs read about 1.5VDC then you have an open or have not found the right combination of pairs yet.

b. If any pair have a substantial drop, like more than 0.25 or so VDC then your wires are either reallllly long, not the best quality, or the ends might be still slightly laminated or have paint or varnish on them giving you a poor connection, in any event with a fresh battery your loss should be very close to 0 and read what you read from the battery itself.

That is it.