Channel imbalance with turntable playback

"...There is only one right position for all cables in your system..."

No you can swap two sets of cables and get back to normal stereo. You can swap phono pre and pre or pre and amp, etc. 

You can swap whatever you want, but if you’re listening to a stereo source then your Left speaker is L channel and your right speaker is R channel, just like on the master. There is a simple test on any test record, the voice recorded on LP will tell you which channel it is originally, and if the voice appeared from the wrong channel then you must swap cables L R channels.

There is also phase and out of phase test, in polarity and out of polarity test.

Those TEST records are made for system adjustment.

If you want to know what's right and wrong USE A TEST RECORD!

@chakster even if I do find phase or polarity problems, how would I go about adjusting those?

So I’ve been having a slight channel imbalance for awhile now. Vocal tend to lean left and just overall left leaning gain.

Some records recorded this way

I swapped the L&R input on the phono preamp and it sounds way more balanced.

If you prefer to hear vocal on opposite side how do you know how it was recorded ? You can prefer what you're hearing on one particular record, but how about some other records ? 

You need a MONO record to check your system for imbalance. Mono signal is equal in both channels. Play MONO LP and try to detect imbalance. 

Also compare with digital source

even if I do find phase or polarity problems, how would I go about adjusting those?

Your cables have color code, equipment have L/R marks and color code, cartridge pins have color code too. If you made a mistake once then everything else is wrong, you must find where you made a mistake (check all cables in your system).