Yeah, i know what you mean.
I just picked one of them (either), although, i think i did a bit of a search thru the forums and each wire handles 3 pistons, wire 1 the front 3 near the grill, and 2 the back three near the driver......i think from memory.
..and apparently the back 3 have the most 'noise' so i chose that one.
Just pick either one, and most people think the value coming out of it is total crap anyway so i wouldn't be too worried about it.
If your getting the SAFC dyno tuned (i did), they listen for pinging anyway without using that readout value.
(Heaps of info on the SAFC if you do a search)
Catchya!