OK, got a cheapie 12" sub in a small sealed box, and an old 2channel amp (not sure of power), that isn't marked as supporting bridging; what should I do?

Amp is marked as 4ohm x 2, (-) poles are next to each other, which from the brief search that I've done isn't how most bridgeable amps are laid out; usually (+)(-)(+)(-)?

Should I just use the one channel, attempt a bridge of some sort, or run the channels in parallel?

PS. In case it isn't blatantly obvious, I have no clue about subs and amps; I've done a lot of general electrical work, and standard house stereo stuff, but never really touched anything to do with bridging etc.

Got a model number or brand for the amp?
Listen to it bridged and listen to it un-bridged and if its the same output (or you get no output) then you can't bridge, if bridging is louder well yeh pretty self explanatory :).

Pretty sure the amp's one of those ones Crazy Clarkes used to sell with a pair of 8" woofers, it's an XLogic XL652P, which searches reveal absolutely no info on (no hits fullstop).

Because of the non-standard layout of the outputs, I don't know which terminals to attempt to bridge to begin with; do I connect the sub to both (+)'s, and connect the two (-)'s together?

Just had a look at the sub's box, and it's 4ohm also.

I've pulled the amp apart and it looks like a reasonably simple circuit, so could possibly come up with a schematic if need be.

PS. Yes I know I won't get earth-shattering sound, I'm just after a tiny bit more bottom end, and couldn't justify spending more than my stereo's worth on it.

Because of the non-standard layout of the outputs, I don't know which terminals to attempt to bridge to begin with; do I connect the sub to both (+)'s, and connect the two (-)'s together?
Pick someting with tonal variation of your source so it's a bit easier to notice the difference.
First try 1 channel by itself (the 1st + and -) and take note, then, just for thrillls, so the 2nd channel. Take note of the output/SPL.
Next, connect to the + of CH1 and the - of CH2. Replay your test music and see how you go. If there's not much difference you can try the - of CH1 and the + of CH2, but's unlikely to make a difference.

Cant expect too much from cheap gear...

Buy jaycar if you're on a budget

I'm not expecting much. I just figure that as I have a 2channel amp, rather than leaving one channel unused I may as well see if I can tie in the 2nd channel as well, if purely to reduce any strain on the amp.

I have $30 6x9's, $20 6.5's, and stock 4's, and am happy with the output and quality I'm getting out of them. And no I'm not tone-deaf or clueless. The audiophiles out there just seem to think that if it's under $5K's worth, it'll sound like ****. If I wanted that kind of sound quality whilst driving, I'd get a helmet with noise-cancelling 7.1!

I'm not expecting much. I just figure that as I have a 2channel amp, rather than leaving one channel unused I may as well see if I can tie in the 2nd channel as well, if purely to reduce any strain on the amp.

I have $30 6x9's, $20 6.5's, and stock 4's, and am happy with the output and quality I'm getting out of them. And no I'm not tone-deaf or clueless. The audiophiles out there just seem to think that if it's under $5K's worth, it'll sound like ****. If I wanted that kind of sound quality whilst driving, I'd get a helmet with noise-cancelling 7.1!

Ok. I don't think that is correct. Depending on the set up, a system might have a downfall. It is not the component cost that will have the ultimate say in quality. You can make a great set of components sound crap if not mounted incorrectly.

My gear component wise has only cost about $2300. Now the extra's have cost the same if not more ( wiring / battery / Sd / Custom Sub box / Tuning ). You take a short cut and you will notice.

Well, I've got it hooked up and sitting in the cargo area (aka "boot"), seems to do the job. Just running the one channel, but is more than adequate for what I wanted.
Total cost, about $45, including amp and wiring.