I want to check and possibly adjust my ignition timing. in the manual it says to earth the spark advance cut terminal. it is located near the firewall, but there is actually two connectors in the same spot. one is round and has a rubber knob at the top and the other is rectangular and has no cover and two terminals inside. which one is the one I have to ground as I heard if you picked the wrong one you'll stuff your fuel pump or sth.

cheers

lol Yes I made that mistake.

The ROUND one with the cap is connected to earth when checking the ignition timing. Single connector under the cap.

The rectangular one provides power to the fuel pump and it is connected to POSITIVE of the battery. Connect it to earth and the wire will start to smoke. lol It's useful if you suspect the fuel pump is dead, hook it u with key out and dive under the rear of the car and listen/feel for pump vibrations.

alright...I managed to adjust it. I got lucky a local mechanic shop let me use their timing light for free :)
could wrong timing result in cold-only issues like the ones I described in the 91 engine misfires threat? or can a plugged fuel filter cause problems only when the car is cold? I know I ask a lot of questions but I'm just trying to understand what my car does.
Cheers

If you have set the timing to 5 degrees BTDC with ignition cut and checked it advanced to 13 degrees with the ignition cut removed, then the timing is ok.
Misfiring when cold is more likely to be bad plug leads, spark plugs or a cracked/dirty/worn out distributor cap. Idle the car at night and look under the bonnet for arcing on the leads and cap. Also look where the high and low tension leads connect to the ignition coil.
Fuel filters have an easy live on the Magna, I changed out the original filter at 220,000 km and there was no difference. Not likely to be that.