I bought one of these

http://www.ebay.com/itm/New-Oil-Pres...53.m2749.l2649

because my gauge was reading at the maximum.

I installed it and now the oil pressure reads very low and even triggers the oil light?

 

Stay on top of the dipstick until you get it sorted. You may want to go with oem.

 

How does one even check the dipstick correctly? Oil is just all over it by the time it comes out.

 

Stop the engine, wait 15 minutes.
Open hood, pull oil dipstick. Wipe completely and reinsert fully.
Remove again and hold oily end slightly lower than handle.
Compare oil level against "full" line on stick.

Good luck!