There is no special formula for tire pressure in regards to the load of your trailer as you normally want to inflate the tire to the maximum cold psi for the best performance.
However, if you are not getting that, and your trailer is bouncing then you can try reducing the air pressure on a 5.30R12 tires like the Taskmaster # TT53012C which like your tire, has a max of 80 psi. The maximum capacity of these load range C tires is 1,050 lbs each so if you have the same or similar tire you... view full answer...
The etrailer Motorcycle Carrier for 2" Hitches part # e98873 weighs around 58 lbs. This is actually one of the lightest motorcycle carriers we offer. view full answer...
I reached out to the manufacturer who said the top part of the Prodigy P3 # 90195 in your photo is not supposed to come off. I was told that one of the tabs is likely broken and that you should contact the manufacturer, Tekonsha, for a replacement. view full answer...
The Tekonsha ZCI # 119250KIT is a passive device, that only reads the signal going through the vehicle's taillight wiring harness. It won't actually affect or interfere with those signals.
I've linked to an installation video showing the wiring harness being installed on a similar vehicle. The wire colors on your GL550 might be different than those shown in the video, but you'll get a good idea of how to identify which circuit serves which lighting function. view full answer...