Well, here's a handy tip when around potentially "hot" electric wires; don't grab, tap, but do it with the BACK of your finger or hand -- that way if it's hot and causes your muscles to contract your hand will be pulled away from contact rather than pushed into it (Voice of Experience speaking here, vividly recalling the time I tried to stop a lawnmower engine by firmly grasping the uninsulated plug wire connection -- ripped a hole in my thumb...).
The subjectivity of How Hot? is answered by checking all the time. You will quickly learn what "normal" is under a variety of conditions, including ambient temps, road speeds and braking.
are hot, check pressures and if they are OK, then slow down. A tire with only 5 psi being towed in 4WD low-low gear will not get hot; same tire at 80 mph will not get far.
If bearings are hot, esp one side compared to other, also slow down and get to repair place to repack or replace (I make an assumption here that you have already weighed your trailer side-to-side and there's no glareing difference -- you *have* done that, haven't you?) or check brakes
to see if one is dragging or not functioning.
Quickest way to check equal brake function is to drive slow and use the control to cycle the brakes
on and off a few times. If that makes the front end of your truck try to swing to one side or the other, the brakes
aren't equal. Next step is ammeter to see current drain, which should be about 2.5 Amps per magnet (5 Amps for single axle). If drain is OK, then one side is adjusted too tight or the other is too loose; if drain is not OK, then wire is broken or magnet is NFG (polite version is Not Fine Goods).
If one bearing is REALLY hot, or you can hear grinding when your driver inches the rig forward or you jack up the wheel and spin it OR if the wheel seems a bit cockeyed, don't drive it any further or you will chance permanently damaging the axle
spindle (needing entire new axle).
Pete and Rats