I have Absolutely used plenty of trailers without lights during the daytime. Truck tail lights are still visible, and regardless, you are still suppost to maintain follow distance. Its not like anyone uses turn signals anyways, so they are a non factorI'll probably regret saying this but I've been known to pull light trailers in daylight with no taillights, if my truck lights are easkly visible.
I've burned up 7-pin connectors, but oddly enough, never a 4-pin flat! But that's due more to application than connector reliability alone.Fortunately I've never had problems with a 7 blade round wiring coupler.
I blew a fuse on my RV once using a seven blade with the Bluetooth curt echo brake controller only time Ive had a problem with 7 blades. My RV doesn't have a integrated brake controller and the micro toyhauler had electric brakes I was pulling also had a house battery charging thru the 7 blade plus it was powering up the echo I guess. I opened up a 4 flat once to see why it failed even though the outer casing looked good the wire on the inside was corroded severely where it made contact with the prongs.I've burned up 7-pin connectors, but oddly enough, never a 4-pin flat! But that's due more to application than connector reliability alone.
I'm usually towing a trailer with rechargable batteries when using the 7-pin, and those chargers pull something near 20A continuous, so any dirty or loose contact will heat up and melt the housing around it.
The 4-pin flats are never handling more than a few brake lights and marker lights. The markers pull relaitvely little current, and the brake and blinkers are intermittent duty only.
I see that on occasion. More often though, they turn them on after starting the turn.With that, id rather people not use turn signals at all, rather than turn them on half a mile before a turn