12v cooler

And that could depend on the brand of truck. I had the same problem in a ProStar, but not in a Cascadia. It was always with the Coleman cooler.
Perhaps the wiring is thinner on some trucks, or they use cheaper sockets?

And here is a hint to use less power and keep things cooler... Place a one inch layer of Styrofoam between the floor and cooler.
It isn't all about ambient temp. The floor can get quite warm when idling and during drive time. Insulating the bottom of the cooler removes a huge heat source.

 

Only problem i had with the Igloo 40 QT coolers was the little fan motor. Always seemed to last about 18 months then they squeal and freeze up. I carried a replacement fan motor in the truck so i could immediately replace it. The little motors were fairly cheap.

 

If you have one of these thermoelectric units, keep it directly off the floor. Put some sort of spacer/insulator under it. At least 3 inches will work well.

 

I easily spent far more on replacement power cords for the coleman and igloo 12 v coolers than the price of the 2 coolers I bought over the years. IMO, if I could get 2 months from a single power cord before it melted, I felt lucky. I would only use a 12v thermoelectric cooler until the 12v compressor cooler or fridge arrived to replace it. I had a wireless thermometer in mine and the temp display on the truck dashboard so I could see the moment it stopped working and replace the power cord at the next on-ramp.

 

and keep the fan vents clean. they suck up dust and crap.

I used the cheap ones for years, never paid more than about 20-30 bucks every yrs to yr and a half.

used my fuel points

 

Just go get a refrigerator. You can get a BougeRV 42qt for about $250. Get a refrigerator/ freezer for $350. Mine have thousands of hours bouncing around in the back of 4x4's

 

And a real refrigerator will draw a LOT less power and keep your food MUCH colder than those useless Igloo or Coleman thermoelectric "coolers".