Electrical question

I would like to keep my electric cooler in the car and power it from the trailer through the cars wiring.  In other words, I would like be able to plug some type of wire  into my cars wiring harness and take power from the trailer to run this cooler from my car's outlet.  Have solar panels on the trailer, so have plenty of power.  The cooler is very heavy, and moving it back and forth is a chore.  Put a very heavy duty battery in the car, but still runs the battery down overnight.  
Yes, the car has a battery isolator on it.  Thought about running a wire through the wiring harness, but don't quite know how to go about it.         ANY IDEAS OUT THERE?

I am not sure why you run a thermo-electric cooler when you have a refer in your TM.

Your thermo-electric cooler will draw at least 4 amps.  A 80amp-hour battery would be flattened in 20hrs -- probably less.  And you should avoid deep cycling any lead-acid battery.

You are going to have problems to run this cooler like you wish without an AC power source.  Your solar panels don't have enough power to run your cooler either.

I did run in to one fellow who did what you suggest. He had LOTS of solar panels and even cooked with the elecricity. If you have enough power to run your cooler I would run  seperate electric lines and stay out of the existing harnesses. Be sure to fuse both sides of anything you add in at the power source.

Check on the web--

Solar panel 2' x 4' costs $400 and will produce 4-5 amps while facing a bright sun.

Not too attractive or practical if propane is available.