Amps Out at 7Way Charge Line on a 2019 Tacoma B

It's a 30A fuse, in the engine compartment if memory serves me, check to see if that is blown.
If your RV does not have a battery isolation/charging controller built in for it's battery, a dead/low battery on the RV can blow that fuse real quick.
i.e. depends on the CCA (cold cranking amps of the truck battery) and the charging rate and state of the trailer battery.
Our electrical friends here can calculate the amperage, based on the wire gauge and the internal resistances of the batteries based on standard fault calculations. But requires a lot more info/measurements to give you a semi-accurate answer.... can safely say that it will be easily over 100 amps surge until the batteries "equalize".... that's why Jumper cables are so big!

Most RV fridges run at 2-4 amp/hrs when running.
7-14A for an instant when it starts up.
Since it's DC you'll have to use an Ammeter in series with your fridge and trailer circuit to take a reading.
As the voltage gets lower the amperage will go higher.
Check the voltage at your 7 way pin.
Check for contamination/corrosion on the connectors.


Battery's are advertised with CCA (cold cranking amps), (how much amperage it can "dump" instantaneously when fully charged at room temperature)
but for RV's and boats you also have to consider (and it's harder to find) is the A/h of the battery (Amp/ Hours).
i.e. most car batteries range from 20-70A/h
So for easy numbers for our examples...
a Shitty fully charged car battery rated for 20A/h, and your fridge draws 2 amps (and stayed running the whole time), will only last about 10 hours....

Also a good chance your RV battery is shot,
If it's not a deep cycle battery they get sulfated real quick when you run them down on a trailer.
Pull the battery out and get it tested for free at most auto parts stores.

 

Now see pin 4? Aux12vdc +charging. This pin is is where voltage(12dc) goes to travel trailer charging circuit/battery. The trailer refrigerator can be set to run off it's battery. The refrigerator heater draws 11.7 amps on 12vdc. That's refrigerator speak for cooling. I have 12.8 vdc, sometimes as much as 13.2 at the pin. Without rigging up some creation in series between truck and trailer, I'm trying to find out what amount of amperage is available at this pin.

 

Thanks daks. Good info there, others should take notes. I’m new to 3rd gens, not Tacoma’s but this has me wondering. I’m familiar with electronics/electrical, I’m retired Navy electronics.
The battery is good - checked. Only thing left is determining whether charge output on 7way plug is sufficient for refrig. Will try Toyota tech again.

 

If you don't have one ask to borrow or buy a current clamp.

 

Why not ask in the towing forum?

 

Navy Electronics...
Lol you'll know more then the dealer techs by a factor of 100. And me as an Electrician by a factor of 50.
You must have giggled at the grade 2 battery explanation.

Unless there is some current limiting circuit besides the fuse and relay... It's just Ohms law.

Unless some of the Gurus here of the service manual can find note of a current limiting function for that, only corporate engineers would be able to answer that question.

Check your Voltage Drop at Battery, Trailer Hitch pin, trailer battery and at the fridge, with the fridge running and not running.
Might give you some clues.

Or of you have a120V inverter on the trailer hook up a hairdryer or heat gun so you can simulate a load.
or Turn on 12V lights...

Keep your eye on the voltage and keep increasing the load ... just troubleshooting a powersupply 101.

You'd probably figure it out faster that way then waiting on a dealer or Toyota.

You said you were at about 11.7A so that sounds about normal for a smaller RV fridge (150-200Watts).

So go back to basics... 12Ah for your fridge... (going back to your original question about running the battery down fast, and don't forget you can't use the whole rated Ah of lead acid batteries ... only 50-70%) and don't forget the relay in the circuit that shuts off power to the trailer charge pin when the truck is off....

 

Yes, But there are situations where the air-gap in the fuse can be bridged. High current / spike situations is probably the #1 cause. "General" plans for circuit protection like: conductor size, fuse current rating, ect, are nonexistent in a fault situation. In the AC Field, the only plan is "Instantaneous Trip Ratings". But even Circuit Breakers can be bridged. Or completely fail. I have seen for myself where certain Current Spikes have successfully bridged the gaps of lower class protection devices until it finally reached a system that was robust enough to clear the fault. .

Ok it's established that I'm not an automotive electrician. But I have enough knowledge to know that something else has to be going on. According to the OP's post, he has 2 different batteries at different levels of charge. 1) the tow battery. And 2) The trailer Battery

A) It's physically impossible to have 2 batteries "bolted" to exist at different levels of charge.

B) The associated wiring (both tow vehicle and trailer) can not be the limiting factor. Yes, the wiring imposes a value of resistance. But, at their limits, they will also build "heat". Then you would have a bigger problem.

Those are the two reason why I say that something else has to be going on here. (like a regulator).

 

If it has a 40 Amp fuse protecting this circuit, The math is quite simple: 40A * ~12V = 480W -----BUT -----There has to be something regulating the charge. (Trailer Fridge @ 11.7A only equals 140.4 watts).

If the charge isn't regulated, it could easily exceed the current rating on the tow vehicle.

Edit: Just thought of something else - You can't charge a battery @ 40 amps. You would probably damage the battery charging it a 10 amps.