Best place to tap into running lights of a truck - 2012 Tundra Double Cab SR5 w/tow

[TRover]

Installing a 2013 Four Wheel Campers Hawk onto a 2012 second gen Tundra Double Cab SR5. Need to wire the 12V, ground and running lights.



Using Attwood 7622-7 three wire kit for the connection.

12V will route via a 30A thermal fuse. 10AWG.
Ground is straight from the battery. 10AWG.

What is the best gauge to route the running lights and best place to tap? To my knowledge all shops tap into the harness going to the hitch connector. The running lights wire is in that harness. I believe there is a more effective but also more cumbersome way, to tap in the engine bay. The relay box has a number of spare ports in all vehicles. The 'switched-on acc' ports are a bit easier to locate than the running lights going to the hitch harness. But that may not be the best port.

Any hints for location, AWG and colors of wires to look for?

For example, in the engine bay fuse box there is a fuse labeled '30A tow tail'. Bussmann makes fuse adapters to tap into fuses. Could the tow tail be used for a camper's running lights?

Thank you.

 

[Rando]

Also, you may want to use a few sizes larger wire than 10AWG. I just wired my 2016 Tacoma for a FWC, and went with 6AWG, but some would suggest even going larger than that. I am not desperate for every amp from my alternator as I have solar. With 30' of 10AWG between your camper battery and the alternator, charging is going to be quite anemic.

 

[TRover]

Verkstad, for years I interfaced with my 2009 FWC via the OEM tow package connector. Turned out to be not a good method for an off-road camper because a lot of dirt and water got into the connection area over time.

This time, for the 2013 FWC, I will either tap from the engine bay or splice into the harness that goes to the tow port. For splicing, I always use water-tight heat shrink fittings. With solder.

If I find the tap in the fuse box, the connection will already be fused. If I tap into a wire in the engine bay, I would use an in-line fuse.

 

[TRover]

Rando, the FWC Hawk seems to be internally wired at 10AWG. The Attwood connector is also 10 AWG. I have a spool of 10AWG readily available. I could indeed double up the cable, but I wonder if it is needed.

The biggest current draw is the Dometic RM2354 fridge, which is rated 14.6A at 12V. The parallel setup dual Exide Edge FP-AGM24DP batteries may want to draw quite a bit if they are empty, but I suspect the charging circuitry has dampening limiters.

The cable run from the engine bay or from the tow port to the FWC input is 13-15'. Let's say 15'. Let's say worst case current draw of 30A. The alternator will be 13.8V-14.4V underway. That equates to 0.9V voltage drop, which is 6.5%. So the power management circuitry in the camper will see a minimum of 12.9V for worst case.

Per ABYC E-11 Table IV, for 10AWG, allowable amperage of outside engine spaces is 60A and inside engine spaces is 51A.

I will think about doubling vs. not doubling the 10AWG I already have. It is a good one to think thoroughly. The numbers are all good for 10AWG, but it never hurts to minimize the voltage drop. I am not convinced yet that it is needed for this setup.

 

[Rando]

The has been a lot of discussion of this over on WtW. The 10AWG wiring is a bit of problem in that is significantly throttles the charge rate to your batteries.
Unless you are using a really good chassis ground where the camper hooks up, you do have to worry about voltage drop on both the positive and negative wires - which makes the length closer to 30'. The issue is not appliances (which are not that sensitive to voltage) but charging your batteries, which are very sensitive to voltage. It is a slightly complex non-linear system - the amount of current your batteries will accept is a function of the applied voltage and the state of charge. At 12.9V, your batteries are not going to accept much current, and would take for ever to charge. The flip side to this is that because the batteries are not accepting that much current, the loss in your wire will be less and the voltage will rise, causing your batteries to accept more current, thus the non-linear nature of the problem. However, the limiting factor in this equation is the resistance between your current/voltage source (alternator) and your batteries.

Unfortunately FWC seems to use 10AWG wire for this circuit because it is cheap and easy for their dealers to install. If you are taking the time to do this right, and need your batteries to charge effectively off of your alternator, I would highly reccomend spending a few extra dollars to get larger gauge wire.