Wiring relays

YES, very important to fuse both ends of the + wire going back from the relay. Smart to also have a disconnect switch. You never want to see a short out or kill any or all of your batteries. With high amperage of battery DC, shorting can quickly cause a fire and your vehicle has lots of fuel that burns real hot and fast. Sure don't want the RV to look like charcoal either! It has propane that goes BOOM! But only once each toasting occurrence!

I don't agree with using the vehicle's body/frame for very high amperage flow. Too much resistance on the - side. I run both + and - no 2 copper fine strand gauge cables or a min of no 4 gauge copper fine strand cables between batteries. Smooth efficient reliable full current flow! There's very high amperage involved! No "choking" occurs using both cables which can or does happen with high current flow thru steel in distance with high amperage 6 or 12 volt DC. Why not get as much of the current delivered from point to point as you can reasonably? Efficiency!

I use exterior rubber coated welder cables covered with the split corrugated plastic sheathing that's insanely cheap and keeps the elements from rotting the rubber over time. These cables run under the truck back to and up thru the bed thru thick rubber protection grommets. The cables run along the frame and are very securely attached to the frame etc with lots of heavy cable ties so they stay there. The fine strand allows flexing which occurs when driving without wire breaking from flexing fatigue like heavy gauge strand wire is known for.

Bedlam wrote:
.............Since you plan to to connect to your trailer batteries, use the same type of heavy circuit breaker from the positive camper battery to heavy gauge wire and second heavy gauge wire connected to the trailer frame for ground into the same type of Anderson connector at the trailer tongue.

This is important to do. You will have a high energy source at each end of the wire so each end needs protection. This is different from a typical circuit with the source on one end and a load on the other.

I've been using the starter solenoid relay for battery isolation and charging on all my tow used vehicles since 1984. Never purchased an off the shelf battery isolator since as that's all they are is a relay at big cost. Installed a 65-8- amp slide switch and a 65-80amp marine fuse before the relay and a 65-80 amp marine fuse on the other end in back of the truck.

Last 2 trucks I also added a lighted on-off control switch next to the RV brake controller under the I/P so I can even control it while driving if desired. The vehicle ignition switch activates the relay instantly when turned on with the key and turns the system off when turning the ignition off. Cheap, very heavy duty, easy to do, and 100% positive!

Have a no. 14 gauge wire with an alligator clip on each end to activate the relay by attaching to a battery + terminal and the + on the relay which couples the 2 group 31 deep cycle batteries (all batteries are except the 2 engine batteries) in the truck's driver's side bed. Or if the TC or 5th wheel is connected with their batteries also, I can easily start the truck's diesel engine anytime or use a 1500 watt + inverter outside right from the truck for a long high wattage draw without even needing to run the truck engine. Couples up to 9 big 12V batteries and the connecting wire cables are no 2 gauge fine strand copper welder wire. 2 batteries in the engine compartment, 2 in the bed, and 5 in the 5th wheel =9. 1 in the TC, 2 in the truck bed, and the 2 for the engine = 5 in that configuration.

Ordered my truck with dual alternators which makes very quick work of recharging batteries if or when needed and because of the very heavy gauge coupling cables used. Little voltage drop!

The OP is doing the smart thing and approach!

enblethen wrote:
Here is wiring diagram from Tekonsha
Wiring diagram

This is what i was looking for, thank you very much. The diagrams i found on google showed the smaller relays and they had 5 pins which didn't look like they would work with heavier gauge wire very well.

You can find an ignition controlled fuse and tap it to control the relay. Just ground one of the little posts and run the fuse tap to the other. Absolutely put a fuse or circuit breaker near the battery for safety.

Excellent diagram Bud.

wing_zealot wrote:

rhagfo wrote:

wing_zealot wrote:
Why are you using a relay? Just put a switch in the line.

Well because you can only run so much on a circuit before you over load a switch.

Take my Backup lights.
I have halogen backup light on both my TV and 5er! If I tried to run all six of my backup off of the stock backup circuit for power I would be blowing fuses all the time. Instead both sets are on relays, and grab power for a large circuit.

I get all that, but you don't need a relay to operate those lights, all you need is a large circuit with a switch of the proper size in it to operate the lights. Only difference being they don't come on automatically with the backup lights. They come on when you "need" them with a switch. To each his own I guess.

Well the way I wired, both signal and power were very close, so I didn't need to run wires the full length of the TV.
Can't think of a time I don't need backup lights when backing up. :h

Need at night to see, and day time to warn the jerk behind me I am backing up. :B

I don't need a ton of switches, in the cab, and with a switch, might leave on by accident.

Run a large circuit breaker off the positive battery post to a constant duty solenoid (type of relay). The solenoid can be switched on and off by your ignition circuit or a dedicated switch. From the output for the solenoid, run a heavy gauge wire to the rear of your truck and at the rear run a second heavy wire off the frame for ground. Using an Anderson connector, you will now have a high amperage power point that can be plugged in to your trailer for better charging, power a receiver mounted winch or even be used as connection for jump starting other vehicles.

Since you plan to to connect to your trailer batteries, use the same type of heavy circuit breaker from the positive camper battery to heavy gauge wire and second heavy gauge wire connected to the trailer frame for ground into the same type of Anderson connector at the trailer tongue.

You should be switching the positive and not the negative. The negative can us the frame as the conductor.
Are you wanting to switch power for battery charging?

rhagfo wrote:

wing_zealot wrote:
Why are you using a relay? Just put a switch in the line.

Well because you can only run so much on a circuit before you over load a switch.

Take my Backup lights.
I have halogen backup light on both my TV and 5er! If I tried to run all six of my backup off of the stock backup circuit for power I would be blowing fuses all the time. Instead both sets are on relays, and grab power for a large circuit.

I get all that, but you don't need a relay to operate those lights, all you need is a large circuit with a switch of the proper size in it to operate the lights. Only difference being they don't come on automatically with the backup lights. They come on when you "need" them with a switch. To each his own I guess.