Im looking to add a 40amp relay to a 40amp circuit under the hood for so me lights, and every relay harness I find has pigtails with 12g wire. Shouldn't 40 amps require 8g wire?
I've searched high and low and cannot find a way to attach 8g wire to a 40amp relay, short of soldering it straight to the relay.
Even 80 amp relays have 12g wire on the harness's I've found. This is bugging me....lol
I have had the same issue when looking for large relays. By the book, a full 40 amp load would require min. 6 gauge copper wire, and that would be good for a total length of 20 feet to maintain a voltage drop of less than 3% (.36 Volts) Much of the accessory industry greatly undersizes wire size and switches etc. Often they are also using CCA (copper clad aluminum) wire which has a lower rating than full copper. the heat generated by overloading the wire causes failure. Keeping wiring as short as possible and making good connections is critical. First thing is to know exactly what amperage your load will be drawing. Lighting, especially LED draws much less than it used to. Check specifications for each item to be connected, you can also connect an amp meter in line and test the lamp if you do not have specs. 40 amps seems high for lighting. a 40 amp load will also make a good hit on your alternator when totaled in along with all other vehicle loads, so make sure the total load of the vehicle and added accessories is within capacity of your alternator. If you have more than one light that you want to control from one switch and the amperage of each lamp is high, consider adding a relay for each light, that will bring down the load on the relay and associated wiring to within specs of a smaller rely and its socket wiring. the relay triggers draw a tiny amount and can be gathered to one standard switch for control.
For plug in relays and connectors, the largest one I could find was this one from Amazon
The three large wires (input, normal open and normal closed) are not listed by size, but the ones I received measure out averaging 0.10 inches in diameter for the conductor. This equates to 10 gauge and looks to be all copper, one step up from most others I have found. (the wire would be rated at 20 amps) The relay is stamped at 80 amps (greatly overstated in my opinion). I have been using these to control the power supply to all my two way radios so I can shut them down with one switch. As the highest load passing through when transmitting is a bit less than 30 amps and is it is a non continuous load I have not seen any issues of warm wire or anything.
