Headlight Relay Kits
So would the ones going to the lights themselves be fine?… 16 or 18ga I think ( nothing written on the wire itself….it figures…)
I would use 12ga to each power to the bulb filaments and 10ga ground. You will have no voltage drop and lights as bright as possible.
The OEMs have to take profitability into consideration so they use as small wires as possible. Smaller wire is less Cu and plastic for insulation. If they save $2 on every vehicle they build in a year, and build 500k vehicles that is $1M saved. That also is why there is no extra wire to pull things out for service. An inch or two on a harness with 20 wires × 500k vehicles. And how many terminations like that in one vehicle?
So when you do your own, go for heavier wiring. You will generally be doing yourself a favor. Now LED lights I have little experience with but generally they have lower power use for the output. You may get away with a ga size smaller, but got with the manufactrurer recommendation and maybe step up one size.
With the electronics (as compared to electrical) in vehicles these days, it is wise to get solenoids with clamping diodes built into the relay. When a circuit is opened and there is a winding in it, the collapsing magnetic field works like a small ignition coil, bumping the circuit voltage up. If this gets back to an IC you let the magic smoke out, and that can ruin your day. These relays normally have a diode depiction on them. Pretty much all new vehicles come with these so you can get good ones at the wrecker for next to nothing. Take a multimeter with you and measure the resistance between the 85 and 86 terminals both ways. The resistance one way will be a bunch lower one way than the other. This bleeds off that electrical energy harmlessly. These are sensitive to correct wiring to the 85 and 86 terminals.
