The SLT (non-sport) trucks use the 9004L headlamp bulbs. IMHA the wiring involved in the headlamp circuits suck. For one thing, the wire is a whopping 18 AWG. Seems a little wimpy to me. Also, as with most of the newer vehicles the headlamps are “low-side switched”. Meaning that the bulbs are connected to 12V all the time and the headlamp/high beam/low beam switch switches the ground connection. This is done because it’s cheaper to design solid state “low-side switches” than it is “high-side switches”. The problem it presents is that there is essentially double the length of wire. The entire headlamp circuit consists of a 15 amp fuse with a wire running to the “common terminal” of the headlamp, then another wire running to the high/low switch, then another wire running to the light switch, then another wire running to the grounding point. This circuit is duplicated for the high beam and the low beam circuits. On the older “high-side” switched lights, there was a short length of wire running from the “common” terminal of the headlamp to ground and then a wire going from each filament (high-beam and low-beam) to the switches and then to the fuses. There were also relays included in the circuit to avoid having to run long lengths of high current wire. This also saved having to run long ground wiring.

I wanted to improve on this wiring in order to eliminate switching the high current loads and also to eliminate the lossy 18 AWG wire. This could have been accomplished with one relay in each circuit (high beam and low beam) but I used a total of four relays, two on the left headlamp and two on the right. I found that a good place to mount the relays was on the outside of the front vertical surface of the battery boxes. I drilled two holes and mounted them using #10 stainless hardware. There are some options that can be taken when doing the wiring. One option is to use new 9004 sockets with pigtail wires. This is a recommended option, especially if you are considering increasing the wattage of the lamps. The stock 9004 sockets are barely strong enough to handle the 65W/45W lamps. If you go to 100W/80W as I did, heavier sockets are in order. They can be purchased from various sources.

This conversion requires cutting and connecting of several wires. If you aren’t confident in your abilities, stop right here! A schematic is included. Grounding points are available under existing ground connection screws on both sides of the vehicle on the inner fenders.

If there is anything you don’t understand or anything I have left out, please feel free to PM me. Mine works great. I’ve got brighter lights and what I feel is a more reliable and stronger headlight circuit.

Happy wiring!

Gary

 

There aint anything wrong with having brighter headlights is there??. I may have to try that when Im feeling ambitous (or can find the time). Well done ;D