Light Booster
More Light for GM's 1990-current Vans & Light-Trucks

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By Jim Bigley

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Here in the northern latitudes during the winter months, we spend a lot of time driving to and from work in the dark, and I appreciate all of the illumination a good set of headlamps can deliver. To improve night driving, Diesel Services Group began offering a performance headlamp wiring kit for GM vans and light-trucks (equipped with 9005 (HB3) and 9006 (HB4) bulbs) that provides a significant improvement in headlamp intensity.

The new Light Booster wiring harness kit is a quality product, and includes components such as OEM electrical connectors, Bosch relays (designed specifically for a lamp load circuit) and phosphor bronze terminals using the recommended crimping methods. The wiring harnesses are complete with all connectors installed, and installation requires only about 20-30 minutes using simple hand tools. We're told that all Light Booster harnesses are quality and function tested before leaving the manufacturing plant in Sweden.

I began the harness installation by removing the composite lens assemblies. This is accomplished by removing the lens hold-down studs (as indicated in the photo) using a 5mm nut driver. Once the studs are removed, the composite lens can be brought forward through the opening. There may be some interference with a portion of the grille, but a careful application of a screwdriver will help you guide the composite lens out.

The grille doesn't have to be removed to install this harness assembly.

Once the driver's side composite lens is removed, you can route the longer ends of the new harness through the opening in the radiator partition from behind the battery. I didn't need to remove the battery for my installation.

The original lamp connectors are plugged into the new harness, matching the color-coded wires. The original lamp wiring will now be used to activate the new Bosch relays, while the heavy-duty relays will connect the batteries to the lamps through much heavier wiring.

You can see in the above image that I routed the longer end of the new harness (destined for the passenger side headlamp) down through the hole in the bumper. From there, I ran the new wiring back inside the bumper opening against the radiator partition, then over to the other hole in the bumper. Next, I routed the wiring up into the opening where the passenger side composite lens had been. This took only a few minutes. The holes in the bumper made this step a snap to complete.

Once the wiring is roughly into position, you can mount the new Bosch relays to the upright radiator partition support using the supplied double-stick tape. For GM diesel trucks, you should install the relay end of the harness on the driver's side. I cleaned the painted upright radiator support with the supplied VHB cleaner to be sure the tape would adhere well.

The battery connections can now be made using the generous lengths of the new power leads. I wrapped the ground and positive leads around the appropriate ends of the battery, then installed the harness terminals using the brass battery terminal adapters supplied with the kit. To prevent corrosion, I smeared a little battery grease on all the new connections.

The original headlamp wiring harness uses too small a wire gauge to allow the lamps to develop full intensity. The original factory lamp wiring used by GM is 16 gauge and in some cases even the smaller 18 gauge. This produces a 1-2 vdc voltage drop to the bulbs, which reduces headlamp intensity. The new performance headlamp harness uses 2-½ square mil (~13 gauge) wire for all the shorter runs, and 4 square mil (~11 gauge) wire for the longer run to the high-beam lamp on the off side (green/black pair). (Note: The wire size to the low beam relay is 4 square mil wire (11 AWG) and 6 square mil wire size (9 AWG) to the high beam relay. 4+6 = 10 square mil (7 AWG) relay feed.)

The Light Booster harness wiring makes a closed loop with the battery, instead of using the chassis as a ground return. Using the chassis for a ground return can result in a less reliable electrical current path. An alternative connection for the relay feed would be the alternator, but we're told a reduced service life of the bulbs could result.

The original headlamp wiring is nearly 20 feet in length, when you consider that power comes into the cab to the light switch, then forward to the driver's side of the grille, then across the grille to the passenger side. This round trip requires a nearly equal length ground wire, which combines to create a voltage loss that reduces lamp intensity. Aside from using much larger wire gauge, the new performance lamp harness is also considerably shorter. Heavier wire and short runs help deliver full battery/alternator voltage to the headlamps, with minimal voltage loss.

These harnesses are capable of handling the high intensity 9005 (HB3) rated at 100W, with no lamp temperature problems. (Note: Low voltage generates more infrared light (heat) and less visible light.) Diesel Services Group can help you select high performance replacement halogen/xenon filled lamps (where legal, capable of producing up to 50% more light than standard lamps).

This harness allows the low-beam lamps to remain on with the high-beam lamps (if you wish), producing a much wider and brighter illumination pattern. This is accomplished with the use of a diode plugged into the green and brown wire terminals of the original (and now unused) off-side lamp connectors. As indicated in the photo, the banded side of the diode is installed toward the gray connector. On the 1999-2002 (current body style trucks & SUV's with yellow/pink bulb wiring), the diode should be installed in the opposite orientation between the matching black wires of each connector.

The image on the left shows the diode installed without the clear tubing, so you can see the diode and color coded wires more clearly. The image on the right shows the completed installation with the clear tubing. While the plastic tubing is a pretty tight fit, I would recommend a good wrap of electrical tape over the length of the assembly to make certain this connection doesn't come loose.

The diode activates the low-beam Bosch relay incorporated in the new harness, when high-beam is selected. Combined with two 100-watt high-beam lamps, running all four lamps brings the total to 310 watts of illumination (when using legal 55-watt low-beam lamps), and virtually eliminates the need for any auxiliary bumper mounted lights. The total headlamp current draw is about 22 amps in this configuration, and is easily handled by the stock 105-amp alternator.

Having a brighter set of headlamps may require a slight adjustment in aiming the lenses to reduce glare to an oncoming driver. The factory lens alignment may not be low enough to prevent others from "flicking" their lights at you when using performance lighting.

Seeing is believing! The comparison photo on the left was taken after installing new Philips 55-watt low-beam lamps in both the driver's and passenger side. The driver's side is being powered by the new harness, while the passenger side is still powered by the original wiring. There is a big difference in lamp intensity. This picture was taken with the engine off.

Dr. Lee Swanger says: "This photo comparison understates the difference in brightness between the two headlamps. This is because only about one/half the required current is now going through the restrictive original wiring, so the voltage drop to the passenger-side headlamp is only one/half of what it was originally. The passenger-side lamp in this photo is therefore not as dim as it would have been if the driver's side headlamp was also being powered by the original harness. The difference in headlamp brightness before and after is actually about twice what the photo depicts."

The new high-output lamps and Light Booster harness make night-driving a totally new experience. Believe me, no one will want to have a "light fight" with this truck! Please contact Diesel Services Group (see below) for more information.

TDP