4 Hi Headlight Mod

[MinnesotaChevy]

This is a good write up, wish I had seen it beforehand. A buddy just purchased a '99 Tahoe and wanted better illumination. It had been a while since I did this on my own truck so I pieced together how we did it.

Time Estimate:

20 minutes

Materials: (about $12)
1. 1 Relay (with plug-in harness, optional). Relay has 4/5 prongs, with #85, #86, #87 and #30 terminals. These are very common relays for cars. I used a spare SPDT relay & harness that has a fifth terminal (87a) that is not used for this project
2. 3-4 feet 16 gauge wire
3. Flexible Wire Conduit
4. Solderless wire connecters
5. Ring terminals for power and ground
6. Shrink wrap
7. 1 inline fuse

Step 1
Disconnect the battery

Step 2
Look for the wiring bundle inside flexible conduit on the driver’s side fender well near the ABS system. Open the conduit and find the brown and lime green colored wires.

Step 3
T- Connect the vehicle’s brown wire to terminal 87 of the relay

Step 4
T- Connect the vehicle’s lime green wire to terminal 86 of the relay

Step 5
Connect a ground wire to the fender well (there are several existing bolts that you can leverage for ground) and connect it to terminal 85 of the relay

Step 6
Connect an in-line fuse / power wire to terminal 30 of the relay. Use your choice of power source (the underhood relay / fuse block is 12 inches away from where we spliced into the headlight wires on the driver’s side wheel well towards the firewall - we chose to tap the battery power supply to the fuse block)

Tape / shrink wrap all connections and hook the battery back up. You now have 4-high!

Other Stuff:
WIRES FOR SPDT RELAY HARNESS (optional- these were the wire colors on the harness that corresponded to the terminals on the relay- you can just match your wires to the terminal numbers on the relay using female solderless connectors):

30 BLUE fused power source
86 BLACK high beam wire- lime green in OBS trucks
85 WHITE ground to vehicle body
87 YELLOW low beam wire- brown in OBS trucks
87a RED (BLANK for this project)

SPDT Relay: (Single Pole Double Throw Relay) an electromagnetic switch, consisting of a coil (terminals 85 & 86), 1 common terminal (30), 1 normally closed terminal (87a), and one normally open terminal (87).

When the coil of the relay is at rest (not energized), the common terminal (30) and the normally closed terminal (87a) have continuity. When the coil is energized, the common terminal (30) and the normally open terminal (87) have continuity.

For this application, the high beam circuit is activating the relay’s coil and closing the 30 – 87 circuit in the relay sending power to the low beam lamps. Once the high beams are turned off the coil is de-energized and the low beam circuit operates normally.

wait so is that the only place I have to splice the wires because Ginger recommends to splice in right before the lamp

 

[MinnesotaChevy]

wait so is that the only place I have to splice the wires because Ginger recommends to splice in right before the lamp

Nvm I was to impatient and and now I too have 4 hi and I am completely happy with it

 

[Evatyl14]

Allright so I left my day time running light fuze in, so my daytime running lights work, and I did the 4-hi mod. and everything works, the daytimes and the 4-hi. So, someone said to disable the daytimes, but will it harm anything if I leave them as they are?

 

[MrCTS]

I love this writeup. I was too afraid to do it myself and ended up grabbing the setup from JCWhitney. I'm very skiddish when it comes to doing a mod on my own stuff then it looking like poo or performing like poo

 

[95C1500]

I was afraid too, but one of the easiest things I'v ever done to my truck

 

[98-Z71]

Okay, so instead of running the power from the battery to the relay I can tap into a 12 volt auxiliary post in the fuse box that's only hot with the ignition on and run power from there right? What amp fuse and wire should I be using for the power? Something thicker than the 16 gauge? Just not very familiar with wiring specs.

 

[Hunttman01]

Okay, so instead of running the power from the battery to the relay I can tap into a 12 volt auxiliary post in the fuse box that's only hot with the ignition on and run power from there right? What amp fuse and wire should I be using for the power? Something thicker than the 16 gauge? Just not very familiar with wiring specs.

That's how mines wired. I have a 30 amp fuse for the post. Don't remember what size wire

 

[glendayle]

16 gauge should be fine. I usually use 14 ga, but 16 or better should be just fine for lighting and relays.

 

[bigdaddy51200]

Written up by GoCougs

OK I did the mod today and absoultly love it.]

Thanks for the write up . I completed this mod today and it was very easy to do.

 

[Jeremyc]

Going to try this tomorrow and see how it goes.