These instructions guide you in installing a single relay to control the headlight power to the dimmer switch, from the dimmer switch to the headlights. Due to popular demand, an alternate set of instructions are also available with drawings that detail the process for installing 2 relays that would be controlled/activated by the dimmer switch and pass power directly to the headlights.
The other set of instructions can be used for stock setups also, but is designed for those who want to go above and beyond for their lighting; rack lighting, Hella lights, powerful halogen lighting, multiple bulbs, etc -- or, for those who want to keep their options open for future lighting power.
My goal in rewiring my rig was to keep it pretty close to stock, and reduce the fire danger. I wasn't after additional lighting, I just wanted what was originally there to work as well as possible. As I was peering into the wiring harness during the planning phase rewiring my entire rig, I tried to balance the amperage needs of the new headlights with trying to keep the job simple but effective.
If you are not sure which way to go, then go with the dual relay setup -- better safe than sorry. And when it comes time to make the decision on additional lighting you will know how to correctly plug it into your setup.
Steps 7, 8 & 11 are really the only differences between the 2 sets of instructions. If you do decide to start with single relay you can easily upgrade to the dual set later on, so you havn't worked yourself into a corner.
Whichever way you go your wiring will be much safer, but do one or the other - its easy.
v1.03 3/21/01 - added link for dual relay installation instructions and images
v1.02 3/17/01 - added TOC, note to install fuses in step 10, note to install headlight switch back into dash in step 10
v1.01 1/29/01 - added drill and bit to tools, shortcut link to schematic, fixed hideous spelling mistakes
v1.00 1/27/01 - posted
*Please*, don't look at the length of this and say to yourself "dang, this looks like a lot of work" and then bail out from doing the upgrade, its really not a lot of work. I've just tried to be a narrative as possible so thats why this document has become so long. Its really pretty simple, and you end up with incredibly bright lights and a much safer rig and reduced the fire danger from bad wiring in the lighting circuit. 90% of the work involved is spent identifying the existing headlight wiring, and making sure that it has no problems. This is all outlined in step 2.
If you want to shortcut all the narrative and just want to see the diagram with some notes on how to do it click here, you can always refer back to these notes later if you run into trouble in a certain spot.
All drawings of connectors that are shown below are viewed looking directly into the connectors, i.e. if you were to remove the connectors from the dimmer switch and hold it in you hand the image is shown looking into the front of the plug and the wires would be coming out of the back, non-visible, side.
If a large spark is seen when you disconnect the red/positive/+ lead from the battery - stop here. You have a short somewhere in your wiring that needs to be identified and fixed before proceeding.
We are going to use some existing wiring to help speed the installation up. We are going to use the circuit from the dimmer switch all the way to the headlight bulbs. But, we are going to read the circuit in 2 steps to make sure that the wires are in great shape before we use them, this will help isolate and resolve any problems that may exist. Use the resistance settings on your multi-meter to read between the connector block and the headlight plugs on both the right and the left headlight. Do them one at a time, i.e. read the connector block to the left plug. Once that reads correctly then read the connector block to the right plug. Do this for both the high beam and low beam circuits. Then we will read between the dimmer switch and the connector block
Move your meter to the lowest resistance setting (mine was labeled R x 1) and zero the meter. To zero the meter, connect the + and - leads together, find the adjustment wheel, and move the needle/display until it reads 0. The zero position in also known as the open position.
battery is still disconnected, right?
Starting with the left headlight plug, read pin 1 (hi beam) to connector block stud hi beam checking for zero/open. It should read open, if you get a closed reading you need to replace the wiring or the plug. Open means that there is a connection between the 2 points. If you are using an analog meter the needle should swing from the closed (or infinite resistance) side to the open side. If you are using a digital meter then it should read 0. Use the lowest resistance setting you can, but even at the highest setting the needle should move (analog meter) or the gauge should read 0 (digital). If you have problems here be sure to do a visual first before panicking. Is the wire cut somewhere as it comes thru the grill? Are the connectors corroded? Is the plug decayed? Try reading the connector from the back of the plug to make sure you have a good connection. Now, read pin 2 (lo beam) to connector block stud lo beam checking for zero/open. read pin 3 (ground) to a bare metal spot on the body somewhere. Resolve any issues before moving on.
Once all the readings are correct, move to the right headlight
Now this one is a bit trickier, but only because they are pretty far away from each other. We are going to read from the output of the dimmer switch to the connector block. Pull the carpet back and disconnect the plug from the dimmer switch. Read the hi beam circuit - between the hi beam/right lug on the connector block and pin 1 on the dimmer connector checking for zero/open. Since your meter leads probably won't reach between these 2 spots use some additional wire on your leads to help reach the 2 spots. I made a small "extension cord" with about 8 ft of wire and an alligator clip on each end to help out on these types of distances. Read the lo beam circuit - between the lo beam/center lug on the connector block and pin 2 on the dimmer connector checking for zero/open. Resolve any issues before moving on.
this will help us identify where we can patch in to the main power feed for the headlights. remove the headlight switch by first removing the knob from the switch. Reach under the dash and push the pin/button on the bottom of the headlight switch in as far as you can and then pull out on the switch. The knob and pin should come right out, but this can be tricky. Using a small flat blade screwdriver, spin the inner ring so that it loosens and the switch should come out. Ok, after looking at the pin identifiers on the switch, read between the H connector on the headlight plug and the power input on the dimmer switch checking for zero/open. I believe that the wire on my truck coming off the H connector was yellow, but as always with any jeep yours may be different. The switch has the letter H marked on the plastic, be sure to match that up with the correct wire on the plug when you read the circuit.
Resolve any incomplete circuits before moving on. If you can't figure out what the issue is that is causing the problem then replace the bad wires with new ones. Use #10 gauge wire as a replacement, and try to match wire colors on the wires that you are replacing to make troubleshooting easier later. To help you identify replaced wires, cut the connectors off each end and place a tie-wrap snugly around each end of the wire. Later on if you see a single wire with a tie-wrap on a wire you know it should be dead.
Remember, if you find any problems here you will have problems later once we try to fire the lights up later on. Once you get zero/open readings all the way thru move to step 3
OK, the hard work is over. If you have made it this far, then you have seen all the wires that affect the headlights ability to put out light, and we know that they are good. This will help you troubleshoot any problems that come up later after we are done. Now on to the cleaning and mounting phases.
Use the 400 grit paper to clean your connections on the connection block. This will help ensure that any crud built up over the years will not cause the power to drop as it move towards the lights. Any power drop, no matter how slight, will significantly reduce the amount of light your headlights put out, our goal here is for minimal, if any, power loss.
Use a 3/8 wrench to remove the nuts ONE AT A TIME from the connectors being careful to put them in a safe spot where they will not be disturbed and you won't forget where they are. You have 5 things to clean using the sandpaper. 1) clean the stud/post till the crud is removed, don't sand it too far down and affect the threads. 2) Clean the bottom of the nut. 3) Find the 2 wires that route down to the grill and clean both of the round eye connectors. 4) Find the wire that comes from the passenger compartment and clean the round eye connector. 5) clean the washer. Put the nut back on and tighten it down.
Repeat for the other 2 posts. Even though there are only 2 connectors for the headlights, do all 3 this way - one at a time. The 3rd connector is for your parking lights in the front, cleaning the connectors for the parking lights may help make them brighter (it won't help for the blinker circuit, those are different wires)
Install those brand-spankin' new Sylvania XV bulbs into the plug. Install the retaining ring and screws. Install the bezel. Repeat for the other headlight
Remove the 2 large phillips screws holding the dimmer switch to the floorboards and install the new switch. Reattach the dimmer connector plug.
Find a spot on your inside firewall to install the new fuse box. I found that since I don't have a clutch, the spot on the firewall to the left of the brake pedal was a good spot. I would not recommend putting the fuse box in the engine compartment, getting water in fuse box could cause problems. Do not install the fuses yet, let's get it wired up first. Locate the power input for the fuse block and identify a power out circuit for the lights and another the switch.
I located my relay right above the fuse box, I also stuck a piece of rubber from a bicycle tube behind the relay to make sure that there would be no possibility of shorting the wires out to the body. Drill a hole in the firewall and thread the screw into the metal. You might want to leave the relay out until we go to hook it up, the connections can be hard to see.
Coming down to the end of this, be sure to take your time here
HOWEVER, do not stop here - these headlight switches are not designed to handle the power requirements of the new bulbs that you put in. You will smoke the switch and may light your cherished waggie on fire if you do not install the relay in the next step!
Essentially what you have done is installed large current sucking devices (headlights) that are still connected to the switch, and have fed the switch with a huge amount of possible power (30 amp line direct from the battery). The switch is the weak sister, it will attempt to pass in all the power as it overheats and starts to smoke and burn.
Connect the 30 amp fuse into the socket that you identified earlier as the 30 amp line. safely string a 10 gauge wire from the 30 amp fuse box output to the connector marked "30" on the relay using a spade lug on the relay end of the wire. This is you 30 amp power that will be delivered to the headlights when the relay is turned on. Put a spade lug on the end of a 10 gauge wire, and run it from relay connector "85" to ground, use the small round eye connector on the ground end. This provides a relay ground.
ok, we now have power to both the relay and the switch, now we need to have the headlight switch activate the relay AND get the 30 amp power out of the relay and into the dimmer switch on its way to the headlights.
Take the wire on the headlight switch connector marked H that we used our meter on before in Step 2 - checking the power feed and snip it in two. Take the wire from H and splice on enough wire and a connector to attach it to relay connector "86". this turns the relay on and off when the headlight power switch is pulled in and out. Run the other side of the wire that we just snipped to relay connector "87", this feeds the 30 amp circuit into the wire that goes to the dimmer switch.
if you have not already done so, attach the relay to the firewall making sure that all wires and connections are safely protected. All other wires connected securely? Wires cut to length? No iffy connectors still attached? Wirenut on the old headlight power feed? Knock any non-headlight wires loose that need to be reattached/reconnected?
Reinstall the headlight knob into the switch, this will be temporary until we check things out. Once everything checks out then we will reinstall the switch permanently. Be sure that the modular connector is attached back on the top of the headlight switch.
you've done the following, right??
OK, first off - use some sense here. If something bad seems to be happening, disconnect the battery and resolve the issue. With that said...
Install the fuses into the fuse block
Connect the battery terminal keeping an eye out for large sparking when the terminal touches the battery post.
If all is ok, then proceed
capture the moment
lights - oooohhh, ahhhh! or ahhhh, crap! ??
the moment of truth - pull the headlight switch out so that the lights go on
for those with "oooohhh, ahhhh!" be sure to test both hi and lo beams, make sure the front parking lights are working as well since we cleaned those connectors. Install headlight switch back into the dash
for you "ahhhh, crap!" folks, don't despair, lets figure out whats going on.
OK, you know where the wires are, so lets start at the beginning, take a breath and turn brain on...:
Assuming that there is no sparking when you hook the battery back up, and neither headlight is working check the following in this order:
If one headlight is working and not the other
Well, today I bought a new Sylvania H6024XV light to replace a broken one on my truck, so I devised a quick experiment.
I hooked up the lamp to an adjustable power supply so I could apply any voltage I want to it and monitor it with a DVM. I taped a white card to the wall and pointed the headlamp at the card from a distance of 8'. Then I mounted a Sekonic incident light meter on a tripod so I could read the brightness of the light reflected from the card. Took a few data points at various voltages and got the following:
Percentage of full light output at various voltages, with 12.6 volts
being "100%" :
12.6v = 100%
11.5v = 75%
10.3v = 50%
8.7v = 25%
At 10.3volts they only put out 1/2 of their full light output!
The highbeam current on a 65w bulb is about 5.15 amps, 2 bulbs makes 10.3amps Consider that if the *total* resistance of all the wire, connectors, headlight switch and dimmer switch is equal to only 0.3 ohms (which isn't very much!), than with 10.3 amps flowing thru the circuit you will loose 3.09 volts in the wire and switches.
So, with a battery voltage of 12.6, the bulbs only see 9.5 volts. That's over 1/2 of Your potential light output thrown away right up front! The voltage loss on my '71 wiring was about 3 volts before I did the relays, now it's about 0.4 volts.