Single Relay Headlight Wiring Upgrade for Early Jeep Wagoneers

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.

So what's the difference between the single relay and dual relay setups then?
Well, this set of instructions (single relay) keeps the lighting pretty close to stock, 2 headlights with each bulb having a high and low beam - thats it. 30 years ago when these wagons were made headlights didn't suck a lot of juice, and they didn't put out a lot of light either. Yea, I know. Rocks were a lot heavier back then also. But the headlight switch won't handle the current requirements of the newer bulbs, especially the older stock switches, and the switches tend to heat up resulting in all kinds of nasty scenarios. Use these instructions if you want to install upgraded headlights and are not going to enhance your lighting much beyond that.

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.

How do I find the dual relay instructions?
Click here to read the dual relay setup instructions, it also has info on how to wire the parking lights/blinker circuits.

Single Relay Setup Table of Contents

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

The Usual Disclaimer

Level of Difficulty

Time Required


List of Tools and Parts

  1. wire crimper, ~$15 (a crimper for un-insulated lugs is a bit more expensive but better, remember - do it once, do it right)
  2. wire snips
  3. multi-meter with Rx1 scale and something very close to a 12v DC scale (RadioShack Meter Cat.#: 22-218, $10)
  4. thin blade straight slot screwdriver
  5. larger phillips screwdriver
  6. standard phillips screwdriver
  7. standard straight slot screwdriver
  8. electric drill with bit sized for the sheet metal screws listed below
  1. 1 pack spade lugs, (I prefer un-insulated lugs, they fasten with 2 crimps vs one crimp on the insulated lugs)
  2. 1 large round eye lug that will fit over the battery crimp bolt
  3. 1 small round eye lug for the relay ground lug
  4. 1 sheet metal screw for the ground
  5. 4 straight crimp connectors
  6. 20 ft or so of #10 gauge wire for headlight circuit
  7. 6 inches, fused wire, 30 amp
  8. 2 ft, shrink wrap tubing to cover exposed crimps
  9. 1 sheet of 400 grit sandpaper
  10. 1 pack tie wraps, small to medium sized, keeps wire attached (~$5-8 for a large pack)
  11. 1 pack small spiral wrap, keeps wire attached, ~$3
  12. 2 30 amp fuses (1 spare)
  13. 2 10 amp fuses (1 spare)
  14. 1 30 amp fuse box with at least 2 outputs, but 4 outputs would be better>
  15. 1 Bosch 0-332-019-150 30 amp relay, napa pn# ar230, ~$7 -- or radio shack pn 900-2394
  16. 1 3/4" sheet metal screw for mounting the relay (size the screw according to the size of the mounting hole in the relay, the relay does not come with screws, the fuse box might - be sure to check before leaving the store. I think i used a #12 screw for the relay)
  17. 1 12 gauge wire nut
  18. 1 floor mounted dimmer switch, napa pn# ACDD808 (ac delco, ~$9) or ECHDS115 (echlin, ~$9)
  19. 2 Sylvania H6024XV headlights, Pep Boys, ~$25 for both bulbs/ $12.50 each or autobarn (see addendum for sylvania contact info)

Notes, etc

START HERE - Disconnect the battery

Step 1: Removing the headlights

Step 2: Checking your existing headlight circuits

Step 3: Cleaning your connectors

Step 4: Install the new bulbs

Step 5: Install the new dimmer switch

Step 6: Install the new fuse box

Step 7: Install the new relay

Step 8: Wiring the wag

Step 9: lets review

Step 10: Action, Camera, Lights!

Step 11: Troubleshooting

Images and Pictures

Figure 1 - Bosch 0-332-019-150 30 Amp Relay

pin connections image
Figure 2 - Headlight and blinker wiring block connector. Lug with green wire is hi beam power, brown wire is lo beam power, leftmost lug is parking light power.

Figure 3 - Headlight connector drawing

Figure 4 - Drawing of headlight switch w/circuit designations

Figure 5 - Dimmer switch drawing

click for full sized image
Figure 7 - Simple wiring schematic for headlights and parking lights, click for full sized image



Power Drop Information

taken off the net from a ford truck group list...

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.

Sylvania Contact Info

Sylvania Website, info on H6024XV headlights
Sylvania National Customer Service Center: U.S.A., Automotive Lighting: 1-800-347-3420
Sylvania National Customer Service Center: Canada, Automotive: 1-800-265-2852

Wire size requirements for amperage vs. length of run

in Wire
at 12V
#14 #12 #10 #8 #6 #4 #2 1/0 2/0 3/0
1 12 84 131 206 337 532          
2 24 42 66 103 168 266 432 675      
4 48 18 33 52 84 133 216 337 543 675  
6 72 14 22 33 56 89 141 225 360 450 570
8 96 10 16 27 42 66 108 168 272 338 427
10 120 8.5 13 22 33 53 84 135 218 270 342
15 180 6 8.5 13 22 35 56 90 144 180 228
20 240   6.6 10 16 27 42 67 108 135 171
25 300     8 13 22 33 54 86 108 137
30 360     6.6 11 18 28 45 72 90 114
40 480       8 13 21 33 54 67 85