Last night I was driving down a dark country road and all of a sudden my headlights went out after hitting a small bump. No panicing, sort of, I turned on my hazard lights and from their light, found the edge of the road and stopped safely. After working the dash switch, I got nothing. Then I tried the high/low beam switch. The blue indicator worked, but still no lights! Working with a flashlight in my hand, I checked the headlight switch 30amp fuse, which was good. I was thinking it was very unusual to loose both the high and low beams at the same time, then it hit me! I have the upgrade headlight harness installed which has it's own fuse! D'oh! After finding the fuse holder in the harness and opening it, I just touched the fuse and the lights came on! Okay, I pulled the fuse and cleaned it's contacts, putting it back in. Problem solved.

This whole thing was a learning experience and a shocking one at that! This is also a warning to those of you who also have that type of harness installed. Drive safe!

 

Betcha that scared the crap out of you at first. I know my old GranTorino had a bad headlight switch and that happened 3 times before I decided better go ahead and replace it and it did me all 3 times ...lol. Also whats the upgrade headlight harness?

 

"Consider these facts on voltage drop. A Halogen headlamp is rated to produce 100 % of its rated light output at 13.5V. When voltage at the headlamp drops by 5 % to 12.82V the light output drops to 83 % of normal. When voltage drops by 10 % to 12.15V the light output drops to just 67 % of what it ought to be. A mere 1.35V of lost voltage has robbed you of 33 % of your light output. And it gets worse as voltage is further reduced."

Out here in the damp and wet Northwest If the ground connections connections are disconnected and wire brushed back to shiny metal as when new, original headlight brightness is restored and we don't need an upgraded headlight harness unless we're pushing high wattage lights. YMMV depending on conditions in your location.

 

On the XJ's & a lot of other cars, the power to the headlights runs through the headlight switch in the dash. The "upgrade headlight harness" uses relays to trigger the headlights. Right now, if you take a Ohm meter to the headlights, you will see there is not 12 volts going to the headlights. By upgrading the headlight harness, you will be closer to 12 volts and you will see brighter headlights.

www.danielsternlighting.com/home.html
www.cruiser54.com/?s=Headlight
www.putco.com/heavy-duty-wire-harness-relay

 

With ANY electrical circuit regardless of voltage, any time a switch either makes or breaks contact, an arc is formed. The arc you see is vaporized metal and after a while will pit the contact surface increasing resistance. Resistance causes heat and this heat can melt parts of the switch and not cause the fuse to blow. Resistance does however reduce the voltage going thru it. Case in point, I was running a rooftop flasher with a 55w halogen bulb in it using a cigarette lighter plug which is only held in contact by spring pressure in the socket. I had it fused at 5amps and it was melting the plug yet not blowing the fuse. I changed the power plug to a 1/4" audio plug and jack and fixed the problem.

The XJ headlight circuit sends all the power to the headlight switch, then thru the steering column dimmer switch, then to the headlights. I believe each halogen headlight draws about 4amps, but the relays only pull less than 1amp each. therefore the original switches should last quite a long time.

 

the PO put that in, dave?

 

And add arc suppression diodes to the relays and the whole works will outlive the owner !!

 

Or use the relays that have them built-in. Just pay attention to the polarity of the coil, so you don't nuke them though.

 

Taking the load off the switch is, all by itself, good enough reason to add a headlight relay.

 

Shining up the connection still doesn't fix the undersized wiring. Pushing 10-amps through around 10-feet of 16-gauge wire will drop 0.8 volts. That's ignoring the losses upstream of the headlight switch, and the ground path. So, that 6% loss puts you around 80% of the power to the headlight that you could be getting by using a dedicated wiring harness of a reasonable size.

 

Tape or silicone those suckers..

 

No, I added that myself, thanks to Cruiser 54. My headlights were like kerosene lanterns before and now when I'm loaded, I get flashed when I'm on low beams! I used the Putco harness, BTW. The hardest part of the install was cleaning up the passenger's side headlight plug as the connection point. It was green! It really needed to be replaced, but I needed the jeep that night. Now I need to track down what's wrong with my factory fog lights. The switch illuminates and the main fuse is good, but I don't hear the relay clicking. It's not that important right now either.

 

Use dielectric grease. Get a tube and use it on all electrical connections and most of the "bad connection problems", will go away.

 

Yeah, with that bad connector, I went one step farther and covered it with liquid electrical tape after using an old point file to scrape it clean.

 

I agree with this, and run one fused relay for each Lo beam, (just one for both high beams), with dedicated + from battery and earths (on older vehicles)
saves headlight switch, ignition switch on some vehicles

My XJ has bright headlights, no special globes