High beams work, low beams do not. What is wrong with headlight?

Question

I have a 2000 Jeep Wrangler TJ and the high beams work but the low beams don't.

I replaced one of the relays under the hood and the high beams started working but the low beams still don't work. What else could be the problem?

Answer 1

There are a few things that could be problems:

1. Confirm that the bulbs are good. I've seen it happen more than once that one bulb burns out and you don't notice, then the second bulb burns out and that is when you notice.
2. Check the fuses. On many cars the high and low beams are fused separately.
3. Check, or listen, to determine if the relay controlling the lights is operating when you switch from low to high (if it is you can be pretty sure that the control circuits are working).

Answer 2

Perform a continuity test on your combination switch. Get a multimeter and service manual for your vehicle and test the contacts with the switch in different positions.

Answer 3

2003 owner and non-mechanic. Had an issue where high beams worked but only the passenger side low beam would work. How to diagnose and fix?

1. Take out both headlights and swap to see if you get the same result. When testing you don't need to re-install them just plug them in. Taking them out is easy to do and you can have them both out in under 10 minutes - all you need is an alien wrench set. They're super cheap so buy one if you don't have any. Using that wrench remove the 3 screws from the metal headlight retainer. They are very visible and easy to remove. Once removed there are 4 more similar screws holding the headlight to the bracket. Once all screws are out Wiggle the plug off. Swap and test. If you get the same result it's not the light.

So what next? Well, if it's not the light itself its got to be the wiring or a fuse or relay.

2. Open the fuse box which is located under the hood. The fuse box is located next to the batter and is very easy to open - just push the two side closest the battery together and it lifts right up. There's a diagram that shows you what each fuse is. It's probably a 40 green fuse. You should probably use a fuse puller but you can just as easily get it out with pliers. When pulling don't squeeze hard just lightly and wiggle. If you squeeze to hard you could potentially crush the fuse. If visually it looks good put it back in and seat it tightly. Check lights to see if anything changed.

Still not working? Probably a wiring problem.

3. Think of the wiring this way; everything electrical for the most part goes to/thru the fuse box before continuing its journey. For the lights the wiring goes from the fuse box to the passenger side light and then that wire extends from that plug via wire to the driver side light. They're basically daisy chained. The passenger side will have one black, 2 thick red and 2 thick purplish wires (colors may vary). The driver side only has one each because those wires connect to the same plug that connects to the passenger light. Again think daisy chaining wires. If you pulled the plug from the passenger bulb the right would go out too. This is probably where your problem is. After many years the wiring and connectors become brittle and crack easy. Some melt depending on where they are and some are just badly weathered. Examine that plug on the passenger side closely. Make sure the wires are secured to the connector/plug and the connector/plug is not melted/distorted.

The problem with my jeep is that one of the wires on the connector/plug that connects to the passenger side headlight was completely rotted off. I replaced the connector, which is something you may or may not want to do, and BAM both low beams and highs work again.

Painless Wiring 80300 H4 Headlight Plugs for 76-06 Jeep CJ Series, Wrangler YJ & TJ & Cherokee XJ. Found mine on Quadratec website.

Good Luck