My headlights do not work on brights. - 2000 Ford Ranger SuperCab

There could be several potential causes for both the tail lights and headlights not working and for the headlights turning on the brights when the vehicle is placed in gear. Some possible causes include:

1. A blown fuse: If a fuse has blown, it can cause the lights to stop working. Check the fuse box and replace any blown fuses.
2. A problem with the wiring: If the wiring has become damaged or has come loose, it could cause issues with the lights.
3. A malfunctioning light switch: The light switch might not be functioning properly, which could cause the lights to not work.
4. A problem with the headlight switch: If the headlight switch is malfunctioning, it could cause the headlights to turn on the brights when the vehicle is placed in gear.
5. A problem with the dimmer switch: If the dimmer switch is not functioning properly, it could cause the headlights to turn on the brights when the vehicle is placed in gear.

It's recommended to have a mechanic diagnose the issue to determine the cause and recommend the necessary repairs.

You have a bad ground wire in the headlight wire harness

Check your head light bulbs, your truck has the dual filiment headlight bulbs one per side which does both high beam and low beam, 9007 bulbs.
If the low beam filiments are burned out only the high beam will work.
Also look into finding out if the headlight switch is gone bad.
The headlight module and or drl module maybe defective.

check the headlight relay possibly under the hood

Most headlights have two different bulbs: one for regular/dim and one for bright. It's time to replace your headlights.

This is a common problem and is caused by a burnt headlight switch and headlight switch connector, replace both of them,

i had this happen with my dodge ram 1500. the guy i bought it from put 350 dollar moon lit lights in with leds and they looked impressive but the issue was that they didnt go bright and i could only see 40 feet in front of me and i was sure taping led flashlights would have done me more good that those stupid headlights. then i had the idea of if the brights work and the dims dont then that means no electricity is getting to the dims so i decided to bridge the power from the bright headlight to the dims and it made all four work. now they all work, and only on bright. so im figuring there is a issue with the wiring in the truck. so this is a temporary solution if you really need just plain old lights like i did because i live out in the country

might have to replace the headlights/bulbs. I have an 85 rx7 and I didnt have low beams only high and I replaced both headlights and now they work.

I had the same problem. The solution is simple; the ignition switch needs to be replaced. This is an easy do-it-yourself project. Here are instructions:
http://forums.vwvortex.com/zerothread?id=2532481
Check for a switch on ebay, they are about $15. After 10 years they wear out.