High beams not working...

I would check the fuses first. Headlights are typically on a separate fuse then the parking lights. If the fuse is fine check and see if the Bulb is burnt out but it is rare for both lights to go out at the same time.

Do you know how to test electrical circuit's using a wiring diagram an a voltmeter ? Reading how the headlamps are suppose to work ,then testing is how to find the problem .
Headlamps
The headlamps may be turned ON 2 different ways. First, when the driver places the headlamp switch in the HEADLAMP position, for normal operation. Second, with the headlamp switch placed in the AUTO position, for automatic lamp control (ALC). During ALC, the headlamps will be OFF in daylight conditions, or low beam operation in low light conditions. Battery positive voltage is supplied to the low beam relay and the high beam relay in the underhood fuse block. When low beam headlamps are requested, the body control module (BCM) supplies ground to the coil side of the low beam relay. This activates the relay and the relay supplies voltage to the left hand low beam headlamp through the LH LOW BEAM fuse and to the right hand low beam headlamp through the RH LOW BEAM fuse. Ground for the left hand low beam headlamp is provided at G101. Ground for the right hand low beam headlamp is provided at G102. When high beam headlamps are requested, the BCM supplies ground to the coil side of the high beam relay. This activates the relay and the relay supplies voltage to the left hand high beam headlamp through the LH HIGH BEAM fuse and to the right hand high beam headlamp through the RH HIGH BEAM fuse. Ground for the left hand high beam headlamp is provided at G101. Ground for the right hand high beam headlamp is provided at G102.

Free wiring diagrams here http://www.bbbind.com/free-tsb Enter vehicle info. Year , make , model an engine . Under system click on lighting , then under subsystem click on headlamps . Click the search button ,then the blue link .

Video's on youtube on electrical testing

check low beam fuse when switched on if it has voltage registering across the fuse ,if there is voltage across the low beam RHS fuse then it is possibly a pinched wire from the headlight running back towards inside of the car

You can't turn them on manually with the switch . You have the switch set on auto ?
Headlamps
You can use the headlamps in two different ways.
• Place the headlamp switch in the ON position for normal operation.
• Place the headlamp switch in the OFF position for automatic lamp control (ALC). During ALC the high beam headlamps are On at reduced intensity for daytime running lamp (DRL) operation in daylight conditions, or low beam headlamps On in low light conditions.
The DRL/EXT LTS fuse and the EXT lamps fuse in the underhood junction block supply battery positive voltage at all times to both of low beam lamps and to the right high beam lamp. The low beam circuit continues to the high/low beam switch, then, depending on the position of the dimmer switch, connects to the normally-open headlamp relay switch contacts. Placing the headlamp switch in the HEAD position provides a ground path for the headlamp switch input of the Body Control Module (BCM). After receiving this input, the BCM energizes the headlamp relay. When the headlamp relay is energized, the low beam circuit is connected to ground G201. The high beam circuit is divided into a left and a right side circuit.
The DRL/EXT LTS fuse in the underhood ignition block supplies battery positive voltage to both the coil and to the normally-closed contact of the DRL relay switch circuit. During high beam operation, the left side current flow is through the closed contacts of the DRL relay, and to the left high beam lamp.
The EXT Lamps fuse in the top of the engine fuse block supplies battery positive voltage to the right high beam lamp. Both high beam circuits are then connected together, and continue to the dimmer switch. When the driver closes the high beam contacts of the dimmer switch, the circuit is grounded at G201.
Both the headlight switch and the BCM provide a ground, or control circuit, to the headlight relay coil circuit for manual or automatic headlamp operation. When you place the headlamp switch in the OFF position, and the ambient light sensor indicates low light conditions, the BCM energizes the headlamp relay for low beam operation. You may switch the headlights to high beam by pulling the dimmer switch handle toward you until the dimmer switch is activated. When the dimmer switch is placed in the HIGH position, the indicator lamp input to the BCM is pulled low. The BCM then sends a class 2 message to the instrument cluster in order to illuminate the high beam indicator lamp.
If the headlamp switch is left in the head position, the inadvertent power control feature will turn off the headlights 10 minutes after you turn the ignition switch to the OFF position. If you place the headlamp switch in the head position after the ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the headlights will remain ON until you turn them OFF or until the battery runs dead.

On a 2008 Prius, If both High beams work but only one side has working low beams, then it is most likely a fuse. So before breaking your knuckles to change the bulb, check the fuse first. I found out the hard way as my mom distressed to me that her drivers side headlights were out. So without checking to see if low and high were working, I proceeded to remove and replace the bulb - ouch! There are 4 10 amp fuses that protect the circuits for low/high beam function. They are under the hood in the fuse box on the drivers side and they are marked on the box cover. Check them before changing the bulb.

there are fuses for each light, high and lo beam. the grounds are grounded at all times, I dont know what you mean by open seeking. its wired like every other car. Right low beam is fuse 21 Red/White wire should be hot if fuse is good. I dont know what you mean by hooking low beam connector to battery? check fuses.

Check the fuse. There are seperate fuses for right and left. You dont mention if the high beam works for that side? If it does, the fuse is good. The GREEN wire at the bulb is the ground for the low beam. If that wire has power, then the ground is bad. If the high beam works, the hi'lo beam switch is good, and there is a problem between that headlight and the Engine Compartment Junction Block

At first 1994 C280 high beams began to not connect regularly when stick pushed forward, then not at all. Drove high beams by pulling and holding stick back towards steering wheel until that stopped working, too. Shop said the turn signal switch was at fault-- had seen it many times before with W202; about $160 to replace. Haven't done it yet, but should be an easy fix?

Low Beam Fuse may be bad.
Low Beam relay position is bad.
Stalk that controls the high/low beams/cruise/lights is bad.
Low beam filament may be bad in both headlamps.

headlight relay is under the screwed down portion of the fusebox.