Only high beam works. Why don't my low beams work or my car horn. Relay, dimmer switch and new lights replaced. Still only works on one beam. High beam sensor light stays on in the dash of the car all the time except when car is not running.

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.
Low and High Beams Headlamps Inoperative ?
Replace the headlamp switch. Refer to Headlamp Switch Replacement .
Did you check the headlamp relay ? Location ,left instrument panel
Did

Well there is a fuse and a low beam relay. The relay is grounded by the dimmer switch and the lights are grounded at the light socket in the wiring. The relay is also powered by the ignition switch.
Do you have power at the relay and the low beam circuit at the light? I'm assuming you have a good ground at the light if the high beam circuit works.

Headlamps Inoperative - Low Beams

Step

Action

Value(s)

Yes

No

DEFINITION: This diagnostic procedure should only be used if the high beam headlamps are operating properly and the low beams are inoperative.

1

Did you perform the Headlights System Check?
--
Go to Step 2
Go to Headlight System Check

2

1. Turn the headlamp and panel dimmer switch to the ON position.
2. Move the headlamp dimmer switch to the LOW position.
3. Backprobe the headlamp dimmer switch connector with a J 35616-200 from cavity A to ground.

Does the test lamp light?
--
Go to Step 3
Go to Step 5

3

1. Remove the daytime running lamp relay.
2. Connect a J 35616-200 at cavity G5 to ground.

Does the test lamp light?
--
Go to Step 4
Go to Step 6

4

1. Re-install the daytime running lamp relay.
2. Backprobe cavity B at the high/low beam headlamp with the headlamp dimmer switch in the LOW position.

Does the test lamp light?
--
Go to Step 7
Go to Step 8

5

Replace the headlamp dimmer switch.

Is the repair complete?
--
Go to Headlight System Check
--

6

Repair the open in CKT 359 (PPL) between the headlamp dimmer switch and the daytime running lamp relay.

Is the repair complete?
--
Go to Headlight System Check
--

7

Replace the high/low beam headlamps.

Is the repair complete?
--
Go to Headlight System Check
--

8

1. Inspect for an open in CKT 12 (TAN) between the daytime running lamp relay and S120, repair as necessary.
2. Replace the daytime running lamp relay if no open was found in CKT 12 (TAN) between the daytime running lamp relay and S120.

Is the repair complete?
--
Go to Headlight System Check
--

Replace any blown fuses, and check or replace the head light relay.

The headlight relay provides power to the dimmer relay, then power goes thru a fuse for each light for each circuit (4). The low beam fuses are in fuse block 2. The dimmer relay is controlled by the daytime running light module. The headlight and dimmer switches send signals to the DRL module. You may need a shop manual to troubleshoot the circuits.

Are you getting power in and out of the dimmer switch for both high and low circuits ?

The high and low beam lights use the same power source, so if the low beams work the high beams have power.
There is a low and high beam relay controlled by the dimmer switch.
If the low beams work and the high beams don't, and the bulbs are good, check the dimmer switch and the high beam relay.

I'm not sure exactly what your problem is. When you "click" your lights to low beam, your high beams should not work. But if your low beams work when you "click" them on, but your high beams don't work when you "click" them on, you either have a blown fuse, bad relay or high beam elements burned out on both lamps. (Not so unusual) Possibly a bad "dimmer" stalk switch or bad wiring, too, but a little less likely.

Good day:
the following is what you can do to test to see whats going on
turn on the headlights,put in high position
2.leave light in high, disconnect the head light dimmer switch, connect a fused jumper between head light relay supply voltage circuit of the dimmer switch and the control circuit of the head light relay. if the high beams come on then replace the dimmer switch, if the high beams don,t come on then.
3.use a fused jumper across the battery positive voltage supply circuit and the switched high beam voltage supply circuit. if the high beam come on now replace the head light relay, if the high beams don't come on then you will have to replace the LH I/P fuse block. I would most likely say that it's the relay just because of the year. I gave you a lot here I hope this helps

Cheers

it could be Bad dimmer switch .just check out the switch.