1986 300zx - Right headlight does not work on low beams, but does on high beams.

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.

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?
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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
--

If the lgihts go out when low beam is selected, both low beam lamps may burned out! It is possible that you drove the vehcile with one low beam not working and didn't notice. The second failed and now you noticed!

If not, there is a headlight relay that selects high/low beam current to the headlights, but those things seldom fail. Check your owner's manual to find its location and replace it.

no year, is it a 1973 Civic?
water there is 100% normal, huge water forces there... at 85mph.?
why not post the symptoms so we can help?
are both lamps dead, left and right????????????
yes, fuses. all fuse in both boxes, they are marked head lights.
most cars , not all have 2 fuse. one for each lamp. so both dont die
together, (big danger that)

if one lamp is dead, use a voltmeter, at the lamp
got 12vdc there, HL switch on, then the lamp is burned out.
measure at the socket, connected.

Check for loose contacts in the light socket. Also, most vehicles use separate relays for passenger and driver side headlights, so be sure to check those.

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.

you need new headlight

Hi Every single time I have had a failure of low beam in a headlight without failure of high beam, it has been because the lamp bulb or halogen lamp module has reached the end of its serviceable life, not because of any wiring problems. Low beam burns out first because it is on the most. If low beam is lost simultaneously in both headlights, I would check fuse first, then the headlight switch. If low beam is lost on one side only, it is almost always going to be due to the bulb or lamp module needing to be replaced. In that case, replace them in both headlights because the other one will be going kaput in short order, as well.Also if you already replaced the fuse and bulb check the headlight dimmer control switch.
Thanks for using Fixya.

Hi,
It has been because the lamp bulb or halogen lamp module has reached the end of its serviceable life, not because of any wiring problems. Low beam burns out first because it is on the most. If low beam is lost simultaneously in both headlights, I would check fuse first, then the headlight switch. If low beam is lost on one side only, it is almost always going to be due to the bulb or lamp module needing to be replaced. In that case, replace them in both headlights because the other one will be going kaput in short order, as well.
Most like the low beam filiment is bad but the high beam filiment is still good, try replacing bulb. If replacing bulb does not fix problem then you probably have voltage problems and should check the voltage reading and the plug.
OR
isolate the wire that comes from the headlight switch to the headlamp bulbs for low beam and check to see if there is a short in the wire. You can find this wire by using a test light turn on the key and get a good ground with the test light poke the wire and see if the test light illunimates with the headlight switch on.
check the wires, and check the fuse for your lowbeams. could of blown a fuse on your lows, but your highs will still work.

The fuse box is located in the engine compartment,on the driver's side. Has thumb-screw retained cover.
Thanks for contacting fixya.com

You headlight lamp have a diffuser mechanism which allows it to flip between the hight beam and low beam feature of the bulb. In fact, you high beam will function even if the low beam is not working.

I would recommend the purchase of the new headlight lamp. It would cost you you any where from $15.00 per unit to get a replacement lamp