Headlamps work all the time

You very well could have a couple of faulty relays 45 & 46 in the underhood fuse / relay box . Could also have DTC'S - diagnostic trouble code's stored in the BCM - body control module .
DTC B2575 Headlamp Control Circuit
When the body control module (BCM) senses a request for headlamp or daytime running lamp (DRL) illumination, the BCM sends a pulse width modulated (PWM) ground signal to the low beam headlamp driver module through the low beam headlamp driver module control circuit. The low beam headlamp driver module will illuminate the headlamps, adjusting the intensity based on the PWM signal received.
DTC B2585 Park Lamp Control Circuit
When the body control module (BCM) receives a ground signal from the headlamp switch commanding to illuminate the park lamps, the BCM will energize the park lamp relay by grounding the park lamp relay control circuit.
DTC B3802 Park Lamps Request Circuit
The body control module (BCM) monitors the park lamp switch signal circuit and the headlamp switch headlamps on signal circuit in order to determine when the park lamps and headlamps should be illuminated. When the headlamp switch is turned to PARK, the BCM senses that the park lamp switch signal circuit is grounded and the headlamps switch headlamps on signal circuit is open. The BCM will then energize the park lamp relay illuminating the park lamps. When the headlamp switch is turned to HEAD, the BCM senses that the park lamp switch signal circuit and the headlamp switch headlamps on signal circuit are grounded. The BCM will then energize the park lamp relay and headlamp driver module (HDM) illuminating the park lamps and headlamps.
relay # 46 is the HDM headlamp driver module .

The headlamps are controlled by the BCM - body control module , do you know what that is ? The headlamp switch is a input to the BCM ,the BCM energizes relays to turn on the headlmps , low beam relay , high beam relay , DRL relay . These relay's are PCB - printed circuit board relay's ( non - serviceable ) If found to be bad the whole under hood fuse box would need to be replaced .
Low Beam Headlamp Operation
The low beam headlamps may be turned ON in 3 different ways:
• When the headlamp switch in the HEAD position for normal operations
• When the headlamp switch is in the AUTO position, for automatic lamp control (ALC)
• When the headlamp switch is placed in the AUTO position, with the windshield wipers ON in daylight conditions, after a 6 second delay
Battery voltage is applied at all times to the coil and switch sides of the LOW BEAM PCB Relay located in the underhood fuse block. When the headlamp switch is placed in the HEAD position, ground from G202 is applied through headlamps ON switch signal circuit to the body control module (BCM), signaling the headlamps ON request. In response to this signal, the BCM applies ground through the headlamp low beam relay control circuit energizing the low beam relay. With the relay energized, battery voltage is applied through the switch side of the relay, the left and right low beam fuses, and the low beam supply voltage circuits illuminating the low beam headlamps. Ground for the left headlamp is provided at G101 and the right headlamp at G100.

Do you know what B codes are ? BCM - DTC'S - diagnostic trouble codes , need a factory scanner or professional one to view these codes , not autozone or advance etc....Having a qualified repair shop check your vehicle would be your best bet.

DTC B2575 00: Headlamp Control Circuit

Circuit/System Description
The vehicle headlamps are controlled by the body control module (BCM) based on inputs from the headlamp switch and the turn signal/multifunction switch. The headlamp switch has four positions: Off, Auto, Park, and Headlamps. The default headlamp switch position is Auto, in which the BCM uses the ambient light sensor to determine when headlamps are needed. The Off portion of the headlamp switch is a momentary switch which overrides the automatic headlamps and will turn off the vehicle headlamps. When in the Off position, the headlamp switch grounds the headlamp switch headlamps off signal circuit, prompting the BCM to turn off the headlamps. The Park position of the headlamp switch will only illuminate the vehicle parking lamps. The Headlamp position of the headlamp switch will illuminate both the parking lamps, as well has the headlamps. With the headlamp switch in the Headlamp position, the headlamp switch headlamps on signal circuit is grounded, prompting the BCM to turn on the headlamps, regardless of other factors such as ambient light.
The headlamp high beams are controlled through the flash to pass switch and the headlamp dimmer switch, both located in the turn signal/multifunction switch. The flash to pass switch is a momentary type switch, designed to illuminate the high beams as long as the switch is held. With the switch closed, the flash to pass switch signal circuit is grounded, prompting the BCM to turn on the high beam lamps. The headlamp dimmer switch allows the operator to select between full time high or low beam operation. Unlike the flash to pass switch, it is not a momentary switch. When the headlamp dimmer switch is in the high beam position, the headlamp dimmer switch high beam signal circuit is grounded. This prompts the BCM to turn on the high beam lamps.
The BCM controls the headlamps based on the inputs explained above. When a low beam request is received, the BCM grounds the headlamp low beam relay control circuit. This energizes the coil in the LOW BEAM PCB relay, causing the relay switch to close. This then applies B+ to both low beam headlamps through the LT LO BEAM and RT LO BEAM fuses, illuminating the low beam headlamps. When a high beam request is received, the BCM grounds the headlamp high beam relay control circuit. This energizes the coil in the HIGH BEAM PCB relay, causing the relay switch to close. This then applies B+ to both high beam headlamps through the LT HI BEAM and RT HI BEAM fuses, illuminating the high beam headlamps

First , do the headlamps work ? There is a fuse for the headlamp switch F2.17 - 15 amp located in the central junction box ( inside the vehicle fuse box ) also F2.7 a 30amp . . When you turn on the headlamps or just park lamps the dash lights an the running light's should come on . I see in the wiring diagram that there is a microprocessor involved in the operation of the lights . Also i see there is a relay PARK LAMP relay located in the vehicle security module .

Do your headlamps work ?
Park/Marker/License/Tail Lamps
Voltage is applied to the turn/headlamp switch at all times. When the turn/headlamp switch is in the PARK or the HEAD position, voltage is applied to the following components:
?€¢
The park lamps

?€¢
The marker lamps

?€¢
The tail lamps

?€¢
The license lamp

The front marker lamps are grounded through the turn filament of the respective front park/turn lamp. The front marker lamps light as a result.
The automatic lamp control function turns on the park lamps and the headlamps. This action occurs when the ambient light sensor determines that the exterior lamps should be turned ON based on the amount of available light. When the BCM grounds the park lamp relay, voltage is supplied directly to the park lamps, bypassing the turn/headlamp switch assembly. When this action occurs, the following conditions exist:
?€¢
The automatic lamp control relay is grounded.

?€¢
The headlamps turn ON. Refer to Headlights/Daytime Running Lights (DRL) Circuit Description .

The lamps turn OFF when the BCM does not ground the park lamp relay or the automatic lamp control relay. This action is caused by the following conditions:
?€¢
The available light reaches a predetermined level.

?€¢
The ignition switch is turned to the OFF position

Daytime Running Lamps (DRL) NOTE: The smart junction box (SJB) must be configured when installing a new module. For additional information, refer to Section 418-01 .
The DRL system operates the low beam headlamps at a reduced intensity. The SJB supplies pulse width modulated (PWM) voltage to illuminate the low beam headlamps at a reduced intensity when the following conditions are met:

• The headlamp switch is not in the HEADLAMPS ON position.
• The ignition switch is in the RUN position.
• The transmission is not in PARK (P).

This dealer only repair ,unless you have the ford IDS (factory scan tool ) .

You have a gremlin ! No , just kidding . No it's not the ignition switch ! The headlamps right an left have there own fuse in the under hood fuse box . LH HDLP - RH HDLP . Power direct to the head lamps an they ground through the headlamp switch when placed in high or low beams . Next time they come on wiggle the headlamp switch an see if they go out ! Does your vehicle have auto lights ? Day time running lamps ? The BCM - body control module controls Automatic lamp control !
Battery voltage is applied to the headlamp bulbs at all times. The headlamps are controlled by supplying the ground for the lamps through the turn/headlamp switch assembly or the body control module (BCM). When the turn/headlamp switch is in the ON position, the ground is supplied through CKT 150.
The BCM controls the daytime running lamps (DRL). The system allows the headlamps to operate at a reduced intensity under the following conditions:
?€¢
The engine is running.

?€¢
The transaxle is not in the PARK position.

?€¢
The normal headlamps are turned OFF.

The BCM activates the system by grounding CKT 592. This action energizes the DRL relay. This condition allows a reduced voltage to flow to the headlamps. When the headlamp switch is turned to ON, the headlamps operate normally.
The parking brake provides an input to the BCM. When the parking brake is engaged, the DRL remain disabled until the parking brake is disengaged.

Your vehicle is equipped with an "Auto Lamp" system. The headlamps will stay on for as long as 3 minutes depending on how you have the control set. If you are certain that this is not the problem and/or your headlamps will not turn off after 3 minutes, perform these checks:

1. CHECK HEADLAMP SWITCH OPERATION
Ensure that the headlamp switch is off. Disconnect the headlamp switch connectors. If the headlamps go foff, replace the headlamp switch. If the headlamps are still on, go to the next step.

2. CHECK CIRCUIT No. 15
Remove autolamp parking lamp relay from the under hood Power Distribution Center (PDC), near the battery. If the headlamps are off, go to the next step. If the headlamps are still on, repair the short to battery voltage in circuit No. 15 (RED/YELLOW wire).

3. CHECK AUTOLAMP RELAY GROUND CIRCUIT
Remove the autolamp parking light relay from the PDC. Measure the resistance between ground (BATTERY NEGATIVE) and terminal No. 2 (DARK BLUE/ORANGE wire) at the autolamp relay wiring harness connector. If resistance is 5 Ohms or less, continue to the next step. If the resistance is more than 5 Ohms, replace the autolamp relay.

4. CHECK THE LIGHT SENSOR AMPLIFIER
Reconnect all components. Disconnect the light sensor amplifier located in the defroster grille on the top of the dash. If the headlamps are off, replace the light sensor amplifier. If the headlamps are on, repair short to ground in circuit No. 218 (WHITE/PURPLE wire) to the headlamp switch.

SECTION 417-01: Exterior Lighting 1999 Explorer/Mountaineer Workshop Manual REMOVAL AND INSTALLATION Procedure revision date: 07/27/1998 Lamp Assembly-Headlamp (Explorer) Removal

1. NOTE: Make sure that the headlamp switch and the ignition switch are in the OFF position.
   Remove the parking lamp assembly. Refer to Lamp Assembly-Parking (Explorer) or Lamp Assembly-Parking (Mountaineer).

1. Remove the headlamp assembly.
   1. Compress the self-locking tabs.
   1. Remove the headlamp assembly.
   1. Disconnect the electrical connector.

Installation

1. To install, reverse the removal procedure.
   • If necessary, adjust the headlamps. For additional information, refer to Headlamp Adjustment-Photometric Aiming or Headlamp Adjustment-Screen Method Aiming in this section.

I have a 1997 cadillac deville that has both 'daytime running lamps' when put into gear and 'twilight sentinel' which turns the headlamps and parking lamps on at night, and goes off during the day or when it is bright enough.

There is an adjustable delay for the twilight sentinel to turn the headlights off after the ignition key is removed and it is night time.
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I had the 'daytime running lamps' installed on a 1990 Cadillac Deville that turns the headlamps only on when the ignition key is switched to on with an aftermarket module. The headlamps are about 70% or so as bright as the regular twiilight sentinel headlamps and parking lights and are designed to go on during the day.

The twilight sentinel overrides this feature when it gets dark outside.

I had the daytime running lamps installed by an auto electric shop that specializes in electrical systems, alarms, stereos, etc.

Does this help?

What relay's ?
The instrument cluster controls the headlamp systems that include daytime running lamps (DRL). The system allows the headlamps to operate at a reduced intensity when all of the following conditions apply:
• The engine is running.
• The transaxle is not in the PARK position.
• The normal headlamps are not on.
The instrument cluster turns the DRL system on by grounding CKT 592, thereby energizing the DRL relay. This action allows a reduced voltage of 6 volts to flow across the headlamps. If the vehicle has the optional fog lamps, the fog lamp relay will also be energized. The park lamps will turn on and the fog lamps will operate normally. When the headlamp switch is turned to the ON position, the instrument cluster allows normal headlamp operation.
The instrument cluster also has an input from the park brake. If the park brake is in the ON position, the DRL will remain disabled until the park brake is placed in the OFF position. On vehicles with an automatic transaxle, the instrument cluster will disable the DRL until the transaxle has been taken out of the PARK position.

Headlamps Inoperative - High Beams
Step
Action
Value(s)
Yes
No
1
Did you perform the Daytime Running Lamps (DRL) System Check?
--
YES - Go to Step 2
NO - Go to Daytime Running Lights (DRL) System Check
2
Disconnect the turn/hazard headlamp switch connector C1.
Connect the fused jumper between terminal B of the turn/hazard headlamp switch assembly harness connector C1 and ground.
Do the high beam headlamps operate?
--
YES - Go to Step 3
NO - Go to Step 4
3
Replace the turn/hazard headlamp switch assembly.
YES - Did you complete the repair?
--
NO - Go to Daytime Running Lights (DRL) System Check
--
4
Repair the open in CKT 1200 between the turn/hazard headlamp switch assembly. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?
--
Go to Daytime Running Lights (DRL) System Check
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