I have a 2001 Ford Ranger XLT when I turn signal on it flashes in the circle light in head lamp not in signal/marker light on the side of headlamp

With a 12v test light test the connectors that the bulbs plug into to make sure there is current to that point. If so make sure that the ground is good.

To the dealer or some other qualified repair shop. Light's are controlled by SJB - smart junction box , ford's body control module .
Principles of Operation
The smart junction box (SJB) monitors the headlamp switch position by sending voltage reference signals on multiple circuits to the headlamp switch. At any given time, one of the signal circuits is routed to ground. If the SJB does not detect any of the inputs to the headlamp switch is active (routed to ground) for 5 seconds, the SJB turns on the exterior lights and keeps them on for 10 minutes after the ignition switch is turned off (or 10 minutes from the time the SJB does not detect any headlamp switch input if the ignition switch was already off). If the SJB detects multiple circuits short to ground, the SJB implements a planned strategy depending on the multiple inputs received. If either of these situations occur, the SJB should NOT be ruled immediately as being at fault. This is normal behavior of the SJB design as it has detected a fault with the inputs from the headlamp switch.
When the SJB receives an input from the headlamp switch indicating a request for the parking lamps, the SJB energizes the parking lamp relay (internal to the SJB), which supplies voltage to the exterior lamps.

• One or more parking, rear or license plate lamps is inoperative

• Fuse
• Wiring, terminals or connectors
• Bulb holder
• Rear lamp assembly (vehicles without pickup bed)
• Cab marker lamp
• Trailer tow exterior mirror (if equipped)
• SJB

• Go To Pinpoint Test O .

Pinpoint Test O: One Or More Parking, Rear or License Plate Lamps Is Inoperative
Refer to Wiring Diagrams Cell 92 , Parking, Rear and License Lamps for schematic and connector information.
Normal Operation When the headlamp switch is placed in the PARKING LAMPS ON position, the smart junction box (SJB) provides a ground for the parking lamp relay coil (integrated into the SJB). When the parking lamp relay is energized, voltage is routed through circuit CLS30 (VT/WH) to the front, rear, license plate, dual rear wheel marker, trailer tow exterior mirrors (if equipped) and cab marker lamps (if equipped). Ground is provided to the rear and license plate lamps through circuit GD176 (BK/WH). Ground is provided to the LH and RH front parking and side marker lamps through circuits GD122 (BK) and GD124 (BK/VT), respectively. Ground is provided to the trailer tow mirrors through circuit GD179 (BK/VT). Ground is provided to the cab marker lamps through circuit GD115 (BK/GY).

This pinpoint test is intended to diagnose the following:
• Fuse
• Wiring, terminals or connectors
• Bulb holder
• Rear lamp assembly (vehicles without pickup bed)
• Cab marker lamp
• Trailer tow exterior mirror (if equipped)
• SJB
• PINPOINT TEST O: ONE OR MORE PARKING, REAR OR LICENSE PLATE LAMPS IS INOPERATIVE CAUTION: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
  Test Step Result / Action to Take O1 DETERMINE IF ALL THE PARKING LAMPS ARE INOPERATIVE
  • Key in OFF position.
  • Place the headlamp switch in the PARKING LAMPS ON position.
  • Are all the parking lamps inoperative?
  Yes
  VERIFY the SJB fuse 22 (15A) is OK.
  
  If the vehicle is equipped with cab marker lamps, GO to O8 .
  
  If the vehicle is not equipped with cab marker lamps, VERIFY the SJB fuse 22 (15A) is OK. If OK, GO to O2 .
  
  No
  If the cab marker lamps are illuminated and all the remaining parking lamps are inoperative, GO to O2 .
  
  If all the cab marker lamps are inoperative, GO to O3 .
  
  If both trailer tow mirrors are inoperative, GO to O5 .
  
  For all others, GO to O6 .

Park, Tail, Marker, and License Lamps
The PARK/LAMP fuse in the instrument panel (I/P) fuse block supplies battery positive voltage to both the coil and switch sides of the PRK LAMP relay, also located in the I/P fuse block. When the headlamp switch is placed in either the PARK or HEAD position, ground is supplied to the BCM on the park lamp switch ON signal circuit. The BCM then applies a ground to the park lamp relay control circuit. This energizes the relay, applying voltage to all park, tail, marker, and license lamps. The park, tail, marker, and license lamps are also turned ON when the headlamps are commanded ON by the BCM for low light operation.
Ground for the headlamp switch is from G200. Grounds for the various lamps are as follows:
• G100 supplies the right front lamps
• G101 supplies the left front lamps
• G400 supplies the right rear lamps
• G401 supplies the left rear lamps

The park, tail, license, and marker lamps are turned ON when the headlamp switch is placed in either the HEAD or PARK lamp positions, or anytime the automatic light control (ALC) turns the headlamps ON. When the headlamp switch is placed in the park lamp or headlamp positions, ground from G304 is applied through the signal circuit to the BCM indicating the park lamp request. In response to this signal, the BCM applies ground through the park lamp relay control circuit energizing the PARK LP PCB Relay. With the relay energized, battery voltage is applied through the switch side of the relay, both park lamp fuses, and the supply voltage circuits illuminating the park, tail, marker, and license lamps. Free wiring diagrams here http://www.bbbind.com/free_tsb.html Enter vehicle info. year, make , model ,engine ! Under system click on lighting ,then under subsystem click parking lamps ! Click the search button then the blue link !

Go to http://www.bbbind.com/free_tsb.html free wiring diagrams ! You having tail light problems ? Do you know how they work ?

They are turned on by the BCM !
Park, Tail, Marker and License Lamps
The park, tail, license, and marker lamps are turned ON when the headlamp switch is placed in either the HEAD or PARK lamp positions, or anytime the automatic light control (ALC) turns the headlamps ON. When the headlamp switch is placed in the park lamp or headlamp positions, ground from G202 is applied through the signal circuit to the BCM indicating the park lamp request. In response to this signal, the BCM applies ground through the park lamp relay control circuit energizing the PARK LP PCB Relay. With the relay energized, battery voltage is applied through the switch side of the relay, both park lamp fuses, and the supply voltage circuits illuminating the park, tail marker, and license lamps. Ground for the left front park and marker lamps is provided at G101 and the right front park and marker lamps at G100. Ground for all rear lamps is provided at G302.
Turn Signal Lamps
The LT T/SIG and RT T/SIG fuses located in the underhood fuse block supplies battery positive voltage to the body control module (BCM) for turn signal and hazard lamp operation. When the turn signal switch is place in either the LEFT or RIGHT position, ground from G202 is applied through the turn signal switch signal circuit to the BCM indicating the turn signal request. In response to this signal, the BCM applies a pulsating voltage to the front and rear turn signal lamps supply voltage circuits cycling the lamps ON and OFF. The BCM also sends a message via GMLAN to the instrument panel cluster (IPC) to cycle the turn signal indicator ON and OFF depending on the position of the turn signal switch.
Ground for the turn signal lamps is supplied as follows:
?€¢
G101 provides ground for the left front turn signal lamp

?€¢
G100 provides ground for the right front turn signal lamp

?€¢
G302 provides ground for the left and right rear turn signal lamps

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

Without testing i would say you have DRL control module problem , But that would just be a guess .
In the night mode, the DRL ambient light sensor senses darkness. Then, the DRL module turns off the front turn lamps and turns on the headlamps through circuit 10. The DRL module also turns on the park, side marker, license, and tail lamps. If the engine should stall with the DRL control module in the night mode, the DRL control module will turn off the headlamps and leave the side marker, park, license and tail lamps on while the engine is being cranked. The headlamp switch operates as usual.
The Daytime Running Lamps (DRL) control module is designed to automatically operate exterior lights depending on outside light conditions. The DRL control module operates in two modes, the day mode and the night mode. In the day mode, the DRL ambient light sensor senses daylight. Then, the DRL control module turns on the front turn lamps (non-flashing) if under the following conditions:
• The ignition switch is on.
• The headlamps switch is in the OFF position.
• The park brake is released.

The brightness of the Vacuum Fluorescent (VF) displays is controlled by two signals: the park lamps on signal (circuit 230) and the VF dimming signal (circuit 308). With the park lamps on, the VF display of the radio, heater, A/C control (with RPO CJ2) and the instrument cluster will dim for nighttime viewing. When the park lamps on signal is not present (park lamps off), the VF displays are at high brightness for daytime viewing. When the park lamps are on, the I/P lamp dimmer switch provides a signal (VF Dimming Signal circuit 308) which controls the brightness of the VF displays when the I/P lamp dimmer switch is adjusted.

Do the Daytime running light's work ?

I have the same problem few days ago, and still didn't find any solution. Can any one please help?????18

It will turn on when I hit the button and the turn signals do work. All of this has led to my ABS lights to come on as well. ??????????? Your best bet , take it to a qualified repair shop or learn to do better explanation's ! Or lean to do automotive electrical testing .
Basic Electricity for Service Techs Ohm law Current Flow Opens Shorts
Electric Testing Techniques You Need to Know

How to Use Multimeter to Troubleshoot Common Problems

Do you know what a wiring diagram is ? How to use a DVOM - digital volt ohm meter ? Free wiring diagrams here http://www.bbbind.com/free_tsb.html Enter vehicle info. year make ,model and engine size. Under system click on lighting ,then under subsystem click on turn signals . Click the search button then the blue links .Check power an ground circuits ! This is how we diagnose electrical faults , not just replacing parts .

Turn Lamps
Voltage is applied through the TURN fuse and the turn/hazard flasher when the ignition switch is in the following positions:
• RUN
• BULB TEST
• START
The voltage travels to the contact in the hazard switch. The hazard switch is located in the turn/hazard-headlamp switch assembly. This contact is normally closed.
When the left turn signal is turned on, voltage is applied to the following components.
• The left turn indicator
• The left front park/turn lamp circuit 14
• The left rear turn lamp circuit 18
The turn lamps turn on immediately. The current flow heats up the timing element. The timing element is located in the turn/hazard flasher. The timing element repeatedly opens and closes the circuit. This action causes the turn lamps to begin flashing.
The voltage that is applied to the left front park/turn lamp is also applied to the left front marker lamp. If the headlamp switch is in the OFF position, the left front marker lamp will find a path to ground through one of the following lamps. The following lamps provide low resistance paths to ground:
• The right front marker lamp
• The right turn indicator
• The right front park/turn lamps
• The left front park/turn lamps
The left front marker lamp flashes with the turn lamps. The voltage drop across the marker lamp is much higher than the voltage drop across the other lamps. The lamps that are used for the ground path will not flash.
When the headlamp switch is in either the PARK or HEAD positions, voltage is applied through the following components:
• The EXT LP fuse
• The marker lamps
• The park lamps
When the left turn signal is turned on, the left marker lamp will have voltage at both connections. The left marker lamp does not light. When the turn/hazard flasher stops the voltage to the turn lamps, the marker lamp is grounded through the turn lamp. The marker lamp does not go on. The left front marker lamp flashes in the following manner:
• The left front marker lamp flashes on when the turn filament of the left front park/turn lamp goes off.
• The left front marker lamp flashes off when the turn filament of the left front park/turn lamp goes on.
Voltage is applied to the right lamps in the same manner, when the right turn signal is turned on.
Hazard Lamps
Voltage is applied at all times through the following components to the normally open contact of the hazard switch in the turn/hazard-headlamp switch assembly:
• The STOP HAZ fuse
• The turn/hazard flasher
When the hazard switch is turned on, voltage is applied to the following components:
• The front turn lamps
• The rear turn lamps
The following lamps flash on and off:
• All of the turn lamps
• Both of the turn indicators
The front marker lamps flash with the hazard lamps on, just as the front marker lamps flash when the turn lamps are on. If the headlamp switch is in the OFF position, the front marker lamps flash on when the hazard lamps are on. The front marker lights will flash on when the hazard lamps are on if the headlamp switch is in one of the following positions:
• PARK
• HEAD
When the hazard lamps are on, the following conditions apply:
• The turn circuit is always open.
• The turn/hazard flasher controls the lamp.
Park/Marker Lamps
Voltage is applied through the EXT LP fuse, to the headlamp switch at all times. Voltage is applied to the park lamps and the marker lamps when the headlamp switch is in the following positions:
• PARK
• HEAD
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.
Stop Lamps
Voltage is applied through the STOP HAZ fuse to the brake switch at all times. When the brake pedal is depressed, the brake switch closes. This action applies voltage through the turn/hazard-headlamp switch assembly to the following lamps:
• The high mounted stop lamp assembly
• The left tail/stop-turn lamps
• The right tail/stop-turn lamps