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powerstroker24
powerstroker24, Master Diesel Technician
Category: Ford
Satisfied Customers: 255
Experience:  11+ yrs diesel exp. Ford Master Diesel certified. ASE L2 Advanced Diesel Diagnosis cert., ASE T2,T6
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f-250: my head and dash lights pulse bright and dim..diesel 4x4

Customer Question

my head and dash lights pulse bright and dim slightly while driving. 03 f-250 diesel 4x4 7-3L. Bought truck 6 mos. ago has orig. alternator think this is problem ?
Submitted: 5 years ago.
Category: Ford
Expert:  powerstroker24 replied 5 years ago.
Thanks for your question and I will be glad to help. Do you have access to a multimeter? Also does the battery light illuminate? Have you been having issues with the truck starting/cranking slowly?
Customer: replied 5 years ago.
seems to crank fine, no battery light comes on at all. But took truck in to have windows tnted awhile back and they said they had to jump start it. Have not had any problem since. it might be the batterys also ? have a multi meter, not really sure how to use it.
Expert:  powerstroker24 replied 5 years ago.
Okay basically turn the multimater to the (V) voltage setting the one with the straight lines not the squigly one. You will know you are on the right setting when you connect it to the battery and it reads around 12.00 volts. Obviously you will need to connect the red lead from the meter to the red lead on the battery and vise versa for the black lead. Start the truck and let it run for 2 minutes and then take a voltage reading. Let me know what you find, thanks.
Customer: replied 5 years ago.
seems to be 12 volts on meter ?
Expert:  powerstroker24 replied 5 years ago.
With the engine running? It should charge at least 13.4 volts with the engine running. I can give you some circuit checks to do if you are comfortable with this or you can simply remove the alternator and have it tested. Most likely you will find it is a faulty alternator but if you want to perform the checks instead of taking the alternator to a parts store then that is ok too.
Expert:  powerstroker24 replied 5 years ago.

The pics might not show on your end but just use the wire colors,and make sure to follow the instructions exactly, thanks.

 

 

 

 

 

 

Test Step

Result / Action to Take
B1 CHECK GENERATOR B+ CIRCUIT 36 (YE/WH)
  • Measure the voltage between generator B+ terminal, circuit 36 (YE/WH), component side and ground.
  • Is the voltage equal to battery positive voltage (B+)?
Yes
GO to B2.

No
REPAIR the circuit. TEST the system for normal operation.
B2 CHECK GENERATOR GROUND A CIRCUIT 35 (OG/LB)
  • Disconnect: Generator C102a.
  • Measure the voltage between generator C102a pin A, circuit 35 (OG/LB), harness side and ground.
  • Is the voltage equal to battery positive voltage (B+)?
Yes
GO to B3.

No
REPAIR the circuit. TEST the system for normal operation.
B3 CHECK I CIRCUIT 904 (LG/RD) FOR AN OPEN
  • Disconnect: Generator C102a.
  • Ignition ON.
  • With the ignition switch in the ON position and the engine off, measure the voltage between generator C102a pin I, circuit 904 (LG/RD), harness side and ground.
  • Is the voltage equal to battery positive voltage (B+)?
Yes
GO to B4.

No
REPAIR the circuit. TEST the system for normal operation.
B4 CHECK FOR VOLTAGE DROP IN B+ CIRCUIT 36 (YE/WH)
  • Start the engine.
  • With the engine running, turn the headlamps on, rear defroster on, and the blower motor to the high position.
  • With the engine at 2,000 rpm, measure the voltage drop between the generator B+ terminal, circuit 36 (YE/WH), component side and the positive battery terminal.
  • Is the voltage drop less than 0.5 volt?
Yes
INSTALL a new generator. REFER to Section 414-02.

No
REPAIR high resistance in the B+ circuit 36 (YE/WH). TEST the system for normal operation.
powerstroker24, Master Diesel Technician
Category: Ford
Satisfied Customers: 255
Experience: 11+ yrs diesel exp. Ford Master Diesel certified. ASE L2 Advanced Diesel Diagnosis cert., ASE T2,T6
powerstroker24 and 8 other Ford Specialists are ready to help you
Customer: replied 5 years ago.
sounds good, lets check circuits
Expert:  powerstroker24 replied 5 years ago.
Okay let me know what we find. If you get to step 4 then we are looking for almost no voltage. This is to eliminate a issue with the battery connections and the main feed to the alternator(should be .10 or something below .50 volts).

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