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Jeremy, Certified Diesel Technician/Electrician
Category: Ford
Satisfied Customers: 3323
Experience:  ASE, NATEF Engines and Electrical certified, EPA 608/609
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On a ford 2005 mustang where is the headlight indicator wire

Customer Question

On a ford 2005 mustang where is the headlight indicator wire (I believe lt grn/blk) off the SJB and what would cause it not to be a full 12v?
Submitted: 1 year ago.
Category: Ford
Customer: replied 1 year ago.
It would be very helpful to know specifically which of the plugs off the SJB has the headlight indicator wire and how I could use that wire as a signal wire to a relay. Thus far whenever I turn my high beams on I am unable to get a relay signal indicator off the SJB that the high beams are on other than the headlights turning off.
Expert:  Jeremy replied 1 year ago.

My name is ***** ***** I will assist you with your question today.

I'm an independent contractor and I don't get paid until a rating has been made.

We can go back and forth as needed to help resolve the issue you are having. Follow ups are free after ratings, so rate in confidence!

The light indicator is controlled off the cluster which is computer controlled. The CAN BUS signal from the SJB tells the dash to turn the indicator on or off.

I believe the wire you are referencing goes to the low current board. I will supply the diagrams and the diagnosis checklist for you to go through to try and resolve this issue.

Your lights are computer controlled and if you are getting the lights to work, but the indicator on the dash is not working, there could be an issue in the cluster itself or the communication link to the cluster. You will need the Ford scan tool to do these tests.

CLICK HERE for the folder wit hteh needed information.


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Customer: replied 1 year ago.
Hello Jeremy thanks for the diagrams! They are helpful but I'm not entirely sure it answers my question yet. First let me provide you a slightly better description of my issue. I replaced my engine with coyote 5.0 crate engine from ford racing. There is a specific wiring harness they provide with a smaller BEC unit that cuts out many of the standard wires that came with the original BEC.OK so that is the context. The good news. My headlights and tail lights work. My turn signals and break lights work. The indicator light for High Beams DOES turn on. The problem as I understand it, can be see on diagram 2. Specifically line 1708, which is a LG/BLK wire that appears to go to a relay on the BEC... which I don't have.. I'm assuming that the relay inside the BEC shown on diagram is a standard relay that takes a 12v signal in order to provide power. If that is the case then something is off as I am not getting enough volts from 1708 to signal a standard relay. Am I wrong about that? Would I need a specialized relay in order to get my High Beam Signal from that indicator?
Customer: replied 1 year ago.
Just did some additional testing off the 1708 line and I am getting no voltage period. Is there some sort of additional power source or ground to the SJB that I maybe missing? I see it's suppose to be over 10 at all times.. correct?
Expert:  Jeremy replied 1 year ago.

The 1708 is 5 volts or 2 volts. That is the CAN BUS line and it is a digital signal wire. The signal is pulsed with less than 2 amps pushing the volts through.

If you have no power at all on that, then there needs to be an adjustment done with the PCM through programming. All J1708, 1939, and 2542 wires are computer controlled through parameters on the PCM.

Customer: replied 1 year ago.
Hi Jeremy... I'm confused. The trouble shooting provided from the chilton that you provided listed the LT GR/BLK line of 1708 being always over 10 volts. Am I missing something?
Expert:  Jeremy replied 1 year ago.

You're right. I'm thinking of a 2015. not a 2005...

It's the newer engine that you have that makes me want to think of the newer vehicle.

You are not getting voltage from it and it is still controlled by the internal board on the module. If the relay is good, than the Ford IDS needs to reset the code in it for there is a code shutting that circuit down. A Snap On might due it as well. It needs to be a high end scanner, not the cheap Acron hand held. They won't reset it or even see it. We learned that the hard way in the shops ourselves. They are heavily computer controlled...

Customer: replied 1 year ago.
Thanks for the confirmation. To clarify I have all lights and dash components working. With the exception of the high beam indicator signal. What is especially frustrating is that the white red line that leads back to the SJB from the main headlight switch IS sending low amp power. This is leading me to believe that I must either be missing a required ground OR that I am missing a power supply into the SJB. Do you know which power supply to the SJB would power the high beam indicator signal circuit? As an alternative because I am having to make my on relay do you know of a low powered signal relay that would allow me to shortcut the SJB?
Expert:  Jeremy replied 1 year ago.

It doesn't feed from there. That is fed from the cluster. The SJB sends a signal through the pulses on the CAN BUS to the cluster module. The cluster module sends the signal through the circuit board and activates the indicator that way.

Customer: replied 1 year ago.
Very good info... Do you have a wiring diagram or wire colors that feed to the cluster module and CAN BUS?
Expert:  Jeremy replied 1 year ago.

I added them to the folder already that you clicked on before.

Customer: replied 1 year ago.
Hey Jeremy,
I wanted to let you know, that I'm planning on not rating you. The reason being that I think you did a very good job of providing helpful documentation and customer service (potentially 4/5 stars), but unfortunately you didn't provide me the critical information needed (Soo like 1/2 stars). Specifically the indicator wire for the high beams from the SJB is a ground signal connection not a power signal connection. I literally figured this out through testing every possibility of wiring using the indicator wire identified. Once I found out that the indicator wire was a variable ground connection and NOT a variable 12v power indicator I was able to get the system working appropriately. Anyhow.. I'm torn I appreciate your help and don't want to provide a negative rating, but I didn't get the correct information that I needed.