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Daryl, Shop Owner, Master Mechanic
Category: Ford
Satisfied Customers: 12549
Experience:  28 years experience, Master Mechanic
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Ford F150 STX: Brake light comes on but not the ABS light

Resolved Question:

The dash brake light is always on in my 2004 F150 4X4, but not the ABS light. I have replaced all 4 disk brakes pads, 4 rotors, two new calipers, new emergence brakes, and new parking brake switch (twice). I also replaced the master cylinder float switch with a new one from Ford, then replaced the entire master cylinder with a new float and switch. I have bled this system over 5 times with a liter of fluid through each caliper. The fluid coming out is as clear as the fluid going in and not a pin sized air bubble anywhere. All parking and three brake lights are working. I disconnected the battery several times to reset the computer. The pedal pressure is so high if you just tap the brake then you’re hitting the steering wheel. Thanks in advance.

Submitted: 5 years ago.
Category: Ford
Expert:  Daryl replied 5 years ago.

I would start by checking the parking brake switch. If it is disconnected and the light goes off that is the problem. I was also wondering if you actually checked for a short or are just assuming there is not one. I have seen the wires from the float in the master cylinder short out before and cause that light to be on.

Customer: replied 5 years ago.

Thank you for your reply.

The parking park switch cannot be the issue. The light does not go out with the switch unplugged. I have two of these trucks and I have switched the brake switches with the same results. The 04 light stayed on and the 05 wasn’t. I even bought a new switch from Ford which didn't put the light out either. The switch can be fully pressed in by hand so it does not contact with the emergency brake pedal. As I said the float level switch has been changed three times. The plug is good and sound and the wires appear clean and separated. Playing with all the wires and looms will not make the light blink.

What about the ABS box with the motor? I was told this could bleed through the wheel cylinder.

Expert:  Daryl replied 5 years ago.
If the brake is good and pedal is hard the problem is not bleeding, its most likely either the instrument cluster causing the problem or there is a wiring problem, I have not ever seen the ABS cause this without the ABS light being on as well. Here is what I would do if I were trying to fix this, check the 2 wires from the brake fluid level switch for a short to ground between pins 2 and 3 of C220a of the cluster. Also check the Light Green/Red (LG/RD) wire from the parking brake switch for a short to ground to pin 24 of C220a of the cluster.
Customer: replied 5 years ago.


I have more questions, so let's start with the simplest: The LG/Red parking brake switch. Do you want me to connect LG/Red to the C220a pin 24 with an ohm meter? The C220a, is that the plug at the end of the wiring harness (now not connected to anything) or part of the dash board? Should I connect the LG/Red wire to a body/battery ground and get 100% or something less?

If it is the wiring harness plug, assuming I can get it unplugged, is number one the top left and number 2 next to it on the right, or the row below number one? Also, when looking at the plug, (I haven't seen it yet) would the locking thing be on the bottom or top?

I understand electronics I just need a little clarification.
Thanks for your patience.

Expert:  Daryl replied 5 years ago.

To check for a ground with an ohm meter I would take the connector off the cluster and connect one terminal of your ohm meter to ground and the other to the pins described. There should not be a reading but if there is that can be causing the light to come on. Below is a pic of the connector -


Customer: replied 5 years ago.

This morning (26F) I started my 04 F150 and the brake light went out. I let it run for 5 minutes with the heater on and then used the emergency brake 12 times and the light reacted as it should. I have to use the brake to put it in gear but only tap the pedal a 1/2 inch to put brake lights on. As soon as I touched the pedal with no pressure the cluster brake light came on. Also the low fuel message came on. I just put $20.00 in before I parked on Wed.

Next I tried to find the C220a connector. I couldn't reach it by following the loom as far as I could while reaching up under the dash. While I tried feeling for it with one hand I held a mirror with the other hand a saw the light blink once. With more wiggling of the loom, as high as I could reach, I was able to finally "put the light out". The fuel gauge also reads ¼ tank with no message.

So, while I haven't fixed the problem, I know it's the connection to the cluster or a circuit board but not anything under the truck. It also isn’t the emergency switch or the level switch.

I have only one more question and then I will accept your answer in return for your help and time. I have the details on how to disassemble the dash to remove the cluster. My question is: if I remove the cluster and disconnect the C220a will that have an effect on the PATS if I reconnect all the original equipment?

Expert:  Daryl replied 5 years ago.

No. Removing the cluster and then replacing it will not affect the PATS system at all.

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