I have a 2008 f250 xl with the 5.4l and 6 speed trans. Issue I'm having is the brake warning light comes on along with the check brake system on the display in the cluster. Then the headlights start flashing. I've checked all the fuses and even replaced the battery and the headlight bulbs. Never had an issue like this. Any help???

 

The first concern would be to determine why the brake warning light is coming on. The light pulsing , do they just go slightly dimmer or do they go out completely?
We don;t know at this time if there is a poor connection somewhere in the electrical system or possibly a control issue.

The problems could very likely be related to a malfunctioning module.
I would suggest that you have your vehicle checked for fault codes in the vehicle computer. Places like Autozone will usually do this for you at no charge. Get the codes and post them here. Depending on what they are, we hopefully will be able to offer some useful suggestions. Are there any other features that may not be working correctly at this time ?

 

The lights dont go out. They flash. They get bright then dim. When this happens you cant flip to high beams, and the blinkers stop working. I had the codes read at an auto zone and the only code it had was for an o2 sensor. I unplugged the alternator and the flashing stops. But the brake warning light stays on. Is it possible that the alternator is overcharging and causing a module to break down?

 

Here's the kicker. If you unplug the battery and let the computer clear over night, the issue goes away. But occurs after driving the vehicle. And it doesnt always have to be driven. It's so scattered and unpredictable it doesnt make sense
So it almost has to be a module doesnt it?

 

I would suspect to start with, the alt has a problem, but needs to be confirmed.
The part of the lights going dim could indicate an excessive power drain maybe an intermittent short circuit.
Some detailed testing needs to be done to confirm.

 

Hello Louis5289, You most likely have a bad voltage regulator which is an integral part of your alternator. I used to change the voltage regulator but its such a pain and with the age of the vehicle I would just replace the alternator. This should cure the problem. As an additional thought I have seen a bad battery with a shorted cell that would start the vehicle but produce all sort of electrical issues. You may want to have your battery checked.

 

I have replaced the battery. What makes no sense to me is that I can unhook the battery over night and it cures the problem for a little while. I will replace the alternator and see what happens from there. What testing needs done to check those 2 modules and where are they located?

 

Also when this happens. You cant switch to high beams and the turn signals dont work

 

The best way to check the modules is with a capable scan tool.
Module could be malfunctioning , but a good place to check would start with the multi-function switch on the steering column.

 

Okay I will let you know how it goes. Thanks for the help!!!