when i try to start the vehicle the brake light comes on
e-brake switch, low brake fluid, possibly bad gauge cluster (they develop shorts in the wiring), check out f150online.com, they have a few topics on this problem, with most reporting it is the gauge cluster causing the problem. You can pull it forward and play with the connectors in the gauge and see if that affects the light, if it gets a ground it shouldn't be it'll turn on. But do that after checking your brake system for any actual faults.
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