Brake lights

[Mr. Jones]

Should there be power going to one the wires on the brake light switch?My 350 is frame mounted under the cab.also should it be hot all the time or only with the key on?

[F7BIGJOB]

Unsure on an F350, but the 100 & 250 with ignition 'on'

[Uncle Skip]

One wire to the brake light switch will always be hot.
The other wire goes to the turn signal cam and will over ride both rear turn signals when put your foot on the brake. You should be able to see the stop lights even when the ignition is off.
The second hot wire that goes to the turn signal cam is hot only when the key is on and it controls the front turn signals and the rear turn signals. (each turn light has its own wire from the steering column).

[ICEMAN6166]

sorry hate to say this but brake lights only work with ignition on.at least with the pressure type switch
it is possible to change this by changing the wire on the back of the ignition switch from the on to the battery feed (center)
terminal.

[Toyz]

Annnd, while we're picking on you The brake lamp does not override the turn signal, the exact opposite is true. AAAAnd, the rear turn signals share the wire with the brake lamps on each side. I would suspect the un-common setup of only working with key on is due to the tendency of the pressure-actuated switches to stick and thus potentially drain batteries and damage lenses. Once hazard lamps came into common (mandated) presence on light vehicles, I believe all went to full time hot, probably to simplify the hazard circuits. You may have noticed that with flashers engaged and turn signal also engaged with key off, many systems thus became "three way flashers"
Paul