Good advice re the stoplight. Not sure how to check with a multibmeter - continuity light? but will trouble shoot.
One pin on the stoplight switch (doesn't make any difference which one) should have battery voltage all the time. Operate the switch's lever and make sure that the voltage doesn't change more that 1/10th of a volt. If the change is more than that, the problem is a poor connection between the switch and the battery. Fix that before continuing.
The other side of the switch should have no voltage until you press on the brake pedal (or you move the lever). Then it should have battery voltage. If so, and the brake lights do not come on, the problem is in the wiring from the switch to the brake light(s), the brake lights themselves or the ground to the brake lamps.
If the voltage is a volt or more less than it was without the switch "on" the switch is bad.
