I have a 1994 Ford Ranger 2.3, when the headlights are on, the brake lights stay on as if the brake pedal was being pushed, what could cause this?

First thing to check would be the brake light switch. If that checks out, then check the neutral safety switch. If that checks out then check the combination switch. The combination switch is also called the multi-function switch.

the running lights "head lights" and brake lights are on 2 diff. circuits, so it sounds like you've have one circuit shroted to the other, positive circuit, and running power to the brake lights.
the brake light has it's own ground so all it needs to turn on the brake lights is power.
you'll have to check the wiring over, more than likely it will be in the rear wiring under car.

If two circuits were shorted together you'd have one or more blown fuses. In addition to the problem you are describing, are you blowing any fuses? Are there any electrical alterations, modifications, or add-ons?

fuses only blow with a short to ground, not votlage???

If two voltage bearing circuits are shorted together, the plastic coating around the wires could melt. This could cause the voltage bearing copper wire strands to short to ground (if metal) is nearby and blow one or more fuses.

no, it'd be know diff. than connecting another set of bulbs to a circuit, and with a 20% fault tolerance, you'd never know they were there.

The fault tolerance has only a little something to do with it. Look at it this way. Usin your bulbs as an example, you’ll agree that the bulbs have to get voltage and ground to work right? Ok, so now something goes wrong with the circuit. The voltage bearing line starts to overload and heat up. The thermoplastic wire coating starts to melt. This exposes the copper wire strands. If the exposed copper strands touch ground a fuse is gonna blow, but that’s providing the circuit has fuse protection. If no fuse protection, then a fire could start. Ok, here’s another possibility. Again the same scenario as above, but this time the voltage bearing line “MELTS INTO” the ground line for the bulbs. Again copper wire strands become exposed, but this time the voltage cooper lines, come in contact with the bulb ground line, so a fuse blows. Look man I’m not sayin you’re wrong. All I’m doin here is coverin all the bases, and tryin to be as thorough as I can. Online auto repair remember? Don’t have the vehicle in front of me. Don’t wanna leave anything to chance.

2 more 1157 bulb load on this circuit will not increese amps enough to cause circuit to heat up, amps would still be in 20% range of fuse rating.
now if it shorted to a circuit with a higher amp load, coolant fan, head lights or defroster grid, than yes, it would get hot.
simply ohms law.

did you recently have bulbs put in the tail lights? (putting the lights in wrong could cause this--having them turned around in the wrong direction).

renegade1675,

Tomorrow it will be 4 day's since your last response. Did you resolve this issue yet? If you still need our help, all you have to do is ask.

I'm still thinking that those lights are in wrong (withthe brake light filament turned around to the taillight terminal--causing them to illuminate very brightly when headlights are turned on).