Explain this to me (electrical gurus)
 

Long time no post, club! question:

I've ripped out the majority of the wires in my current FC project. I am about to wire up the lights (running, turns, brakes, reverse, headlights, etc...).

While labeling the wires to the tail lights (I maintained the light-side of the harness) I found 5 connections:
1. ground
2. reverse light
3. turn signal
4. running lights
5. brakes

Here's my issue: if I jumper a ground wire to ground and power wire to the reverse, turn, or running lights, then I get the relative lights to turn on. BUT if I ground the ground wire and power the brake lights, then nothing happens.

If your first thought is that I step on the brake pedal to use the brake switch (and yes I tried that) keep in mind that I'm "jumpering" directly to the bulbs...and nothing happens with any of them.

Does the stock wiring run a capacitor or something that ups the voltage to the brake bulbs when activated thereby resulting in brake-illumination? What's the deal here?

Your ground wire is not hooked up to the chassis in the harness itself. Maybe you accidentally ripped it out? I would use a multimeter and check your resistance between the chassis ground and the ground wire for the taillights. I bet it is open. if that is the case, trace the ground wire from the tail lights back, and find where it meets the other grounds. If there is a ground that needs to be bolted down, do so. If there is none. You can splice into the ground wire and bolt that splice to the chassis to ground that circuit. I hope that makes sense

I don't think you understand. I'm grounding directly to the connector for the bulb. From battery straight to connector for the bulbs. I'm doing so to find out which prong lights up which lights. All the other lights turn on (running lights, reverse light, turn light), just not the brake light. And this is the case for all 4 brake lights, so it's not a burnt-bulb issue.

Ohm the wires you think are the brake light + and ground - for continuity. Put one prob on the wire you attach to ground and the other in the socket for ground. Continue to the hot side. If this works there isn't any reason why that light is working (other then the bulb itself). The bulbs for the brake light are multi-elemment so you'll need to identify the connector that corresponds to the running, brake, stop lights etc.

You're assuming that the stock harness is still in the car, correct? You want me to check for continuity from + to + and from - to -, correct?

The stock harness (and fuse box as well) are NOT in the car. I'm simply "jumpering" from battery +/- to bulbs' +/-.

Coming off of the taillight is a pigtail for all the lights housed in the unit. It is a 6-wire connector with only 5 slots filled.
1. Black = ground (this is the ground for all of the lights housed in one of the taillight assemblies.)
2. Green + yellow stripe = turn signal
3. Red + yellow stripe = reverse light
4. Green = running lights
5. Red + green stripe = brakes

When I jumper straight from the battery to these connections, all the lights turn on except for brakes.
The same goes for all 4 brake lights, so I'm ruling out the bulb-theory.

Any thoughts?

OOOOOoooookay, so it turns out that every brake light in the car was blown...it literally was the one thing that I thought it wasn't; the bulbs.

In my defense, I've never seen this car running and did not know that all the tail lights were blown before I bought it. Good thing I'm redoing all the wiring, because who knows what would have caused every brake light to blow!