I am using a 12v test light. Probe to the power wire, other to ground on the vehicle. Using tire iron to wedge between the brake pedal and the seat.

I am not getting power to the 3rd brake light. Bought a new light strip, plugged it in and nothing. Thought maybe it was defective, so got out the test light and tested the yellowish/white wire and no power is getting to the brake light. Are you saying I need to probe the black wire and yellow wire at the brake light connector where it plugs in at?

The more I think about what Richphotos is saying about tapping into the brake light switch to get power is confusing me. Why would I not be able to tap into the white wire near the tail lights instead of getting it from the brake light switch itself? If there is a white power wire at the switch and also at the tail lights, would I not be able to tap it there? Or does the turn signals somehow get routed and run back to the white wire at the tail lights?

Sorry I am making this more difficult than it needs to be.

These last two pictures were borrowed from the thread I posted about the Euro tail light thread showing where he tapped into.

 

No you are using the test light correctly, I forget what wire is power on the brake light but that is testing the voltage not current that is why I got confused. one of the wires should be probed and the should be grounded ( make sure it has good contact with bare metal).

I'm not to fimilar with what richphotos is talking about because I didnt have that problem with mine but it makes what he said about it blinking when you directional is on.

You might have a pinched wire somewhere and grounding the circuit out.

You could always test that wire with the probe and put your directional and see if the test light blinks. If it does you would have to run a new most likely and if doesn't blink and turn the test light on only with the pedal then use. That's what I would say.

 

I was talking about it blinking if you were to tap into the passenger side or drivers side brake light to get the 3rd brake light to work.
Since there are only 3 wires per socket on the brake light sockets (brake/signal, running, and then ground) Each time you would turn the signal on for the side you tapped into, the 3rd brake light would start to flash.

Finding a short by checking ohms ect, would tell you if there is a short, but after that, finding where the short is, would be more trouble than just finding 10ft of 16 gauge wire and tapping into just after the brake light switch under the dash.
Most of the time they run the brake light wires through the body panels up to the front. You would have to basically pull apart your whole interior on the side the 3rd brake light power wire runs up.