About two weeks ago I asked about led's for a third brake light.I have a third light from a 1986 Corvette .I found a sight through E-bay(www.hid-lights.com,in case someone is interested) and bought a rope with 36 lights in it.Works and is plenty bright.Once it's hooked up,the brake light (driver side) dims to about 1/3.The third light doesn't change in intensity.Followed the instructions in the thread about the third light (tapped into the left side brake wire) and this is my result.Should I go direct to the brake light switch and run an extra wire?
Thanks in advance.

Should not have to.

Check your bulbs. Over the years the bulb contacts get worn down and shake around a bit thus causing intermittent contact. Start there.

If that does not help check the contacts on the fuse block. Make sure they are clean.

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The brake light(wiring) comes in on the drivers side. If this third light draws alot of amps or you have impeded the flow to the left brake light, that could cause the dimness. But bulbs are cheap and your labor is cheaper so try above mentioned process first.