Im having any issue with my rear tail lights. To date i have replaced the bulbs the round flasher under the dash and the turn signal selector in the steering column. Each blinker works and both brake lights work the problem comes when you step on the brake and use the right blinker the blinker works but the left brake light does not work. Along with that the light in the dash showing the right blinker stays solid as soon as you take your foot off the brake all is good. Again this only happens when you you use the right blinker and the brakes at the same time. What can this be!!!!!!!!!!!!!!

My first thought is to make sure you have a good ground(s).

Yep, either grounds or a set of dirty contacts in the bulb sockets.
Clean the sockets up, check the grounds, put in some bulb grease and it should be fine.
Ron

Guess i will try that, to think when i was at the store getting the bulbs the girl asked me "u need any grease" i said naaaaa. Guess im going back lololol

One last item, you can clean the contacts with a pencil eraser! it works real well unless the contacts are pitted a lot.

Ron

I checked everything and heres where im at all blinkers and brake lights work fine seperatly the problem comes in when u brake and have the right blinker on. what happens is the right blinker stays solid and the left brake light doesnt turn on. I replaced the flasher under the dash is there a second one in the car if so where might i find it.

Make sure the grounds under the dash are good.

Make sure you are getting a good ground at the tail light assembly also. I replace those plastic bulb sockets with metal ones and waaaalaaa solved the problem.
I got metal sockets at the local auto parts store. For a Ford....I know.....but they get a better contact then those plastic ones with a little metal finger.

Not so sure its a problem in the socket because they work fine using either the brake light or the blinker soley but when u try to combined is when u run into the problem

Probably a bad turn signal switch.
The power to the brake lights are fed through the turn signal switch; when you flip the switch right or left the power to that side brake light is interrupted so power can be fed from the turn signal relay instead. If the circuit in the switch that interrupts the brake light power is bad, the problem you're experiencing is is exactly what happens.

65ragtop396 beat me too it...I was going to say the same thing. I had this exact problem in my '68 C-10

If your referring to the switch in the column its brand new just put it in last week

If your referring to the switch in the column its brand new just put it in last week
The question then is, did the lights work as they should before you changed the switch?
The new switch might be wired incorrectly. Also, just because something is new doesn't mean it'll work properly, I've seen that way too many times with the Chinese made aftermarket parts.

No the same problem was there i changed that trying to eliminate possible causes

John its a 1971 chevelle

Just a thought, do you have the proper bulb in the socket? I've seen people install a two-element bulb where a single-element should be and vice-versa. It makes weird things happen. It's the difference between a 1057 and a 2057, or something like that. It's been a long time since I worked at the parts store and I forget the numbers.

The bulb is #1157

Hazard flashers work?... all 4 corners & dash indicators?

Yes everything works

I'm still thinking turn signal switch.

One of the contact fingers isn't moving/making/breaking contact correctly..... anyone else?

I agree with John D, the switch should break the contact for the light when blinking off, then contact when blinking with brake light brightness(not taillight brightness, which is half as bright).

It almost has to be a switch problem since everything else works fine independently. What you're really doing is making and breaking contact in constant succession with the switch. Things are bad sometimes, even when new....fuel sending units for example.

I'm betting on a bad ground on the light socket. You should have two wires to the light socket. One wire is for brake and signal. The second wire is for tail lamps. The socket is grounded by the screws that mount it to the body.
If you lose the ground to the body and turn on the tail lamps, the tail lamp wire gets 12v, and the brake wire gets ground so current can flow through both filaments in the bulb and it will light. If you use the brake and have the tail lamps off, the current is reversed. The brake wire gets 12v, and the tail lamp gets grounded so again current flows through both filaments and the bulb will light. In both of these situations, the light should be dimmer than normal because the 12 is shared through 2 filaments instead of lighting just one.

Now, when you turn on the tail lamps and step on the brake at the same time, both wires get 12v. With the body ground missing, the bulb can't light.

Possible....

We need more diagnostics. What happens to the turn/brake lights when used with the taillight circuit on?

Sounds good, Gary but here's my issue with that.....
I just tested my brake and turn signal lights for the first time last weekend since I've had my car and the steering column back in. New wiring harnesses throughout except the steering column and intermediate harness. Plastic taillight bulb housings, painted taillight extensions....no direct metal to metal contact for a ground tang and they work flawlessly, bright even especially with LEDs.

This is why I think it's the switch.

Plastic taillight bulb housings, painted taillight extensions....no direct metal to metal contact for a ground tang and they work flawlessly, bright even especially with LEDs.

This is why I think it's the switch.

Do the sockets have 3 wires or 2? If only 2 wires, the ground has to come from the mount. If it has 3 wires, then one of them is the ground and my idea is wrong.

I'll have to check but I think there's 2 wires.....when I plugged them in with the bulbs, this very situation actually crossed my mind. Since they work just fine, and I've not scraped any paint off for ground contact, I'm thinking one of the wires turns to a ground when the turn signal is engaged.....although that may not make sense since if your brakes and turn signal are both on, one of them cannot become a ground.

Hmmmm....will have to look.