Since my 2nd body off on my '69 I haven't been able to get my tail lights working again.

-Doesn't look like any fuse is blown.
-Nothing in the rear works(tail lights, side blinkers...)
-Front lights work fine.

Turn signals don't flash, just on(front) or nothing(rear)


I think this is also connected to my LS1 swap electrical problems. Any time a light/brake/blinker(all get power from orange wires) everything electrical primes with the LS1(fuel pump, injectors, maf? ...)
Pretty sure it's a backfeed of power through grounds but I've got plenty of grounds from what I can tell.

 

This really should help you understand how the lamps work.. and help you solve the problem. I hope.

Most people don't realize the stop lamps go through the turn signal switch and/or how it works. The lamps are fed power on two wires.. One is the (both lamp) power and one wire is the turn only power. So in a nut shell... When you hit your brake lamps the power form the switch goes to the turn signal switch (not the rear). If you have the turn signal switch in the neutral position then power goes out to both lamps (green and yellow below). But if you have a turn signal on.. the power from the white wire is cut and switched to purple power wire (which has the flasher) for the side you are turning on.

So with this in mind.. you should start some diagnosis...

1) Always verify you have power coming out of the brake lamp switch or white wire.
2) Verify power on the purple wire at the flasher.
3) Place a jumper in line for the brake lamp switch (testing takes time) and disconnect your distributor power wire (save those points).
4) Once you have the power jumped at the switch then go to the turn signal switch and see if you have power at H and E in the diagram below.
5) If you have power at H and E without the turn signals on you should have power coming out on G and F below. If not then take a hard look at the connection for the t/s switch..
6) Test the flash.. turn the lever to one side or the other and test to see if power is pulsing on either F or G depending on side.

If all this works.. then I would go to the back of the car and start working forward by testing the grounds at the taillamps and pinging the wires. The rear harness connector can sometimes be the culprit too.

Hope this helps you Punisher.. if you need more post back.. signing off for the night though..


Willcox

 

Thanks. I'll try to dive into this hard tomorrow.

My center console isn't in... could that be causing issues with anything?
I only ask because really I never touched any wiring related to the rear lighting. So I find it strange they're not working anymore.



No distributor anymore with the LS1 so not sure about the bypassing step #3.

 

The shift console should not play an issue. Make sure the connector at the bottom of the column is not loose too.. that would cause you all kinds of issues.

You'll still need the jumper between the two wires at the brake lamp switch in three..

LS1 huh.. I hate points too.. LOL..

 

Replace it anyway. I've seen fuses which looked good until you pulled them out into the light of day and could see the burn.

Check the rear harness ground on the frame. Good contact is required.

Ensure the rear harness is plugged in well to the main dash harness.

 

I ground down to bare metal on that rear ground thinking that was my problem since I powdercoated the frame. But I'm pretty sure it's making good contact now.


The fuses are my first thing to check this morning. Taking each one out to inspect. Wouldn't know which one to replace... DIR SIG, Tail lights, stop....

 

This a quick brake light circuit check I use to check operation of the brake light circuit.
1. Turn on the hazard lights, they will flash the indicators on the dash.
2. Depress the brake, the flashing will stop, but the indicators will remain on, with no flash.
If this works the problem is down stream from the switch.
The brake switch circuit overrides the T/S & Hazard circuits.

 

I actually didn't mind the points...it was the carburetor I didn't want to touch lol.

Trying to get all your info straight from your first post. I need to bridge the white wire from the brake switch and the purple wire right before the flasher? Or is it saying to bypass the brake lamp switch altogether and give direct power to the white wire?

 

That's what happened. Hazards flashed, applied brake=solid lights.


So what's down stream that I can check seeing that my brake switch is working.

 

Start at your rear lights and work toward the switch,checking connectors and double check the grounds at the rear.
Is the lights the only things not working in the rear? Is there anything any where else not working?

 

Well. Figured it all out!

After the LS1 swap I never hooked up the old fuel pump wire as I was using the F-body pump. Hooked up what looks like just a black ground wire to the pump and all the issues went away.

I thought that wire was power for the pump but now i remember the pump was on the motor and according to the wiring diagram it's just another ground I never had hooked up!

lesson learned!

weird how all those issues are caused by one tiny little wire.

 

Good deal....

Just in case others see this later.. You jumper the brake lamp switch. This will put power on the white wire so you don't have to keep pushing the pedal.

In some cases you can start from the rear but when the customer states there is a turn signal issue more times than not it's something in that area instead of in the rear. When turn signal pups out I go to the source and work backwards.

IMHO,

Willcox

 

 

I have a question 68 with same issue, tail lamp bright on left side, yet the voltage to each measuring the same at 11.9 volts. New lamp housings, grounds replaced, where is the differential in intensity coming from if the voltage is the same?

 

Your description of the circuit helped me resolve a ground short in my turn signals. Appreciate you taking the time to share your expertise.
Aldo Jackson '69 Coupe

 

An old thread with good info:
So i'm now having the same issue, NO BRAKE LIGHTS every other light, & signal work perfectly. when i put on my hazards, they both flash in the rear & on my dash both green arrows as well, I hit the brakes & nothing changes.
Dash still flashes left & right green arrows & the rear light both sides still flash. Hitting the brakes does nothing ! I'm next going to check the bulbs, thats easiest & cheapest. I may also have a ground issue because in the past some lights were brighter then others & other flashed faster or slower then others. Where is the main rear connector all are talking about ?

 

ttt

 

Follow the diagnosis provided in the thread above

 

Jeeeez, why didn't I think of that ?? ....................because my flasher symptoms were different then what was posted !

 

You need to start a clear new thread then, that shows you followed the steps Willcox have provided - and what were the results of those steps you took.

If you have not done the diagnosis - which it seems may be the case...no one here is going to be able to do that for you unless they are on the same street as you...

Those steps (in the write up) are golden and have solved the issues each time I've been down this road with a C3 and I am sure 100s more...