dgheinen

my 78 SAE Vette is running great and most everything works; except when I have the headlights on, the right turn signal is very slow and the brake light is dim. ESPECIALLY when the brakes are applied. What could this cause be? I've cleaned up the ground (located on the rear left of the body, near the left brake light area). Any ideas? Appreciate it greatly!

Btw, all bulbs are brand new, everything else works great, etc. (Well, not my under hood bulb!)

MelWff

It sounds like a ground issue, do you have the chasis wiring diagram, are you sure the left side is the only ground?

Uncle Maddog

Each bulb socket has a ground terminal as well, and they corrode or even break. Check them all with a test light or a meter. I also found a wire to a parking/ts light pinched flat and bare by a bumper bracket, which "bled off" power when activated. Good luck!!

lionelhutz

Is the tail light brighter as well? If you changed sockets or fixed some wiring then it's possible you have the wires backwards with the turn/brake wire going to the tail light element in the bulb. This makes the brake/signal dull and the tail bright. I've seen this swap done many times when people are re-wiring a vehicle or trailer.

JohnRR

I think you're saying that all the turn and brake lights work properly when the headlights are off. Then, when you turn the headlights on, bad things begin to happen. If this is what you're saying, then it sounds like you might be having a voltage drop issue caused by the high current demand from the headlights. Check the voltage at the brake lights before and after the headlights(high beams) are turned on, and report back.

John

hugie82

My 82 is doing it too and my volts are at 13v. When I turn the headlights on the right blinker either blinks erratic or doesn't flash at all.

JohnRR

Are you reading the 13 Volts on your dash gage, or did you actually take a measurement at the right hand brake light bulb?

snike3

I know this thread is almost a year old, but has anyone figured out a solution for this? I'd be interested to hear anything that fixed your guys' issues.

I'm in a similar boat... I have all brand new wiring harnesses so I know the wires and contacts are good. Everything works perfectly with the headlights off, but as soon as the headlights are on the blinker doesn't work right (I think maybe just the right). I haven't checked the brake lights yet.

JohnRR

Snike,
When you say that you have all new wiring harnesses, did you replace the harnesses on both sides of the firewall? I mean did you replace the 'Fuse Block/Dash Harness' and the 'Headlight Harness'? All the power for all the lights pass through the fuse block junction. If these connectors are not perfect, then when the high power headlights are on there will be a large voltage drop at the fuse block. This doesn't leave much left for anything else.
Do both the left and right turn signals malfunction when the headlights are on? Does it get worse when your high beams are on and when you step on the brakes?
One way to reduce this voltage drop is to install a relay system to operate your headlights. This will eliminate all the headlight power from passing through the fuse block and headlight switch. See Speed Direct for an easy to install kit.

John

snike3

I did a complete wiring harness kit and then did more... So I have brand new headlight, engine, dash, tail light, and power window harnesses. The A/C hardness just got thrown out because I got a Vintage Air setup. I even went as far as to replace the main battery cable and grounding cables/straps. There isn't a single bit of old wiring left in the car.

As far as behavior, I really haven't gotten to test it too much yet as I've been debugging some more major issues. I'd go check the behavior a bit but it's currently in the shop getting the new suspension aligned. If I remember right it was just the right signal that had issues, but I'm not certain. And I hadn't tried the brights yet.

It's kinda funny that you mentioned the SpeedDirect nevernight kit. I was trying to convince my wife that should be the next project to under take. They look very promising. The original lights are kind of pitiful. They're almost like strapping a pair of flashlights to the front of the car.

Tim

budco

Dim bulb is always a grounding problem.

JohnRR

The wiring in my '73 was a total mess. Like you, I also replaced every bit of wiring and now everything works. The SpeedDirect kit works well and is very easy to install.
The grounding issue that Budco is referring to brings up a good point too. Make sure your battery grounding cable is making a clean contact with the frame. I used some "Ox-Guard" grease to insure the bare metal contact points stay corrosion free. I also installed the short ground cable that goes from the front frame to the engine block by the starter. When I had the dash apart, I ran an extra ground wire to the gage cluster.
Let us know about the testing when you get your car back home.

John