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We've recently had some issues with our 76 tail lights. At first, just the directional lights went out. Now that we've started troubleshooting we've discover none of the back lights work (brakes, hazards, back up). We have checked the fuses, and they all have power except the mist lps. We don't think it could be the bulbs because it's all the back lights, including the back side blinkers. Is there a simple solution we could follow that doesn't include ripping apart the interior?
Anytime I come across some GREMLINS, or things that act strange, I usually go to the ground connections first. And welcome aboard the forum and your first post. Now we need some info. Tell us about your car, how long have you had it and a picture would be great.
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Hi and welcome
Make sure that the correct bulbs are installed, then attach a wire to a good ground and touch the other end of the wire to the brass part of the bulb holder.
If the bulb lights up, then check for a bad ground.
Make sure that the correct bulbs are installed, then attach a wire to a good ground and touch the other end of the wire to the brass part of the bulb holder.
If the bulb lights up, then check for a bad ground.
My two CENTS. If the bulb holders look NATSY then spend some time cleaning them, sometimes Bubba has pushed the bulbs in the wrong way, and caused the plastic holder to become warped … allowing the bulb to be inserted the wrong way. WELCOME ABOARD
Like Kanvasman suggested it is most likely a "ground" related issue that is plaguing your Corvette's rear lights. I would start in back and verify that you have a good ground connection to the tail lights. Since it affecting several lights it might be a branch connection in the ground system for the rear of the car.
I cleaned the sockets with DeOxIt electrical connection cleaner and the tail lights became "slightly" brighter after the terminals were cleaned in the sockets After 58 years of being on the road my C3 tail lights were not getting 100% of the power into them so they put out a little less light. After cleaning one side and checking after dark outdoors, it was plainly obvious which side had been cleaned. Now I clean every light socket I come across as well as any other major electrical connection. DeOxIt removes all corrosion simply wiping it off. If you don't have an DeOxIt (available on Amazon) you could use a #2 pencil's eraser and gently erase the oxidation away. This is a gentle way to clean the connection or socket.
On one instance we had a Forum member who used Die-Electric grease on the bulbs and then had problems. Die-Electric Grease IS NOT CONDUCTIVE and if it is used in between the bulb and the socket the bulb will not light up properly because the grease blocks the power. The same goes for Spark Plug wires where somebody puts it inside the Spark plug wires cap and the engine starts missing on that cylinder. One guy used it on every battery connection, kind of strange that he had issues right away...
Die Electric grease is used to lubricate the inside edge of the spark plug boot to keep the boot from sticking to the spark plug's porcelain and potentially breaking the spark plug wire when it is pulled on or being removed.
This is another place that a tool called a Power Probe could really make the job MUCH easier. The P.P. 4 has an LCD screen which reads out the voltage at the connection you are touching the tip to. If you want 12 Vdc at the tip you roll the rocker switch one direction, If you need a ground you simply roll the switch the other way and you will have (0 Vdc). The tool uses the battery power to operate and has been one of the best tools I have for working on the electrical system. I used it on my C4 as well, the fuel pump was not running but I was able to quickly find that with full power the fuel pump ran fine. Then you go to the next connection and follow the voltage drop until you find it's source. On my C3 I was able to start at the window motor that was not working, after applying 12 Vdc to the motor directly at the harness connection I was able to see the motor worked fine when powered up which meant that was not the issue. This tool is awesome, I just wish they were less expensive so more people could enjoy all the benefits of having and using one.
P.S.
If reading a schematic is hard then you might consider getting in touch with DocRebuild who sells a nice set of laminated Wiring Guides showing the path of the power which is a bit different than a schematic. He also sold me a chart that shows all the connectors used in the Corvette so you can identify a connector and know where it goes. I believe they are called the oSoEZ wiring guides for 1958-1977 Corvettes
Last edited by ctmccloskey; Mar 4, 2025 at 10:09 AM.
Like Kanvasman suggested it is most likely a "ground" related issue that is plaguing your Corvette's rear lights. I would start in back and verify that you have a good ground connection to the tail lights. Since it affecting several lights it might be a branch connection in the ground system for the rear of the car.
I cleaned the sockets with DeOxIt electrical connection cleaner and the tail lights became "slightly" brighter after the terminals were cleaned in the sockets After 58 years of being on the road my C3 tail lights were not getting 100% of the power into them so they put out a little less light. After cleaning one side and checking after dark outdoors, it was plainly obvious which side had been cleaned. Now I clean every light socket I come across as well as any other major electrical connection. DeOxIt removes all corrosion simply wiping it off. If you don't have an DeOxIt (available on Amazon) you could use a #2 pencil's eraser and gently erase the oxidation away. This is a gentle way to clean the connection or socket.
On one instance we had a Forum member who used Die-Electric grease on the bulbs and then had problems. Die-Electric Grease IS NOT CONDUCTIVE and if it is used in between the bulb and the socket the bulb will not light up properly because the grease blocks the power. The same goes for Spark Plug wires where somebody puts it inside the Spark plug wires cap and the engine starts missing on that cylinder. One guy used it on every battery connection, kind of strange that he had issues right away...
Die Electric grease is used to lubricate the inside edge of the spark plug boot to keep the boot from sticking to the spark plug's porcelain and potentially breaking the spark plug wire when it is pulled on or being removed.
This is another place that a tool called a Power Probe could really make the job MUCH easier. The P.P. 4 has an LCD screen which reads out the voltage at the connection you are touching the tip to. If you want 12 Vdc at the tip you roll the rocker switch one direction, If you need a ground you simply roll the switch the other way and you will have (0 Vdc). The tool uses the battery power to operate and has been one of the best tools I have for working on the electrical system. I used it on my C4 as well, the fuel pump was not running but I was able to quickly find that with full power the fuel pump ran fine. Then you go to the next connection and follow the voltage drop until you find it's source. On my C3 I was able to start at the window motor that was not working, after applying 12 Vdc to the motor directly at the harness connection I was able to see the motor worked fine when powered up which meant that was not the issue. This tool is awesome, I just wish they were less expensive so more people could enjoy all the benefits of having and using one.
My husband is going to try and locate the ground connections today and see what he finds. The lights all worked initially, so we thought it might be a fuse. Hopefully it will be a simple ground wire issue. Thanks for all the information! If only tools were cheaper, but they want you to bring cars to dealers so they can make all the money.
Hopefully, it is just a loose connection! These older cars have been out in the weather for a long time and we need to expect little problems. It is not likely this problem will cost very much to repair. If you need help I would find a Automotive Electrical shop near you and have them help figure it out if your husband doesn't have any luck. But honestly, I don't expect it will get that far as your husband will find the problem and resolve it!
Maybe you might buy him a Power Probe for Fathers Day or some other occasion. One of those tools makes it so much easier to find the problems and an aspiring Corvette mechanic will probably benefit having one in his tool box.
If you took a C3 to a Chevrolet Dealer they wouldn't know what to do. The Corvette mechanics are so used to the cars telling them "what to replace" that they have lost the troubleshooting skills they need to have. Back 30 + years ago I took mine for a differential/posi-trac rebuild. I warned the advisor that my car was very "quick" and the brake VERY sensitive, so be careful with my toy. A few minutes later I watch as the mechanic took my car flying across the parking lot and slid to a stop at break neck speed. He did not have his seat belt on and he almost hit the windshield when he stomped my "Sensitive Brakes". The older BB Corvettes are dangerous in the hands of some people.
Let us know when your husband has the issue solved. Then tell us what he found so we can "all learn" from this experience of yours.
On youtube there is a user by the name of “Problem Solver Garage”. If you look under his playlists you’ll see a series titled “Corvette C3 restoration”. His videos are great at showing how to weed out gremlins. Here’s one about reverse lights, but in others he goes through the entire harness, grounds, etc. One thing he does that you definitely do not want to do is putting dielectric grease on connections. I would follow ctmclusskey’s advice above about that stuff and the use of it, as well as the use of DeOxIt or other, similarly conductive products.
So much husband has been digging around in the car and has discovered a couple of disconnected wires under the back window inside the car. Anyone know what they could be for? Thinking it maybe for the alarm system.
Also, he's located the ground bolt and we are going to clean it and replace the nuts.
So much husband has been digging around in the car and has discovered a couple of disconnected wires under the back window inside the car. Anyone know what they could be for? Thinking it maybe for the alarm system.
Also, he's located the ground bolt and we are going to clean it and replace the nuts.
If you are talking about the ground bolt on the bsckside of the tail light housings, advise him to go cautiosly if they do not spin free easily. Those bolts snap very easily.
If you are talking about the ground bolt on the bsckside of the tail light housings, advise him to go cautiosly if they do not spin free easily. Those bolts snap very easily.
Much to our chagrin, the gremlins turned out to just be the bulbs. Apparently they all decided to go at once. Hopefully this is due to age and not something else. Oh well, the grounds got cleaned and fuse or 2 replaced. Nothing that couldn't use a little tlc 😅
Back Light Wire Gremlins
