Pontiac GTO Forum banner

1 - 18 of 18 Posts

·
Registered
Joined
·
8 Posts
Discussion Starter #1
69 4-speed car, have not found this issue anywhere. I just replaced the rear wiring harness and the tail light grounds (50 years old, was having a ground issue with left rear tail light). When I hooked the battery back up, all of the parking lights were on (front, rear, and side markers including the tail lights and back up lights). The head lights and dash lights were not on. I checked the headlight switch, it was working correctly and even replaced it...with the same results. I reviewed the wiring diagrams, I cannot find where a ground has been overlooked. Also, on the left side tail lights, I was checking for ground issues, as I turned the bulbs in their respective sockets in the tail light housing, the lights would brighten or dim, depending on which way the socket was turned. Any ideas?
 

·
Registered
Joined
·
95 Posts
Dash lights and headlights are on a separate circuit from the running lights which is why they're not affected.

Did you replace the harness just in the trunk area or from under the dash to the rear The only source of constant 12 volt power to the rear is the dome light (orange wire) circuit. Since you replaced the rear harness maybe you somehow tapped into it. Could be a mis-wire from the manufacturer or somehow the plug was inserted incorrectly.
Quick check is to pull the fuse for the Hazard/Stop lamps. If your running lights go out, that may be it.

The reason the taillights go bright and then dim is cheap Chinese bulbs. Sylvania's are the worst. The locating nubs aren't long enough to properly engage the socket guides and they can easily be installed 180* out. This would cause your brake light filament (Bright) to come on when the tail lights are on and vice-versa. I buy bulbs made in Europe or hit the junkyards for good used bulbs.

Let us know what happens.
 

·
Registered
Joined
·
53 Posts
Take all the rear bulbs out, see if the problem goes away. I had a similar problem when replacing my rear harness. Turned out to be one bulb was in backwards.
 

·
Registered
Joined
·
8 Posts
Discussion Starter #4
Correct on both replys

Each reply was absolutely correct! I installed the new harness from the fuse panel to the tail lights. I went back and double checked the plug-ins...they were plugged in correctly. Next I pulled the haz-stop fuse...lights out, so that narrowed things down. Then I pulled all of the bulbs out of the tail light sockets...problem solved! On further inspection, I had 4 bulbs from an unknown mfg made in the USA, and 2 from China. Guess which ones will not be re-installed? Thanks again for the help!!
 

·
Registered
Joined
·
8 Posts
Discussion Starter #6
Yes, replaced the fuse...just in case. I re-installed all of the bulbs in the tail lights. When I connected the battery, all of the tail lights were on, none of the parking lights. When I pulled the switch to the #2 position, all of the parking/dash lights came on and all of the tail lights turned off. Going to back track again as it still could be a bulb issue or ground. Will post again later with results.
 

·
Registered
Joined
·
8 Posts
Discussion Starter #7
From bad to worse

Ok, here is the current situation:
When you hook up the battery, the 4 tail light bulbs are on. When you pull the headlight switch to turn on the parking lights, all of the parking lights (including the plate light) come on and the 4 tail light bulbs turn off. No break lights no matter what I tried. The turn signals work. The hazards do not. I tried a couple of tests and rechecked my previous work including:

1. I tried a copper wire test (inserted a wire into the bulb socket and the other end to a ground source), each of the tail lights got brighter.
2. Next I tried a test light. It lit up on each tail light socket with the headlight switch turned off and also with the parking light in the on position. 3. There is no power getting to the back up lights no matter what the switch position is.
4. I unplugged and plugged back in all of the harness connections (at fuse box, at dome light/power, and at tail light harness).
5. I double checked all bulbs to ensure correct positions and being snug in the sockets.
6. I checked the brand new tail light ground wiring. Everything is tight. Test light worked at the bolt the wiring is fastened to.
7. Replaced the fuses.
8. Replaced the flasher unit.

One other issue, when the tail light bulbs are in the housing (all on), the driver side lights will get bright when the sockets make contact with the grounds in the housing...but only on that side. Turning the sockets on the other side has no effect on any of the bulbs.

I have reviewed the wiring diagram until my eyes have crossed. Am I looking too hard?? WHAT am I missing???
 

·
Registered
Joined
·
95 Posts
Pull the fuse for the HAZ/Brake Lts again. Test your lights using the headlight switch.
If ok, unplug turn signal switch (Long plug on top of steering column) and replace the fuse. Test
Let us know
 

·
Registered
Joined
·
3,776 Posts
1. I tried a copper wire test (inserted a wire into the bulb socket and the other end to a ground source), each of the tail lights got brighter.

PJ: Your tail light sockets will have 2 spring loaded contacts - 1 is for the brake/turn signal (the brighter of the lights), and 1 is for the tail lights. I assume you inserted the wire at some point along the side of the socket. If lights got brighter, then most likely it indicates a poor ground.

2. Next I tried a test light. It lit up on each tail light socket with the headlight switch turned off and also with the parking light in the on position.

PJ: With the headlight switch pulled out to its first "notch", your parking lights are supposed to come on. They should also remain on when you pull the headlight switch fully out.

3. There is no power getting to the back up lights no matter what the switch position is

PJ: The back-up lights do not operate off the headlight switch. Either a switch on the column/console for automatic or a switch on the transmission if manual.

4. I unplugged and plugged back in all of the harness connections (at fuse box, at dome light/power, and at tail light harness).

PJ: We have had previous instances where the fault was the dome light. I believe it was grounding out. Look at your wiring diagram and you should see how it ties into the lights.

When I connected the battery, all of the tail lights were on, none of the parking lights.

PJ: Have you checked the brake light switch under the dash which the pedal rests up against and activates the brake lights? The switch can go bad and it is adjustable. It is generally plastic and has plastic threads which can be stripped or damaged, thus moving the switch out of its position to make contact with the brake pedal and not make the brake lights come on or off.

PJ: Don't discount the front marker lights. You could have a bad ground/short in them that is bleeding over as all marker lights will be tied in together.


Your best investment at this point, rather than pull your hair out and never find the problem, is to purchase the Continuity Tester below.

I bought a Southwire brand Model 40040S Continuity Tester. I believe I bought it at Home Dept, or possibly Lowe's. It has a remote tester that can be removed from the main body and allows you to test wires/wiring from each end of the wire. It is not to be used to test for 12Volt power, just continuity. This would be perfect to test your rear harness at the plug to the tail lights. You could test from the harness plug forward, but will need to disconnect the battery as any 12Volt power source can damage the tester. Here is the PDF and you can read what it does: http://www.southwiretools.com/tools/m/file.get.do?file_id=1821
 

·
Registered
Joined
·
8 Posts
Discussion Starter #10
To: 052, I pulled the fuse. Did a test light test with the headlight switch off. No power at the tail lights. Pulled the headlight switch to the parking light position. All parking lights came on except no taillights or break lights. Test light did lite up indicating power to the socket(s) for the taillights while the switch was in that position. As for the turn signal switch, the turn signals have been working. However, they are dim at the taillights appear normal in front.

To: PJ, you may have hit on something with the dome light. My dome light has not been working for a few months (assumed it was a bulb...should have known better). I popped the cover, the bulb connectors were extremely rusty. One of the wires appeared to have sustained some heat as it was black and the wire had snapped off of the connector. Additionally, while I was under the dash, I noticed in the far left hand corner, under the vent, were three wires. One white one, two black ones. They were all tied together and hooked up to nothing. One of the black ones was connected to the door jam switch that turns the dome on when the door is open. I could not see where the other two wires go to. Going to further review the wiring diagram to see where these wires are supposed to go/connect to. Obviously, will need to re-wire the dome light. Hopefully, that will help as well (do not want to remove the headliner...its original and in good shape).

Car is a 4 speed, will get under it to see about the reverse light switch at the tranny. Brake light switch on pedal is in good shape, appears to be functioning normally. Will also re-check the front marker light grounds.

Electrical has never been my strong suit...but thanks to you guys, its improving...really appreciate the assistance. Will report back with more results
 

·
Registered
Joined
·
628 Posts
reverse light on a 69 is at the base of the steering column inside....
it is located there and the only way it works is if you have all the reverse lockout parts
working.... to spin the column collar.... like a column shift would spin ...

also ,,,, make sure the emergency flasher is not partially pushed in .... that can screw your lights up also

I have a couple other ideas but I will let Jims ideas ride till you follow up on his ideas

69's have a terrible issue with the grounds out back,,, are allyour copper grounds and the sockets where they touch clean??

also wire brush clean the copper jumper where it grounds to the tail light stud,,,,

Scott
 

·
Registered
Joined
·
8 Posts
Discussion Starter #12
Nothing changes

Just to recap, the issue at hand is when I connect the battery, the tail lights come on. When I pull the headlight switch out, all of the lights that are supposed to come do but the tail lights go out. No brake lights no matter what is done. Turn signals do work. All lights very dim.

Pulling the hazard fuse or the directional signal switch has not changed the results other than the tail lights stay off when the battery is hooked up. I have checked my diagram, all of the wires that are supposed to be at the signal switch there are. Signal switch had some dust in it but the connections were extremely clean. Neutral safety, brake light switches both appear operational.

I found three wires wired together up in the dash, under the vent on the left side. They are for the door jamb switches. It appears the drivers door has an incorrect switch as there is only one provision instead of two. I tried different measures, grounding, testing, etc. with no changes. I cleaned up the dome light wiring and lamp receivers. Cannot get them to work.

Just for the FUN of it...I climbed into the trunk, inspected the harness connections/plug ins...all good. Just to see what it would do, I disconnected the dome light power clip. When I hooked the battery back up, still no changes...the tail lights came on, no brake lights. Pulled the headlight switch, all the parking lights came on, tail lights went off, and no brake lights no matter what.

What gives....I thought the dome light was the power source for the rear harness lights?
 

·
Registered
Joined
·
95 Posts
The dome light (and other orange wires) are a source of 12 volt power with all switches and ignition off. It has nothing to do with the tail lights unless shorted or through bad grounds.
The things that have changed from before is your new harness and the discovery of the door switch grounds and the dome light wiring. If you do not have a continuity tester (ohm-meter) carefully look at the new harness plugs and insure the color codes are the same on both sides of the plug at both ends. For the dome light pigtail just above the left rear wheelhouse, make sure the orange and all other wires match on either side of the plug.
If all appear to be ok, unplug the dome light pigtail and separate the door switch wires from each other so all are not touching or connected to something. Disconnect the passenger side also. Test.
 

·
Registered
Joined
·
3,776 Posts
You have a short somewhere. First make sure your battery is at full 12Volts, not run down. Get it on a charger.

Let's recap.

1st, with battery connected, test the wire plug-in at the back of the brake light switch to see if you have 12 volts. Get an Ohm/Voltmeter to do this testing. A test light only tells you that you have power. It does not tell you what voltage you have nor if you have a lot of resistance through a bad ground. The light may go off, but you only have 6 volts or a poor ground at best.

If you have 12V at the plug-in, you should have brake lights - if not, find out why you don't have the 12volts at the plug-in.

If you do have 12Volts at the plug-in, take a piece of wire and jump the plug-in so as to make a complete circuit, just as if the switch were being pushed in and turning on the brake lights. Go back to see if brake lights are "ON". If not, start pulling all the bulbs. Then test each socket individually to see if any are getting power to them. One of the contacts in the socket is Brakes/Turn/Flasher. The other contact is for marker lights. Test the correct contact. Make sure you have a good ground on the tester. A poor ground will give you a false reading and you will think you have no power at the socket when perhaps you did.

If no power to any, then work backwards from there testing any/all plug connections until you find 12Volts. Once you do, you have isolated the problem to be from that point to the tail light sockets.

Once you have isolated the area of the problem, disconnect your battery, then use the Continuity Tester and start checking each and every wire and connection for continuity.

If the brake lights work as they should, then begin a test of all components in the marker light circuit. Pull all running light bulbs to include the front's. I might even pull the headlight plugs just to make sure they are not the problem.

Your issue could be the headlight switch or reostat control (the round spring on the switch) that dims/brightens the dash lights. Personally, I would pull that switch out and test each of the contacts/functions of the switch to eliminate it as your problem before testing all the marker light wiring seeing it controls th on/off of the marker lights. Make sure you have the ground that is needed for the switch.

You may wind up pulling the entire dash and find out that the circuit board is bad or has a short - remember dash lights come on when the marker lights come on.

The bottom line is: IF you are not willing to purchase the needed tools/testers to do the job, you are wasting your time and ours - more of yours. This could take 1 hour to find or a month when it comes to wiring issues. You may have to test a lot of wires, plugs, switches, fuse bock, grounds, and sockets to get to the root of the problem. There sometimes is no simple jump out at you "there's the problem" fix in 5 minutes. I bought a 1970 GTO Judge when younger that had a wiring issue - probably why the guy sold it, it would not charge the battery. Took several weeks to isolate the problem, testing all kinds of wiring and circuits and replaced parts. The problem turned out to be a simple broken wire inside the plastic casing which looked perfect on the outside - and was in the engine compartment. When the engine had been swapped out, it must have gotten pinched and broke.

So it may take time to find the problem, but you have to go a step at a time and note the results. Having the needed electrical testing equipment is essential. :thumbsup:
 

·
Registered
Joined
·
8 Posts
Discussion Starter #15
Have rechecked all...no changes. All wiring under the dash has been accounted for with the exception of the 3 wires associated to the door jamb switch. At this point, with the power disconnected to the dome light, I believe they are not the issue. Per the wiring diagrams, all connections match and are in their respective correct positions.

Been a long day, battery is probably down just a bit from various tests...charging it now. Will restart again later this evening or tomorrow with ohm meter/continuity testing and see where it goes.

Should have known...every small project on a 50 year old car always turns into 3 or 4 more things to do!
 

·
Registered
Joined
·
95 Posts
What Jim says. Having worked as an transit electrician (Locomotives and transit trains) for 40 years and a ships electrician for another 10, I have learned to Never say Never. Some things may seem perfectly logical when in black and white. But electricity is funny. It can be extremely frustrating at times defying all logic. And having the right tools for any profession can make your work easier in solving these illogical problems.
We'll be here to assist as well as we can.
 

·
Registered
Joined
·
8 Posts
Discussion Starter #17
Back on the road

Problem completely solved. Two issues. 1-contunity issue with a wire to a tail light socket. 2-issue with the "plunger" switch on the brake light switch (it was very "touchy" about the way it made contact when pushing the pedal in). Now I am correcting the dome light, courtesy lights, and the back up light issues (like I said...you start 1 project, end up with 3 !!!). Want to thank all (again) for your input and assistance!
 

·
Registered
Joined
·
95 Posts
Good to hear. I had a spare harness laying on the ground yesterday thinking about your problem. Thats when I saw the brake light switch in the same circuit as the dome light and wondered if that was the problem. Glad you solved it.
 
1 - 18 of 18 Posts
Top