Very weird issue with tail/sidemarker lights

Stoffauge

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Hello….it´s me :D



I wanna explain my issue the way it happenend and I hope you guys won´t be clueless like i am ;)

Car on Jackstands but complete/running.



All lights (and hazards) but brake lights work. Switched the too reverse lamps yesterday. Started the car, put it in reverse and jumped out to check the new lamps -> work fine. BUT in the same second the backlighs and all sidemarker lights went off. Headlamps (low and highbeam) still work great. Just the sidemarkers and backlights.

I have no damn clue why. Checked connections on low/high beam switch all great. Power goes to the head lights and they work but not the front sidemarker. Makes no sense to me because it´s the same wire.



Whole scenario happened twice. Somehow while checking and measuring with voltmeter it started working again. But don´t know why.



At first I was sure the headlight switch is broken but i can switch from low to high beam and back with no issues. At second I thought brake light switch but all lights worked before with the same brake light switch.



For me this is just confusing….

Hope the whole scene is understandable, if not don´t hesitate to ask. Happy about any help and hints....
 

Big_John

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Sounds like bad grounds at the lights. That's always the first thing to check when you have a light go out (or dim) when another light goes on.
 

Stoffauge

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Sounds like bad grounds at the lights. That's always the first thing to check when you have a light go out (or dim) when another light goes on.
Hey John,
I was actually hoping to get in touch with you :)

I forgot to say that the turnsignals in the back still work fine while the tail lights don´t. Should be the same ground of the housing so I think this is fine. And I don´t think the ground gets bad from one second to another like the lights actually turned off after starting the car yesterday and check the new reverse lamps...

I was hoping you say: brake light switch or beam selector right away! (easy to replace)
 

Stoffauge

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Like Big_John said, a bad/weak ground will cause the issues you describe.

It´s not that I wouldn´t trust in you guys knowledge and experience. it just doesn´t make sense to me that the turn signals work (same bulb, same ground on housing of taillights) but not the tail lights itself. And that the tail lights turn off from one to antoher second without dimming or glowing in between if ground is bad. And in additon the front sidemarkers don´t work either in combination with the tail lights.

And everything worked fine before i started the car to check reverse lights.

WIll check tail light housing ground but still not sure if it´s really the cause....

Thanks anyways
 
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SPF Required

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I recently had some funkiness going on at the rear lights on my ‘68 300. I followed the advise of others here and started by checking grounds at the rear, then started moving up the harness towards the dash. The group here made me aware of the many connections concealed behind the driver side kick panel. The culprit in my case was to connector at the base of the steering column to the turn signal switch. The terminals in that connector (it’s like a 10-pin connect) we’re a bit oxidized and a few were even a bit loose. Cleaned and tightened things up there and so far the rear light issues have not repeated themselves.

but like the guys said above, start at the grounds in the back and work up from there.


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65sporty

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If you start with the grounds and find all is good, you will want to check power. I don't have a wiring diagram in front of me and not sure what your working on either, but I would start at the headlight switch to check power.
 

Stoffauge

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Hey guys.....a bad beam selector switch caused the problems. All solved, thanks :)

Now just the brake lights don´t work. But I am pretty sure it´s the turn signal switch. Brake light switch sends 12v perfectly while pushing the pedal to the tss but the tss doesnt sends the 12v in the back via the dark green cable.
So I think I need a new one. Guess still the original one and got old.

May I be right ?
 

SPF Required

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Glad to here things are headed in the right direction. There are a couple/few connectors between the tss and the rear light harness. I had fully committed to replacing my tss, even bought the tss (which is not an insignificant purchase for a tilt/telescoping column), but then followed the advice of the c-body sages on this forum to check voltage at every connector first. One in the trunk, one at the driver kick panel, and one at the base of the column.

Tested each bulb first with a 12 volt power source. They all worked.

Had my 11 year old squash the brake pedal when asked (easy task for him while playing on his switch) and used a test light. That’s when I discovered the problem at the connector at the base of the column. Saved me from having to tear down my column (for now at least).
 

Stoffauge

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Hey guys,

after working up all grounds af the lights and sidemarkers I think I know whats causing the issue with the sidemarkers/taillights (all other lights work). THe headlight switch . It gets full power but doesnt connect internally when switching on. I jumped/bypassed it and all worked fine. I really hope I can rebuild/open it up and don´t have to find a spare one.

Thanks for all your hints and help as always
 
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