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Old 03-21-2011, 07:45 PM
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Taillights don't work with headlights on??

Been working on this for a week and it is driving me nuts. Trying to wire my lights back up on my 66 truck. So far everything works, front blinkers, rear blinkers , turn signals and stop lights until I turn my headlights on then the blinkers don't work and my rear lights are at full light strength like the brake pedal is pushed in. If I disconnect my main wire (brown) for hot and hook it directly to the left turn light then it is over powered and the right turn light works and vice versa. All my fuses are good and I checked grounds on headlights and rear lights. So in short I am good until I have to turn my headlights on then brake nor turn signals work and during this time my rear lights are at full brightness. Any help is appreciated. Thx in advance.

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Old 03-21-2011, 08:13 PM
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badriand,

I think you may have the wrong elements lighting up.
There are two elements within one bulb. tail lights and frount running lights will be connected to the headlights. The turn signals and brake lights run through the turn signal switch. So when you turn the switch to the left the brake voltage will be disconnected and the flasher will be connected so that both front and rear turn elements light up. The turn signal switch, when in neutral the brake lights light but not the front turn signal element. So check that you if have hooked up the turn/brake elements to the headlights.

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Old 03-21-2011, 08:52 PM
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Sorry for my ignorance but are you talking about under the dash? I am still using the original wiring and nothing looks like it crosses or is tapped into the headlight switch that would cause it. The harness that runs to the back is separate from the head lights. Maybe i am looking it wrong.
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Old 03-21-2011, 09:02 PM
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First of all, you have got to tell us what you are working on. In 1966 it could be a Ford, Chevy, International, Dodge, or a Datsun.
Headlight are a separate circuit. The light switch combines several switches into one control. The headlights may have a fuse, or more commonly on domestic vehicles, there is a circuit breaker in the light switch, for the headlight section only.
The taillights have their own part of the light switch. The power for the taillignts is probably fused. The taillight power probably also goes to side marker lights, if your truck has them,
The light switch may also have a dimmer for the dashboard lights.

The headlights should not affect the operation of the turn signals. If they do, it is wired wrong, or you have bad grounds.
If your truck does not have separate turn signals, and brake lights,on the rear of the vehicle, The brake light power goes through the turn signal switch.

This is what I would do. I would remove the taillight fuse, and turn on the headlights. Only the headlights should come on, except for the high beam indicator in the dashboard, if you are on high beam. No other lights should come on, not even glow a little bit.

Put the taillight fuse back in. Turn on the taillights. Make sure only the taillight element in the taillight bulb is on, for all the taillights. Get them all working.

Now for the turn signals, and brake lights, and if you have them, the emergency flashers.

If you have emergency flashers, get them working next. This will let you know the wiring and the lamps (bulbs) are all good for the turn signals, and if they are combined, the brake lights.

Once the emergency flashers work, make sure the brake lights work. Remember the brake light power goes through the turn signal control, so when you signal a turn, the turn signal can cancel the brake light on one side.
Now, finally you can work on the turn signals.
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Old 03-21-2011, 09:20 PM
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Sorry, it is a 66 chevy c10. I don't have emergency flashers. The wiring is just brown/green/yellow/light green to the rear lights and yes the brake light works off the turn signal light. I will try your suggestions. Thx.
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Old 03-22-2011, 05:39 PM
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OK still have issue. I still have original harness and from what I can tell is headlight and taillights feed into the same part of the harness. I have both a yellow wire and a red wire coming from the blinkers and headlight switch that tie together. If i take a tester light to both the red and yellow both give a blink on the tester with blinkers on. The yellow is a bright light and the red is a lower light. I cut the yellow one for testing but seems that one feeds the power to the rear signals.
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Old 03-22-2011, 05:49 PM
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I am a little confused with this, so I will just do the basics since that is always the best place to start. First of all and very important, is that each light has a proper ground. On this old truck that would be a good place to start. Once you have established a ground, turn on the parklights and check for power at the rear lights. There should be power at each taillight and verify that it is the dimmer of the two elements burning. Try both wires at the bulb socket to confirm. Then hook the turn signal wires to the other wires at the bulb sockets. Just to repeat. None of it will work right without a GOOD ground....Allan

GM steering column connections
White stop light switch
dark green right rear stop light and turn signal
yellow left rear stop light and turn signal
purple turn signal flasher
brown hazard flasher
dark blue right front turn signal
light blue left front turn signal
black horn

BTW, Just ignore the coding that doesn't apply to your application
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Old 03-24-2011, 01:37 PM
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The yellow wire coming from the TS switch goes to the left rear turn/brake lamp (bright filament). No other wire should be connected to the yellow wire.
If the yellow wire is powered by the headlight switch it will backfeed through the TS switch and feed the orange wire and light up the both rear turn/brake lamps.
The red wire is the 12 volt feed to the headlight switch.
This red wire is hot at all times. My guess is that the headlight switch is incorrectly wired.


vicrod
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Old 03-24-2011, 01:58 PM
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In Chevy trucks it was almost always the brown wire for the parking lights in the rear.
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Old 03-24-2011, 02:55 PM
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Quote:
Originally Posted by T-bucket23
In Chevy trucks it was almost always the brown wire for the parking lights in the rear.
X2 . What I posted is the wiring coming down the steering column. Glad that you clarified that the brown wire in the rear harness is for the taillights . Interesting side note that every trailer wiring harness that I have seen is color coded the same as Chevy. Allan
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