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Old 09-09-2017, 10:17 PM   #1
chad64chevy
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brake light and turn signal help, PLEASE!!

I have a 1966 swb fleetside truck

ok, so I have left turn signal front and back only also headlights work! no brake lights at all on either side or right turn signal or tag light! I have replaced dimmer switch and pigtail, head light switch, front turn signal harness in hood, brake light switch, turn signal switch in column! I have added grounds to the front turn signal housings

I have my battery grounded to the motor and my ground straps are; motor to frame, frame to cab, bed to frame, both inner fenders grounded to frame! I have also checked with another turn signal switch just plugged into the harness, same thing happens!

I think its a ground problem cause with the headlights on the driver side is brighter then the passenger side, when I use the right turn signal the gauge cluster light just stays on but when checking the lights then are not on or blinking! i'm confessed with what it can be

should I just ground the battery to the frame instead of the motor?? I did this when I put in the sbc and th400 a few weeks ago!

any help would be great!!
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Old 09-10-2017, 01:02 PM   #2
chad64chevy
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Re: brake light and turn signal help, PLEASE!!

so update my gauge cluster right turn signal flashes but nothing at the front or rear lights!

starting to think it could be the main harness?? any thought, anyone!!
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Old 09-10-2017, 01:45 PM   #3
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Re: brake light and turn signal help, PLEASE!!

Lets brake this down a little.

Quote:
Originally Posted by chad64chevy View Post
I have a 1966 swb fleetside truck

ok, so I have left turn signal front and back only, also headlights work! no brake lights at all on either side, or right turn signal or tag light! I have replaced dimmer switch and pigtail, head light switch, front turn signal harness in hood, brake light switch, turn signal switch in column! I have added grounds to the front turn signal housings

The signal light wires are the same wires as the brake lights. If your left signal rear works it means that you have ground on the left and power on the left signal but no power on the left brake.
The wire from the brake switch lights both the left and right lights via the turn signal switch. This means that you have no power or no ground on the right turn/brake wire. Since neither side brakes works you probably have no power going to the turn signal switch (white from brake switch}.

The orange wire in the fuse panel sends power to the headlight switch for the parking lights and the tag light. it also sends power to the brake light switch. you need to check it for power at the fuse panel, and at the stop and headlight switches.


Here is a diagram of the wires and if you look at the bottom center you will see the fuse panel. Locate the orange wire and follow it up to the left side to the brake switch and in the center to the headlight switch.
The dashed line (white wire) from the brake switch goes up to the turn signal switch to feed the left and right brake light wires.

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I have my battery grounded to the motor and my ground straps are; motor to frame, frame to cab, bed to frame, both inner fenders grounded to frame! I have also checked with another turn signal switch just plugged into the harness, same thing happens!

I think its a ground problem cause with the headlights on the driver side is brighter then the passenger side,This is a local problem withthe left headlight not being grounded well,when I use the right turn signal the gauge cluster light just stays on It will because there is not evough current going through the flasher to cause it to blink but when checking the lights then are not on or blinking! This could be a grounding problem on the right side. i'm confessed with what it can be.

should I just ground the battery to the frame instead of the motor?? I did this when I put in the sbc and th400 a few weeks ago!

No you always want to ground the battery to the motor first because the starter is the biggest draw in the truck and it needs the most ground.
Your ground method sounds OK but you may have grounding problems on the lights themselves.

any help would be great!!
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Old 09-10-2017, 10:16 PM   #4
chad64chevy
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Re: brake light and turn signal help, PLEASE!!

thanks vettevet,

so trying to solve this problem didn't help today! I replaced the dome light harness and housing cause it wasn't working either an it was old an broke, also no power to the orange wire at all! so the plan is, I ordered a new oem main harness from classic parts today! another reason for me ordering a new harness is I noticed it blew the stop light fuse an as I was changing it out, battery still connected it was arching really bad!making me think that the main harness was grounding itself out or not grounding and no thing I could think of was helping so I disconnected the battery a will wait til the new harness shows up!

also I have a hd headlight relay harness from lmc that I would like to install but it has a three wire prong coming out of it an not a two prong connection like the original harness does, it has a solid blue an solid yellow wire going to both lights an each have a ground wire, there's two relays! both yellow wires go to one an both blue wires go to another for the low an high beams, both relays have red wires going to battery, then a brown wire comes off one and a white wire comes off the other a blue wire with a white stripe goes to both of them! the brown, white and blue w/ white stripe go to the three prong! how would I wire this to work for me??

looking up how to wire in a headlight relay harness, my thinking is the blue wire with white stripe is a ground, the brown wire can go to the brown wire under the hood and the white wire can go to green under the hood! am I right or am I wrong, thanks for your help !!

Last edited by chad64chevy; 09-10-2017 at 10:23 PM.
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Old 09-11-2017, 12:10 PM   #5
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Re: brake light and turn signal help, PLEASE!!

.........................
Quote:
Originally Posted by chad64chevy View Post

so trying to solve this problem didn't help today! I replaced the dome light harness and housing cause it wasn't working either an it was old an broke, also no power to the orange wire at all! so the plan is, I ordered a new oem main harness from classic parts today! another reason for me ordering a new harness is I noticed it blew the stop light fuse an as I was changing it out, battery still connected it was arching really bad!making me think that the main harness was grounding itself out or not grounding and no thing I could think of was helping so I disconnected the battery a will wait til the new harness shows up!

Most likely you shorted the orange and white wire going to the dome light while you were changing out the harness with the battery still connected. The orange wire is hot all the time as long as the battery is connected and the white wire is the ground side and you probably had the door open while you were working on the harness. This connects the white wire to ground and the orange wire is hot so Poof there goes the fuse.

also I have a hd headlight relay harness from lmc that I would like to install but it has a three wire prong coming out of it an not a two prong connection like the original harness does, it has a solid blue an solid yellow wire going to both lights an each have a ground wire, there's two relays! both yellow wires go to one an both blue wires go to another for the low an high beams, both relays have red wires going to battery, then a brown wire comes off one and a white wire comes off the other a blue wire with a white stripe goes to both of them! the brown, white and blue w/ white stripe go to the three prong! how would I wire this to work for me??

Doesn't your headlights have a three wire plug? The GMC trucks have 2 bright bulbs with two wire plugs and the other 2 have 3 wire plugs I think, but chevys all have just 2 bulbs with 3 wire plugs as far as I know.

You will have two wires in the truck harness that will power the relays in the HD harness. A green one for brights and a tan one for dims. These two wires will come from the dimmer switch and go to the no. 86 on each relay. Then we will have to figure out which wires will ground the relay to no.85 on the relays. Lets wait until you get the new harness installed to get into this phase.


looking up how to wire in a headlight relay harness, my thinking is the blue wire with white stripe is a ground, the brown wire can go to the brown wire under the hood and the white wire can go to green under the hood! am I right or am I wrong, thanks for your help !!
Let's wait until the new harness is in.

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Old 09-11-2017, 06:16 PM   #6
chad64chevy
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Re: brake light and turn signal help, PLEASE!!

anytime I worked on the wiring the truck was disconnected, my truck is a 1966 c10 with two 7" round lights the back of the lights have three prongs per light, but the headlight harness relay kit where it plugs into my original harness in the radiator support has two wires a tan wire and a green wire! but in the headlight harness relay kit there is a three prong like in a 67-72 chevy truck
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Old 09-11-2017, 11:11 PM   #7
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Re: brake light and turn signal help, PLEASE!!

Quote:
Originally Posted by chad64chevy View Post
anytime I worked on the wiring the truck was disconnected, my truck is a 1966 c10 with two 7" round lights the back of the lights have three prongs per light, but the headlight harness relay kit where it plugs into my original harness in the radiator support has two wires a tan wire and a green wire! but in the headlight harness relay kit there is a three prong like in a 67-72 chevy truck
These retail headlight relay kits are designed to be plug and play with no wiring.
What they have us do is unplug the headlight plug and plug the relay wires into it and then plug the relay plugs into the headlights.

Let me explain.

The power for your headlights comes from the dimmer switch and runs in the harness to the engine compartment to the left headlight via two wires. A light green wire for the bright lights and a tan wire for the dim lights.
Both of these wires are in the left headlight plug along with two other wires that jump over to the right side headlight plug to give it bright and dim power.
There is also a ground wire in the left headlight plug that grounds to the radiator support.

Here's the diagram with the left headlight plug in the lower left of the diagram.

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The two headlight wires are coming to the baffle connector in the bottom left of the diagram and then up to the left headlight and up to the right headlight.

The left headlight plug should plug into the two wire plug in the relay harness and the two three wire plugs should go to the left and right headlights.

You will have to figure out where the wire comes from that feeds the two relays with 12 volts and then the relay closes and feeds the two headlight plugs.

I would have ordered a new harness with the HEI ignition conversion and the internally regulated alternator conversion made into it if you could have gotten it.
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Old 09-15-2017, 09:21 PM   #8
chad64chevy
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Re: brake light and turn signal help, PLEASE!!

ok VetteVet,
got the new main harness that goes under the dash! still not working right, I'll explain!

first I can press the brake pedal and only get a dim driver side tail light!

I can put the key in an turn to aux. an get driver side turn signal front and back no problem, when I turn the passenger side turn signal I get the front one only and it's dim, no light in the back! when I turn on the headlights, I get lights in the back and tag light but when I press the brake driver side rear light goes off and passenger side goes dim

dome light works no problem, gauges lights up no problem! to ground the rear tail light housing, how would I do that on a fleetside bed?

all the wiring in new from classic parts, not sure if its a ground or what
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Old 09-15-2017, 09:25 PM   #9
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Re: brake light and turn signal help, PLEASE!!

on the brake lights why would one go dim and one go out, but when I let off the brake the lights go back on
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Old 09-16-2017, 09:22 AM   #10
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Re: brake light and turn signal help, PLEASE!!

These are classic bad ground symptoms. You should start at the engine block and run a ground over to the frame then from the frame to the box in the rear.
The mounting screw on the tail light should provide the ground for the tailight housing if it's clean and tight and the box to frame ground is clean as well.

Electricity is just like water in plumbing. It will follow the path of least resistance and the resistance is poor grounds. The more lights you turn on the less power you have for each of them, so they will get dim or bright based on the poor grounds on each light.

when you turn the key to auxiliary you get more voltage to overcome the bad grounds and the lights work better. It sounds like the main culprit is the frame to bed ground and the frame to battery negative ground.
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Old 09-16-2017, 09:46 PM   #11
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Re: brake light and turn signal help, PLEASE!!

ok, so I have ran ground wires to each rear tail light housing, which helped when I applied the brake both rear brake lights worked! but I figured that the lights should be dim and when I press the brake that's when they should go bright! but they don't there bright and then go dim when I apply the brake! also when I applied the brake with the driver side turn signal on and the left rear goes out and it stops blinking on the gauge cluster and front and back! when I turn the right turn signal on both rear light blink and are dim! going to replace headlight switch and turn signal switch! I ran 12guage grounds to the rear light housings to the frame and ran 10gauge grounds from the cab to frame both sides, and 12gauge grounds from bed to frame both sides front and back (4), then ran a 4gauge ground from engine to frame! not sure if it's over kill but it can't hurt right!!

also side note, I ordered the front harness that has internal regulator alternator on passenger side, it's the only harness that isn't new, I have a proform ready to run dizzy in it and it's wired right, I didn't get the hei engine harness
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Old 09-17-2017, 09:45 AM   #12
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Re: brake light and turn signal help, PLEASE!!

Your post just screams at me that you have the brake light bulbs in backwards. That isn't possible though because the bulbs have small lugs on them that fit in the sockets only one way. Have you checked the numbers to make sure they are the correct bulbs for the sockets in the tail lights? 1157 I believe is the correct number, or have you forgotten to tell us that you have LEDs installed. I have been trying to think of somewhere in the harness that your brake light wire and the tail light wire are crossed and the best place is in the harness connector on the firewall behind the distributor.

The problem with that, is that there is only one brown tail light wire and there are two brake light wires. So how do we get one tail light wire to power two brake light wires.

It could be done at the tail light sockets if both brown wires were crossed in each socket. I would think that it would be obvious to spot that, but it could be missed.

When you step on the brake does your license plate light up, or any other lights besides the two dim brake lights?

The tail lights do not go through the turn signal switch so you could unplug it at the column connector and step on the brakes and see if the tail lights come on.
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Old 09-17-2017, 07:11 PM   #13
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Re: brake light and turn signal help, PLEASE!!

Quote:
Originally Posted by chad64chevy View Post
on the brake lights why would one go dim and one go out, but when I let off the brake the lights go back on
Classic symptom of a bad ground, the increased load of the stop lights makes the ground circuit "go away".
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Old 09-18-2017, 12:14 PM   #14
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Re: brake light and turn signal help, PLEASE!!

so I got the problem fixed I started at the firewall and worked my way back to the tail lights to look for anything wrong on the harness and found the green wire to be punched and grounding to the frame! once that was fixed everything worked like it should! left and right turn signals worked, brakes got brighter as I pushed on the brake pedal, right turn signal flashes a lil faster then I think it sould but, they all work great now! also got the headlight relay harness wired in an working that makes a huge difference!

as far as led bulbs go I do have a them but haven't installed them is there anything I should do to get them to work right, now that I got this problem fixed?

thanks guys, for being patient with me
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