Need help ASAP with tail-light wiring
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Mountain Pass
Joined: Jan 2006
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Need help ASAP with tail-light wiring
Sorry for the urgency but I am leaving Monday on a hunting trip. I know this info is here somewhere but I can;t find my answer.
I installed the wooden bed and started hooking up new lights. I cut the wiring harness a foot beyond the plug at the back bumper. I have the two brown wires, the two black/red wires, the green, and the yellow.
I have brake lights but no running lights. I am not getting 12V at the harness plug (unplugged) when the lights are on. Fuses are good because I have running lights at the front of the truck.
Any guidance would be greatly appreciated!
I installed the wooden bed and started hooking up new lights. I cut the wiring harness a foot beyond the plug at the back bumper. I have the two brown wires, the two black/red wires, the green, and the yellow.
I have brake lights but no running lights. I am not getting 12V at the harness plug (unplugged) when the lights are on. Fuses are good because I have running lights at the front of the truck.
Any guidance would be greatly appreciated!
Knuckle Bandage Sales Rep
Joined: Feb 2011
Posts: 3,673
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From: Maine
Stone, the brake lights are fed from a different point than the tail lights and turn signals. Something is happening downstream from your headlight switch is my guess since you have front lights working.
Do you have a solid ground going to the tail light housings that is directly connected to the frame and not to your isolated wooden bed? Wait, scratch that - then your brake lights wouldn't be working. Perhaps the wires for running lights got crimped somehow during the bed replacement process. Might want to run a dedicated temporary line to the rear from the front lights or light switch just so you can go on the hunting trip. Then sort it out better later. Do your turn signals work? If not then that is helpful to know where the line break may be happening. Snoop around near the steering column harness to see if there is any wire damage.
Tom
Do you have a solid ground going to the tail light housings that is directly connected to the frame and not to your isolated wooden bed? Wait, scratch that - then your brake lights wouldn't be working. Perhaps the wires for running lights got crimped somehow during the bed replacement process. Might want to run a dedicated temporary line to the rear from the front lights or light switch just so you can go on the hunting trip. Then sort it out better later. Do your turn signals work? If not then that is helpful to know where the line break may be happening. Snoop around near the steering column harness to see if there is any wire damage.
Tom
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Mountain Pass
Joined: Jan 2006
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Thanks Tom! I will run a dedicated wire if I can't find it today.
Here are the circumstances thus far.
Here are the circumstances thus far.
- I had running lights right before I cut the harness and unplugged the harness at the back so it could be something in the harness itself.
- I am using waterproof trailer lights since they will be outside the body and exposed to the elements.....no frame ground.
- I have verified that the two brown wires have continuity to the frame.
- So far, I have only verified that I have brake lights but I will try turn signals today and all else fails, I will run the dedicated wire.
Logistics Pro
Joined: Jul 2005
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Do you have gauge lights? I believe they're on the same fuse circuit as the tails.
Check the wiring near the connectors you unplugged. You can do this by hooking up a continuity tester or a test-light, and wiggling each individual wire by itself, at/near where it goes into the connector.
And check any wiring you've done.
I converted my '88 Mustang GT to mass air, in maybe three hours one night, but it wasn't running right, and I don't think it was giving me any error codes or lighting the Check Engine Light. I went back the next night and double-checked my wiring, and found that I'd accidentally swapped two of the wires to the mass air sensor! Fortunately it didn't mess up the computer, and it ran mint once I swapped the two wires where they needed to be.
Being the tail/running lights, they don't need to flash or do anything besides being manually turned on and off. Bearing that in mind, if all else fails, you can just get a bunch of wire, and make your own temporary tail light circuit, controlled by a toggle switch from in the cab - or you can even just twist the wires together if you're switching the ground side, and not the positive side...
Check the wiring near the connectors you unplugged. You can do this by hooking up a continuity tester or a test-light, and wiggling each individual wire by itself, at/near where it goes into the connector.
And check any wiring you've done.
I converted my '88 Mustang GT to mass air, in maybe three hours one night, but it wasn't running right, and I don't think it was giving me any error codes or lighting the Check Engine Light. I went back the next night and double-checked my wiring, and found that I'd accidentally swapped two of the wires to the mass air sensor! Fortunately it didn't mess up the computer, and it ran mint once I swapped the two wires where they needed to be.
Being the tail/running lights, they don't need to flash or do anything besides being manually turned on and off. Bearing that in mind, if all else fails, you can just get a bunch of wire, and make your own temporary tail light circuit, controlled by a toggle switch from in the cab - or you can even just twist the wires together if you're switching the ground side, and not the positive side...
Logistics Pro
Joined: Jul 2005
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Someone please answer this.
Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
Keep in mind when - you say something has "continuity", that doesn't mean it will necessarily carry enough current to actually light a bulb. Maybe that's what you meant, but for example those "beep" signals on a DVOM can be deceptive. A single strand of 14 gauge will show "continuity", after all.
Logistics Pro
Joined: Oct 2006
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From: East Central Ia
I thought the plug at end of frame only had 4 wires? Left turn/brake Right turn/brake running lamps and reverse lamps. On my 78 the grounds for tail lamps and side markers are behind the tail lamps are on a screw into the box on both sides, Tail lamps should be on fuse. Check under hood at firewall connector to rear.
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Moderator & parts slinger
Joined: Feb 2007
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From: S/W Missouri, Polk county
Here's what the factory wiring diagram says for rear lights.
Blk/rd= backup lights
Black= side marker, tag lights (on styleside)
Brown=tail lights, tag light (on flareside)
green= RH stop and brake
Yellow/blk= LH stop and brake
Rear light wiring:
BROWN: running light circuit
YELLOW with BLACK stripe: driver-side stop/turn
GREEN: passenger-side stop/turn
BLACK with RED stripe: backup lamps
73 & 79 headlight-marker lights use same color codes
Brown= side marker and parking lights
White-blue trace= turn signal
Red-black trace= Low beams
Green-black trace= Hi beams
Black=ground
Flat bed wiring…
Brown= Run Light
Green= Brake light- L
Yellow= Brake Light- R
Black= Reverse Light??
Blk/rd= backup lights
Black= side marker, tag lights (on styleside)
Brown=tail lights, tag light (on flareside)
green= RH stop and brake
Yellow/blk= LH stop and brake
Rear light wiring:
BROWN: running light circuit
YELLOW with BLACK stripe: driver-side stop/turn
GREEN: passenger-side stop/turn
BLACK with RED stripe: backup lamps
73 & 79 headlight-marker lights use same color codes
Brown= side marker and parking lights
White-blue trace= turn signal
Red-black trace= Low beams
Green-black trace= Hi beams
Black=ground
Flat bed wiring…
Brown= Run Light
Green= Brake light- L
Yellow= Brake Light- R
Black= Reverse Light??
Lead Driver
Joined: Jul 2017
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From: San Jose, CA
As you can see from what the others have said, the Brown wires are NOT ground wires. They're the 12v signal to the running lights.
The brake lights and turn signals are THE SAME WIRES as far as the lights are concerned. The change-up happens in the turn signal switch. From there back though, the wires for STOP and TURN are the same. And therefore the bulb filaments are the same too, as you probably already knew.
If there is not a separate ground wire with the new lamp housings, you will have to add them yourself.
Paul
The brake lights and turn signals are THE SAME WIRES as far as the lights are concerned. The change-up happens in the turn signal switch. From there back though, the wires for STOP and TURN are the same. And therefore the bulb filaments are the same too, as you probably already knew.
If there is not a separate ground wire with the new lamp housings, you will have to add them yourself.
Paul
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Mountain Pass
Joined: Jan 2006
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Okay, 90% of the way there! Everything is working except the turn signals and I am sure that is being caused by the flashers since I put LED lights in, they aren't drawing enough current to trip the flasher. I just have to find the right electronic flasher.
If anyone has experience with this I would greatly appreciate help as I have no clue how to find the right flasher.
If anyone has experience with this I would greatly appreciate help as I have no clue how to find the right flasher.
Thread Starter
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Mountain Pass
Joined: Jan 2006
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I got an electronic flasher and that didn't work, I suspect because I have a combination of incandescent bulbs (front) and LED bulbs (rear). Got another regular flasher with lower rating and it's all working.
Now I am tinkering before I leave tomorrow and I have no voltage at the dome light. No idea how to find that wire. All the fuses are good.
Now I am tinkering before I leave tomorrow and I have no voltage at the dome light. No idea how to find that wire. All the fuses are good.
Logistics Pro
Joined: Jul 2005
Posts: 4,217
Likes: 154
I got an electronic flasher and that didn't work, I suspect because I have a combination of incandescent bulbs (front) and LED bulbs (rear). Got another regular flasher with lower rating and it's all working.
Now I am tinkering before I leave tomorrow and I have no voltage at the dome light. No idea how to find that wire. All the fuses are good.
Now I am tinkering before I leave tomorrow and I have no voltage at the dome light. No idea how to find that wire. All the fuses are good.
Keep in mind when - you say something has "continuity", that doesn't mean it will necessarily carry enough current to actually light a bulb. Maybe that's what you meant, but for example those "beep" signals on a DVOM can be deceptive. A single strand of 14 gauge will show "continuity", after all.
However, if you go back and re-read my above post, you'll see how rudimentary my electrical skillz are: I was recommending that the continuity test function (or in a pinch, a test light) be used to facilitate a wiggle test, on the suspect wires.
My typical test light is a 194 bulb and some speaker wire, so I'm sure you can see where I'm coming from...
Moderator & parts slinger
Joined: Feb 2007
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From: S/W Missouri, Polk county
For the domelightwire, hot-at-all-times power comes goes to the headlight switch as a GREEN with YELLOW stripe wire. Domelightpower comes back out as a BLACK with BLUE stripe wire. The same color scheme is used at the door jamb switches. BLACK with BLUE stripe runs out to the actual domelight. BLUE with a RED stripe is instrument panel illumination. It comes out of the headlight switch to the fuse box, leaves the fuse box again as the same color and is distributed throughout the dash.
There is no ground connection to the domelightswitches or the headlight switches. These switches switch power, not ground.
1) Make sure you have 12 volts on both sides of the courtesy lamp fuse. This circuit is hot at all times, so it doesn't make a difference what position the key is in. If you have power on only one side, replace the fuse. If you don't have power on either side, then there is other work to do first.
2) Pull the domelightswitches out and remove them. Make sure the terminal for the GREEN with YELLOW stripe wire in the connector has power.
3) Check the domelightswitches for continuity. With the plunger all the way out (switch CLOSED), the switch should be shorted. With the plunger pushed all the way in (switch OPEN), the switch should be open. If not, replace the switch.
4) With power to the switch proven to be good, and the switches proven to be good, the domelightshould lightup. If the domelightdoes not lightup, remove the cover and check for power at the domelight(not the side that's permanently grounded to sheetmetal) with the door OPEN. If you have power here, yet the bulb does not lightup, replace the bulb.
This will prove out the door-side; if you get to the point that the doors turn the lighton but the headlight switch will not, then we can cross that bridge.
There is no ground connection to the domelightswitches or the headlight switches. These switches switch power, not ground.
1) Make sure you have 12 volts on both sides of the courtesy lamp fuse. This circuit is hot at all times, so it doesn't make a difference what position the key is in. If you have power on only one side, replace the fuse. If you don't have power on either side, then there is other work to do first.
2) Pull the domelightswitches out and remove them. Make sure the terminal for the GREEN with YELLOW stripe wire in the connector has power.
3) Check the domelightswitches for continuity. With the plunger all the way out (switch CLOSED), the switch should be shorted. With the plunger pushed all the way in (switch OPEN), the switch should be open. If not, replace the switch.
4) With power to the switch proven to be good, and the switches proven to be good, the domelightshould lightup. If the domelightdoes not lightup, remove the cover and check for power at the domelight(not the side that's permanently grounded to sheetmetal) with the door OPEN. If you have power here, yet the bulb does not lightup, replace the bulb.
This will prove out the door-side; if you get to the point that the doors turn the lighton but the headlight switch will not, then we can cross that bridge.