I hate wiring

[chevymanjt]

Hey guys, working on the 68 trying to get it back on the road and I’ve ran into a problem. I have headlights and hazards, but no tail, brake, or reverse lights. I unplugged the rear harness from inside the cab and ran a jumper to the rear harness and they worked. I also checked for 12v on the orange wire on the backside of the fuse box and there is none. I’m an idiot when it comes to electrical so I have no idea what this means, any help is greatly appreciated!

[hooverfish]

Try attaching one end of a ground wire to bed sheet metal and other end to the frame, worked for me.

[chevymanjt]

Originally Posted by hooverfish

Try attaching one end of a ground wire to bed sheet metal and other end to the frame, worked for me.

I’ve added about three extra ground straps throughout and just to make sure it wasn’t that, I ran a ground straight from the battery to the tail lights. My brain is exhausted from this

[chevymanjt]

So if I’m understanding this correctly, if I have no power at the orange wire on the back of the fuse box, does that mean the orange wire contact on the back side of the box is dead?

[dmjlambert]

Most likely means the TAIL STOP fuse is bad, or the contacts holding the fuse are corroded. I suggest use a test probe or multimeter to check for voltage on both sides of the fuse.



If you ran jumpers and it worked, it sounds like you're making progress.

[chevymanjt]

Originally Posted by dmjlambert

Most likely means the TAIL STOP fuse is bad, or the contacts holding the fuse are corroded. I suggest use a test probe or multimeter to check for voltage on both sides of the fuse.



If you ran jumpers and it worked, it sounds like you're making progress.

I used a multimeter on it and have 12v on one side of the fuse, but not the other. The fuse is new

[dmjlambert]

Where were the multimeter probes touched, on the metal ends of the fuse itself or on the clip that holds the fuse on each end? If on the metal ends of the fuse itself, that means it is a bad fuse. If on the clip that holds the fuse, probably corrosion on the clip.

[chevymanjt]

Originally Posted by dmjlambert

Where were the multimeter probes touched, on the metal ends of the fuse itself or on the clip that holds the fuse on each end? If on the metal ends of the fuse itself, that means it is a bad fuse. If on the clip that holds the fuse, probably corrosion on the clip.

I did both, but as it turns out that “new” fuse want any good. So now I have tail lights but still no brake lights

[dmjlambert]

If the fuse looks good but tests bad, that is probably a manufacturing defect. If it is blown, it could have been instantly blown when you touched the brake pedal the first time after installing the fuse, because you have a short somewhere.

[HO455]

It is not uncommon for the back of the fuse block to get corroded and lose conductivity. The metal tabs that hold the fuses in place are riveted to the bus work (or individual wires) and those rivets are what make the connection tight. When corrosion gets in between the rivet and the metal parts conductivity is lost or voltage drops too low to operate a small load like a taillight.
By checking to each individual metal piece of the fuse holder you can locate where the voltage is lost. Basically you will need to start at the last known location of voltage and test every single connection. Now an easier way to do this is to put your meter leads on each side of the connection and check for DC voltage. If you find ZERO volts the connection is good. Like putting your positive meter lead on the battery positive post and the negative meter lead on the positive battery cable clamp. A good solid connection will drop no voltage so no voltage can be detected with your meter.

Now if your meter reads some voltage then there is a problem. The higher the voltage you detect the higher the resistance of the connection and the more voltage is lost. For example If you have a connection like the one the red arrow points to (Photo below) and one lead is on the rivet and one lead is on the silver bus piece next to it and your meter indicates 3.2 volts. That means the voltage will drop 3.2 volts there. So If your battery voltage was 12.5 volts all the circuitry after that point would only be 9.3 volts. If one other connection drops 3.5 voltage it will keep your lights from lighting. This problem of voltage loss is not limited to the positive side of the wiring. Every poor ground connection contributes to the voltage dropping. How many ground connections are between the negative battery post and a taillight bulb? 2? 3? 5?

These connections could also have been damaged by an overheated circuit in the past like some of the ones shown below.

I harvested this photo from a post VetteVet posted (Thank you sir) and added the arrows to help show problem areas.

Green arrow rusty connection possible voltage drop where wire is crimped into the metal tab.

Red arrow overheated connection. Notice blackened rivet it has been very hot in the past. Expanding with the heat it deformed and now may be loose. In addition the heat burnt off any anti corrosion coating and it is vulnerable to corrosion.

Blue arrow damaged wire that has been repaired. Properly? You wouldn't know until you took it apart.

Here is the thread where I got the photo from. And once again thanks to our wonderful newly promoted moderator VetteVet!

http://67-72chevytrucks.com/vboard/s...968+fuse+block

[chevymanjt]

Originally Posted by HO455

It is not uncommon for the back of the fuse block to get corroded and lose conductivity. The metal tabs that hold the fuses in place are riveted to the bus work (or individual wires) and those rivets are what make the connection tight. When corrosion gets in between the rivet and the metal parts conductivity is lost or voltage drops too low to operate a small load like a taillight.
By checking to each individual metal piece of the fuse holder you can locate where the voltage is lost. Basically you will need to start at the last known location of voltage and test every single connection. Now an easier way to do this is to put your meter leads on each side of the connection and check for DC voltage. If you find ZERO volts the connection is good. Like putting your positive meter lead on the battery positive post and the negative meter lead on the positive battery cable clamp. A good solid connection will drop no voltage so no voltage can be detected with your meter.

Now if your meter reads some voltage then there is a problem. The higher the voltage you detect the higher the resistance of the connection and the more voltage is lost. For example If you have a connection like the one the red arrow points to (Photo below) and one lead is on the rivet and one lead is on the silver bus piece next to it and your meter indicates 3.2 volts. That means the voltage will drop 3.2 volts there. So If your battery voltage was 12.5 volts all the circuitry after that point would only be 9.3 volts. If one other connection drops 3.5 voltage it will keep your lights from lighting. This problem of voltage loss is not limited to the positive side of the wiring. Every poor ground connection contributes to the voltage dropping. How many ground connections are between the negative battery post and a taillight bulb? 2? 3? 5?

These connections could also have been damaged by an overheated circuit in the past like some of the ones shown below.

I harvested this photo from a post VetteVet posted (Thank you sir) and added the arrows to help show problem areas.

Green arrow rusty connection possible voltage drop where wire is crimped into the metal tab.

Red arrow overheated connection. Notice blackened rivet it has been very hot in the past. Expanding with the heat it deformed and now may be loose. In addition the heat burnt off any anti corrosion coating and it is vulnerable to corrosion.

Blue arrow damaged wire that has been repaired. Properly? You wouldn't know until you took it apart.

Here is the thread where I got the photo from. And once again thanks to our wonderful newly promoted moderator VetteVet!

http://67-72chevytrucks.com/vboard/s...968+fuse+block

That’s a ton of info, I appreciate it! I’ll have to do some more testing and checking things out when I get home. Thanks a lot, I really appreciate it!

[demian5]

Originally Posted by chevymanjt

That’s a ton of info, I appreciate it! I’ll have to do some more testing and checking things out when I get home. Thanks a lot, I really appreciate it!

Do you have the OG turn signal switch? Did you mess with it?

[chevymanjt]

Originally Posted by demian5

Do you have the OG turn signal switch? Did you mess with it?

Yeah when I went to take it off it fell apart in my hands lol. Have one ordered, hopefully I’ll get it soon

[67C10Step]

Originally Posted by chevymanjt

Yeah when I went to take it off it fell apart in my hands lol. Have one ordered, hopefully I’ll get it soon

You'll beat your head to mush trying to get brake lights and the rest with a bad turn signal switch. I disconnected mine and made a poor man setup with a lawnmower battery to check everything past the turn signal switch. Once I had all that wiring and grounding verified as good I went backward from there.

Found melted wires in the intermediate wiring to the rear. Bad fuses, bad turn signal relay, and dirty connections in the bulkhead connection and turn signal switch.

Did all this in 1-2 hour sessions over the course of 2-3 weeks so I didn't lose my feeble mind.

[chevymanjt]

Originally Posted by 67C10Step

You'll beat your head to mush trying to get brake lights and the rest with a bad turn signal switch. I disconnected mine and made a poor man setup with a lawnmower battery to check everything past the turn signal switch. Once I had all that wiring and grounding verified as good I went backward from there.

Found melted wires in the intermediate wiring to the rear. Bad fuses, bad turn signal relay, and dirty connections in the bulkhead connection and turn signal switch.

Did all this in 1-2 hour sessions over the course of 2-3 weeks so I didn't lose my feeble mind.

Yeah I’m just gonna wait till it comes in and get back on it. My brain needs a rest as well