Understanding wiring diagram (1 Viewer)

[effjay55]

I am not very good at this stuff, but as far as I understand it there are floating grounds and then there are chassis grounds.
Is the top circled turn signal missing a ground on the diagram or is it a floating ground? And if so, where the heck should I check for the ground?

I know this subject gets brought up a lot, as per my research, but I am still an idiot that can’t figure it out.

The problem:

1. My passenger side turn signal does not turn on with the light switch (parking lights, or with headlights)
2. Turn signal and hazards work, but the bulb is definitely dimmer.
3. If I take off the lense, and add a ground to the bulb housing it works as expected (power probe or a jumper from a nearby grounding point to the housing)

No blown fuses, but pulled them all, cleaned terminals, replaced a few that looked worse for wear.

I can’t really tell from the diagram which side is passenger or driver, not sure it really matters, but this is driving me nuts and I know its probably something stupid like dirt or a bad contact.

I question the diagram missing the ground symbol because I have noticed other errors like….a GB labeled wire all of the sudden is labeled GY… causing major trust issues

 

[pb4ugo]

On early models a lot of the fixture mounting bolts were the grounds. Later models had actual ground wires added to the housings and were bolted to the body/frame. I would recommend adding grounds wires to the fixtures. I pop riveted wires to my rear taillight housings the grounded them to the frame using existing holes or mounting brackets.

 

[mattressking]

If the assembly shows ground off the unit like item 1, it uses the mounting hardware to ground, so you need to clean the metal, threads and ensure bulbs/connections are clean. You can test ground by using a multimeter and connecting the ground circuit of bulb (or housing) to ground (chassis bare metal or battery ground) to ensure continuity. Then verify +12v at the + circuit.

If the ground is part of the wiring harness ( which early trucks really don't do) then you need to chase ground wiring, clean and verify continuity again.

 

[45Dougal]

On early models a lot of the fixture mounting bolts were the grounds. Later models had actual ground wires added to the housings and were bolted to the body/frame. I would recommend adding grounds wires to the fixtures. I pop riveted wires to my rear taillight housings the grounded them to the frame using existing holes or mounting brackets.

Pop rivet sounds like a nice solution - might try that next time - just watch out for bimetallic corrosion i guess.
I soldered my ground wires on to the metal housing which was a challenge tbh, and added nutserts into all the holes to lose the self tappers in favour of M4 screws.
Belt and braces.
Either way a ground wire will add some reliability.

 

[Aloha Jen]

Easy to add ground wires to your front signals and rear tailights just to make sure you have proper grounding. Can run them to the frame or body, or a dedicated grounding spot off the negative battery post like we did. On the front signals we bolted a wire to the metal housing and ran it through the protective vinyl sheath that runs inside the engine bay.

For the rear taillights, we did the same thing with attaching a ground wire to the metal housing and wrapped to in the loom that runs to the front of the engine bay. Also did the same on the license plate lights.

Chasing down grounding issues can be very frustrating and really not make any sense at times.

 

[B y r o n]

According to the diagram the side turn signal is grounded. Since the two turn signal are wired together you should look for the ground on the side turn signal.

 

[effjay55]

On early models a lot of the fixture mounting bolts were the grounds. Later models had actual ground wires added to the housings and were bolted to the body/frame. I would recommend adding grounds wires to the fixtures. I pop riveted wires to my rear taillight housings the grounded them to the frame using existing holes or mounting brackets.

The thing is I don’t see any specified wires coming from either of them that bolt to the chassis, just two wires that go to the socket (from what I can tell anyways). What threw me for a loop was the diagram showing the ground symbol on the bottom, and no ground symbol at the top. Adding grounds seems to be the consensus around here, wondering why its sort of the norm and not the exception though, why are those fixture mounting bolt style grounds so bad??

 

[effjay55]

If the assembly shows ground off the unit like item 1, it uses the mounting hardware to ground, so you need to clean the metal, threads and ensure bulbs/connections are clean. You can test ground by using a multimeter and connecting the ground circuit of bulb (or housing) to ground (chassis bare metal or battery ground) to ensure continuity. Then verify +12v at the + circuit.

If the ground is part of the wiring harness ( which early trucks really don't do) then you need to chase ground wiring, clean and verify continuity again.

What's confusing is that item 1 at the top doesn't show a ground symbol, so I figured it grounds somewhere else? The switch?
Trying to understand where the load finally reaches ground again is a challenge in itself. I was able to add ground to the housing of the non-functioning turn signal using a power probe and it lit up like a Christmas tree… so I know it’s missing a ground… (i … think i know…)

 

[effjay55]

Pop rivet sounds like a nice solution - might try that next time - just watch out for bimetallic corrosion i guess.
I soldered my ground wires on to the metal housing which was a challenge tbh, and added nutserts into all the holes to lose the self tappers in favour of M4 screws.
Belt and braces.
Either way a ground wire will add some reliability.

Ok but does the diagram indicate in anyway that the turn signals (#1) are grounded by way of housing or wire, or are we just left to guess that part?

 

[effjay55]

Easy to add ground wires to your front signals and rear tailights just to make sure you have proper grounding. Can run them to the frame or body, or a dedicated grounding spot off the negative battery post like we did. On the front signals we bolted a wire to the metal housing and ran it through the protective vinyl sheath that runs inside the engine bay.
View attachment 3633206
View attachment 3633213
For the rear taillights, we did the same thing with attaching a ground wire to the metal housing and wrapped to in the loom that runs to the front of the engine bay. Also did the same on the license plate lights.
View attachment 3633219
View attachment 3633210

Chasing down grounding issues can be very frustrating and really not make any sense at times.

Super clean, thanks for the pictures! Really helps me visualize what adding a ground would be like. For some reason I was blowing it out of proportion in my mind . So in your opinion, should I go hunt down a short somewhere, or is it more than likely the housing is failing the ground somehow. It’s starting to seem like it’s likely the latter.

 

[effjay55]

Thank you all for the replies, out of town for the weekend, but I’ll pull the turn signal fixture from the truck on Sunday or Monday to see if I can see anything obvious, and then I might just end up adding a ground to it myself.

Question is though, would adding a direct ground be sort of like ignoring another potential problem, or is it just obviously a housing fixture ground issue and I am just sweatin’ small stuff?

Appreciate you all.

 

[pb4ugo]

I'm quite certain It's a ground issue. It's Very common. You can remove the light clean up the mounting stud and what it mounts too. You'll probably need some rust penetrant. If you want, add a ground wire too.

 

[45Dougal]

The diagrams aren't always 100% accurate, but the lights do all need a ground, so if there's no wire then it must be grounded through the mountings.
Adding an extra ground wire is simply adding another more reliable path to ground - it won't hurt anything.

Certainly sounds like a ground issue because when you turn on the signal, it flashes dimly because it is grounded only through the other filaments (brake or tail light) in that cluster, and back to another ground point at the other cluster. If you look very closely, they might even glow.

This is why using a "continuity tester" can be very misleading, because you might appear to have continuity to ground, while actually you've only got a path through the other filaments.

 

[6f40j9]

Definitely over thinking it. Add a ground wire. Don't worry about what the diagram says.

 

[sleepycruiser]

If it is grounded through the mount, take the mount off and clean the contact areas off…might just be corroded. Or you could run a ground wire and forget about it. I just chased grounding gremlins and it was driving me crazy.

I just got the largest size of this (they are laminated) and through it in a frame and have it in the garage. It is color coded to the wires based on the year.

Toyota

All diagrams include the complete basic truck (interior and exterior lights, engine bay, starter, ignition and charging systems, gauges, under dash harness, rear clip, etc). All diagrams use factory colors including tracers when applicable. All diagrams are laminated in plastic for ease of use...

classiccarwiring.com

 

[effjay55]

I'm quite certain It's a ground issue. It's Very common. You can remove the light clean up the mounting stud and what it mounts too. You'll probably need some rust penetrant. If you want, add a ground wire too.

Thanks, will do!

The diagrams aren't always 100% accurate, but the lights do all need a ground, so if there's no wire then it must be grounded through the mountings.
Adding an extra ground wire is simply adding another more reliable path to ground - it won't hurt anything.

Certainly sounds like a ground issue because when you turn on the signal, it flashes dimly because it is grounded only through the other filaments (brake or tail light) in that cluster, and back to another ground point at the other cluster. If you look very closely, they might even glow.

This is why using a "continuity tester" can be very misleading, because you might appear to have continuity to ground, while actually you've only got a path through the other filaments.

It’s a good sanity check to know that the diagrams aren’t always accurate, at least now I know. I appreciate your explanation of how the ground works in this circuit, and now it makes more sense to me.

Definitely over thinking it. Add a ground wire. Don't worry about what the diagram says.

If it is grounded through the mount, take the mount off and clean the contact areas off…might just be corroded. Or you could run a ground wire and forget about it. I just chased grounding gremlins and it was driving me crazy.

I just got the largest size of this (they are laminated) and through it in a frame and have it in the garage. It is color coded to the wires based on the year.

Toyota

All diagrams include the complete basic truck (interior and exterior lights, engine bay, starter, ignition and charging systems, gauges, under dash harness, rear clip, etc). All diagrams use factory colors including tracers when applicable. All diagrams are laminated in plastic for ease of use...

classiccarwiring.com

Thanks for the response and link, good idea!

 

[ryanwk628]

Try a star washer in your mounting hardware stack to bite through the paint. Also make sure the body is well grounded to the frame (I put a new oversized strap on mine.)

 

[effjay55]

Well that was dumb! There was some surface rust that was messing up the ground on the mounting point. Couldn't really see it behind the washer. Took off the light, cleaned up the rust and everything's good.... Will probably add a ground in the future so I can really seal that area and prevent anymore rust

Anyways now on to the next problem!