Need help with wiring diagram and part location

Can anyone tell me where to find junction box 3B? (see diagram below)

I'm trying to trace the (fried) negative wire from the fuel sender. Am I reading the diagram correctly that there should be a junction block with three relays inside it located between connector BN7 under the seat and the ground bolt (ID) in the kick panel? If so, I can't find that junction box. When I follow the wire from BN7 to the area adjacent to the ground bolt, there is no junction box along that run.

Past the bolt, there are a lot more wires bound in a lot of tape in a hard-to-access area so without digging deeper, I can't tell where the negative wire goes.

Unfortunately, the source I have for the wiring diagram doesn't seem to provide access to the codes or locations. Does the negative wire physically continue past the ground bolt to a junction box behind the dash somewhere and then back down to the ground?

I'm assuming that for the fuel gauge to work properly, it has to go through those relays, else the ground point would be closer to the sender below the bed of the truck. Yes?

I have a separate post explaining the problem and have gotten good help but have not received an answer to this specific question.

Thanks!

 

Here's a full color diagram for 2003 of the combination meter.
J/B No. 3 does not contain any relays, its a junction block. Meaning it just connects wires together.
I also attached the diagram for the locations of the relays and junction blocks

 

Those are not relays.
They are basically jumpers.
They connect multiple wires together.
In your diagram, wires from pins 17,18, and 19 are all joined in the No3 junction box at the 3B connection. They are ground wires.

 

@Stereo in your case you should trace the BR wire back to the junction blocks to make sure you found all the burnt wire. It's not easy to get to them, I suggest pulling the combination meter and center dash vents out to gain access.

 

Have you verified what side of the BN7 connection is the “bad” side?

 

Y-B, GR, and BR are the 3 wires that are coming from your fuel sender in the tank.
Y-B and GR go through BN7 (connector under driver seat) to the combo meter (dash gauge)
BR comes from the fuel sender in the tank through BN7 to J/B No. 3, splits: one leg goes to the combo meter, the other goes to ground point ID

 

WOW! Thanks for all the quick and helpful responses!!

I mistook the 3B symbol for relays. Couldn't Toyota have come up with a different symbol to better differentiate between junction blocks and relay blocks? Geez.

Why are there TWO J/B 3's shown in the illustration in TNShooter's first response? They don't appear to be model specific.

The cause of the short is unknown and may have occurred before I purchased the vehicle used 12 years ago because we never smelled a short. The gas gauge has always worked. The melt was worst at Bn7, both sides, but there is damage at least as far as I can see to the kick plate. I haven't opened the loom under the carriage yet to look for melt along the run to the sender.

Given the extent of the rip-out to get at the wires (or is it relatively easy to remove the combination meter and center dash vents? Any threads?) and my limited knowledge of wiring, I think I may just replace as much wire as I can relatively easily access, put a fuse on it, and hope the circuit manages to keep working. If at some point the fuel gauge ceases to work, I'll just track my miles. I would think to have a shop do this would run over $1000.

 

Why there are 2, I don’t know.
I can only assume there is a difference depending on model. For instance regular cab or extended cab. 2.7 or 3.4 engine.

Maybe someone else know what one is where. But I don’t. I have a 2nd Gen truck, other wise I’d crawl under there look.

 

It's not hard to remove the combo meter and center vents. There are quite a few things you have to take off before you can get the combo meter out though. I believe it starts with the ebrake release, then lower dash panel, then upper dash panel and clock, potentially the steering surround, and then the combo meter?

 

I'm sure I could do it with the help of this forum , but it would take me forever and a day and I need to get my truck back on the road. It's my only vehicle.

Thanks again for everyone's help.

 

The problem with having a shop do it is, most want to do the whole harness. And the harness probably isn’t available any longer. And the shops that would take on the job are going to charge a good bit.

In situations such as yours. One might do just as you are. Get the important stuff working. And live without the ones you don’t need. I can understand that it is going to be really hard with limited information and ability to read diagrams and do the work yourself.

I can probably help you with obtaining the diagrams should you want to try it.
I might even have repair data and test procedures available if you need it.
Just send me a DM should you ever want to try it.

 

@TnShooter, that's an incredibly generous offer. Thank you so much. Hopefully, the gauge will continue to work, but if it doesn't, I may tackle a full repair after our fall camping trips and after we've received the EV we have on order as our second vehicle. (Our daughter received our other car after her car's frame rusted out. Apparently neither I, nor anyone in the Rust Belt where she moved, told her the importance of washing her car. )

 

I think you are better off just leaving it as is. Since it's a ground wire, you essentially have it grounding at any point that is touching the body (that's unpainted). If it had power running through it then you would NEED to fix it, but as long as the gauge keeps working just live with it.

On a side note, my fuel gauge stopped working on my truck years ago. I finally decided to fix it one day. That involved pulling the bed off so that I could get to the sender unit in the tank. I discovered a burnt contact in the connector plug that attached to the sender unit. I have no idea how this happened, but I just repaired the connector and it's been working ever since.

 

It works it has worked since you bought the truck!!

No need to touch things just leave well enough alone .

What ever caused your problem was eliminated before you bought the truck.

Toyota uses a completely different symbol for relays the 3B is just a junction block!

You will learn these things. Best of Luck.

 

I did end up replacing the section I could easily access and adding a fuse but after learning I would have to remove the bed to run a new wire to the fuel sender at the rear and remove much of the front dash to get at J/B 3 where the front half ran before returning to the kick-space ground bolt, I did decide to leave the rest alone.

Thanks again for everyone's help. I really appreciate your patience with a newbie.