The "Official" FJ25 Wiring Harness Thread

[Coolerman]

Well I had some time over the holidays in between day job, wiring harness building, and contest story writing , to actually un-box and start documenting the FJ25 wiring harness I was sent.

Here is the harness as it was received:

 

[Coolerman]

The harness is in pretty good shape considering its age!

My wiring shop is in my basement where it stays about 55-60 degrees year round. These cool temps were not helping me untangle the harness! The first thing I did was to heat it up a bit to make it relax from being "rolled up" for shipping . I simply hung it up over top of a propane heater for about 10 minutes. This made it really easy to unroll it and stretch it out so it could be un-taped. It also helped soften the adhesive on the places where it had been re-taped over the years. The adhesive had dried up long ago on the original tape...

The first thing I noticed was that this harness had been left in place while the FJ25 was painted...TWICE! Once with green and later with beige. This made it hard to see what wire color was what in some areas.

I started un-taping the harness and was met with my first surprise: There are only four wire colors used in this harness! Red, Green, Yellow, and Black! (Remember I had never seen one of these before this...)

The second surprise was that Toyota used string to bind the harness instead of tape like on later harnesses. I guess string was cheaper than tape at the time?

No wonder folks have so much trouble when trouble shooting these older trucks! Without a schematic and some knowledge it would be hard to tell which green wire was which...

 

[Coolerman]

It was about this time I noticed a lot of terminals, and some wires going into connectors, had colored heat shrink tubing on them. Heat shrink tubing was around in the late 50's early 60's? Yep! Turns out that heat shrink tubing was invented in the 50's by RayChem. I guess Toyota decided to put it to good use. A quick look at the colored schematic (excellent work on that BTW!) I had verified the colored tubing was used to help identify circuits. That knowledge makes it a bit easier to follow the wiring. I finished un-taping the harness and took this pic of the fuse block to show the painted wires:

 

[Coolerman]

Here is an overall shot of this harness:

 

[Coolerman]

Now that it was un-taped it was time to mount it to a jig board. I use a 4x8 sheet of plywood to mount the harnesses. Velcro and staples are used to secure the harness to the board.

 

[Coolerman]

Now that it is mounted I can start the documentation process. I will use the colored schematic and verify this harness matches it. If it does not I will post the differences. I will start at one end, choose a wire and trace it through the harness to its final destination. Then I will create a circuit sheet (like for instance the Horn Circuit) showing every wire and connection involved in that circuit. That sheet will be used to create a Build Sheet for that circuit which will be used later when constructing new harnesses.

Yes, it's a lot of work! I put in over 100 hours documenting the 1978 FJ40 wiring harness!

Some things I have noticed so far:

1. The wire used seems to be WAY bigger in some circuits compared to later harnesses. I need to do some load calculations to verify this, but 14 ga wire for a turn signal seems to be overkill?

2. The wire used is NOT the same as was used in later harnesses. Unless this harness has been in a box and not exposed to the elements, it should be brittle. Especially wires that are in the engine compartment. This harness is very supple leading me to believe the wire coating may not be the typical Toyota GPT plastic wire coating.

3. Lack of fusing has me puzzled. There are 5 fuses but only three seem to be used?

Anyway, that is all for now. I will post more when I get more into the documentation.

 

[Old Red]

Thank you for doing and sharing useful stuff.

 

[mmcinnis]

Now that it is mounted I can start the documentation process. I will use the colored schematic and verify this harness matches it. If it does not I will post the differences. I will start at one end, choose a wire and trace it through the harness to its final destination. Then I will create a circuit sheet (like for instance the Horn Circuit) showing every wire and connection involved in that circuit. That sheet will be used to create a Build Sheet for that circuit which will be used later when constructing new harnesses.

Yes, it's a lot of work! I put in over 100 hours documenting the 1978 FJ40 wiring harness!

Some things I have noticed so far:

1. The wire used seems to be WAY bigger in some circuits compared to later harnesses. I need to do some load calculations to verify this, but 14 ga wire for a turn signal seems to be overkill?

2. The wire used is NOT the same as was used in later harnesses. Unless this harness has been in a box and not exposed to the elements, it should be brittle. Especially wires that are in the engine compartment. This harness is very supple leading me to believe the wire coating may not be the typical Toyota GPT plastic wire coating.

3. Lack of fusing has me puzzled. There are 5 fuses but only three seem to be used?

Anyway, that is all for now. I will post more when I get more into the documentation.

I really hope that this is going to work out, im only saying this because everything else on the truck has been a hack job from the many PO's. Looks great thanks for documenting this. Mike

 

[Splangy]

3. Lack of fusing has me puzzled. There are 5 fuses but only three seem to be used?

Anyway, that is all for now. I will post more when I get more into the documentation.

There appears to be four fused circuits being used in your photo of the fuseblock. Note the bus bar on the right side of the block. That's the current source side.

Here's a photo of my fuseblock and of the FJ25 wiring diagram.

 

[Cruiser_Nerd]

You are spot on for your #1,2&3 observations. Insulation does not seem to dry out. Don't forget the yellow and white streamer outside the wrap, always look for that in an original.



Splangy's #4 down fuse illustrates the absurd fuel circuit which really goes power-switch-gauge-fuse-sender-ground.

#3 down is typically used for switched accessories like heat or wipers, I do not believe mine had the top three common. I posted a scan of the fuse card somewhere I'll look for it later.

The other one to be aware of is the stop light circuit which is shown on the diagram and physically there to run a separate stop light (not combination stop/turn). This needs to be reconciled with the original turn signal switch and aftermarket switch which is utilizes the combination light. I repurposed that wire for a reverse lamp.

 

[Cruiser_Nerd]

Fuse Card Thread:



I have my reverse light on #3 and the wipers on #5.

 

[Coolerman]

[QUOTE="Splangy, post: 10747665, member: 47065"

There appears to be four fused circuits being used in your photo of the fuseblock. Note the bus bar on the right side of the block. That's the current source side.

Here's a photo of my fuseblock and of the FJ25 wiring diagram.[/QUOTE]

Thanks for the clear schematic and pic of your fuse block. Your colors match the ones I found after using some Acetone to remove some of the paint from this one. There is a jumper wire, that was not OEM, installed from the bottom fuse up to the third fuse. I have removed that, so there are only three fuses being used.

 

[Coolerman]

All 15 amp huh? That makes it easy to populate! Thanks for that pic.
So where is all your harness wrap?

 

[Coolerman]

I am considering a few options for anyone who may want a new harness built down the road:

Pure OEM. This would include OEM wire sizes and colors and colored heat shrink where it was used. Wire used would be GXL or possible SXL like I use now. This option is for anyone doing a true restoration.

Pure OEM Electrically but using properly sized wire for each circuit and later GXL colored and striped wire in the circuits. Like GW for brakes and Red/Yellow, Red/Green for headlights that kind of thing. Not sure anyone would even want this version as it really has no true benefits. Though it would be easier to trouble shoot.

Custom: Using properly sized wire for the circuits and later GXL colored and striped wire. Re-doing the fusing to better protect more circuits in the harness and adding a fusible link for the main power wiring. Would still use all OEM switches, connectors and terminal blocks. This would be for anyone who actually drives their truck and doesn't want it to burn to the ground.

Give me your opinions and ideas...

 

[BTUMAN]

I would offer that using the SOR rear tails lights with the dual filaments allow for a more safe and modern light system for the rear. I had mine completely rewired and had the rear tails so they were Stop, Running and Blinker- while still keeping the rear licence lamp. For the really old FJ25s, there was only the rear licence lamp that was also a single break lamp like a Model A Ford. The larger were only for turns I understand. Anyway- I guess that could be the upgraded version.

 

[Cruiser_Nerd]

So where is all your harness wrap?

What's the first thing you did to figure it out? Wrap is waiting on the restoration..........

For the brake lights I would not bother with the separate brake light version. Just saying the wire is there, but not used.

Idle thought. The large wire size may have been a holdover from the 6V days? Extra material was probably cheaper than a production change......same for making changes to the pesky diagram print.

 

[Coolerman]

Rear chassis wiring can be anything you want. Pure OEM, use later model dual element lights, or even the three way modern lights with separate reverse, turn, and brake/park. That last one would require a bit of tinkering with the turn signal wiring. I can even add Hazard lights using a later 69-72 switch if you need them.

However before I start building custom harnesses, I need to finish documenting the OEM harnesses!

The real question is will most folks want OEM harnesses? The reason for that question needing to be answered now? I am looking at what wire would have to be ordered in and it would be several hundred dollars of those four colors in several different gauges. Colors and gauges I can not use anywhere else. If I replaced the four colors used in the FJ25 with the later Toyota wire colors and gauges I would not have to order anything new...

 

[Cruiser_Nerd]

Not speaking for others, but I would be happy with modern wire and gauge in close to stock colors snd form....... If I needed one.

 

[pardion]

Not speaking for others, but I would be happy with modern wire and gauge in close to stock colors snd form....... If I needed one.

I agree with Cruiser_Nerd .

 

[1MAC]

I don't have an FJ25, but I'm thankful there's a guy like Coolerman out there taking on projects like this. He was a great help when I made all new harnesses for my 65. We are so lucky he's a part of the Land Cruiser world.