Electrical Wiring Loom Build (1 Viewer)

[AYM707]

Now that the Beast is gone, I can concentrate on other projects. My FJ40's electrical wiring is an absolute mess and it drives me crazy. Grounding issues, wires sliced / diced, dead wires just hanging around. I am also considering adding an electrical heater & USB ports; so I need some extra power. I know I can buy a harness, but what's the fun in that!!!

I've read several threads and watch several youtube videos on how to do it. So I've chalked up a plan, so I dont screw it up.

1. Schematic Review
   • Detailed review of the electrical schematic.
   • Identify all switches / devices on the schematic and match them with switches / devices on my FJ40.
   • All wiring to be labelled.
   • Do an electrical calculation to confirm the load / current (fuse rating).
2. Create Test Bed
   • I want to create a test bed, where I will test each circuit to ensure the wiring is correct.
   • Test bed to mirror the schematic, using small bulbs to represent devices.
   • Generic switches to be used. Some actual FJ40 switches may be used.
3. Remove Existing Wiring Loom
   • Carefully remove the existing wiring loom.
   • Each wire to be labelled; showing where it was connected.
4. Install New Wiring Loom
   • Install the new loom.
   • Fingers crossed - hoping I did not screw it up!!

The intent is to post all my work online, so that others may review my work and highlight any issues / mistakes. Also, if anyone wants to build their own loom, they could use my work as a starting point.

This is going to a long / slow project, with Phases 3-4 being in the winter.

 

[AYM707]

Phase 1 - Schematic Review

So I pulled out the most appropriate electrical schematic for my vehicle; an 1982 GCC Spec FJ40 (model FJ40LV-KC). I have attached the file for reference. Grey shaded items do not apply to my FJ40; hence are not going to included in the test bed.

I created a wiring naming standard; and labelled all the wires. Wiring code is as follows :

• Starting point
• Ending point
• Wire colour (as per Toyota) - this will change based on the new wire colours.
• Number & Left/Right

I have the following questions. Refer to the schematic

1. Is this the Resistor located above the Ignition coil?
2. If Hazard Switch is engaged; then Brake Lights & Horn should be energized?
3. What is this resistor? Is this part of the Emission Control Computer?
4. What are these lights? Are these trail hitch lights?
5. Not sure what is happening here?
6. Is this the Hand Brake? Is there a switch/ light at at the hand brake? Is this located below the hand brake; ie below the floor?
7. What is Fusible Link amp rating?
8. Is the Igniter located within the Distributor? Is this the "coil"
9. What is the Inspection Light Socket? Where is it located? I dont think I have this.
10. What is this Condenser? Where is it located?
11. What / where is the Heater Control Indicator Light? What does it do?
12. Why is the cable from the Hazard switch connected to this cable serving the horns? If I'm reading this correctly, this implies that when the Hazard is engaged, the horns will sound.

I would appreciate your input / guidance.

 

[nabbasi]

Having done this for a much older rig, some of my knowledge might not translate.

To add thoughts on 2 and 12, the hazards, horn are powered by the same circuit, but the switch for hazards will send power to the lights for flashing. The horn is powered by the circuit, but the horn relay is what sends the signal to honk (once activated by pressing the horn button on your wheel). Make sure you’re noting the direction the power is flowing. That helped me a lot.

For 4, this is the entire turn signal circuit. Front right and left, dash/ meter right and left, and rear right and left.

For 5, the Blue (L) wire comes out of the fuse panel and the GR wire is spliced into it providing power to the Hazard switch. The L wire goes on to provide power to the wiper motor.

For 6, it looks like a switch to illuminate a warning that the parking brake is set.
Does the GCC model have a floor mounted parking brake lever?

For 9, the inspection light socket is a socket for a work light lamp to plug into. Mine is located beneath the glove box against the firewall.

For the others, mark (coolerman) can answer the fusible link and resistor questions. Shoot him a message. I got a good bit of wiring and connectors from him.

Good luck…this looks like a fun project.

 

[Engineer8000]

I believe #3 depicts the coil for the outer vent control valve.

#7 - the fusible link is sized per the AWG of the wire it protects.

#8 - the ignitor is attached to the coil.

#11 - the heater control lamp is attached to the bottom of the dash and illuminates the heater vent control lever.

 

[AYM707]

Having done this for a much older rig, some of my knowledge might not translate.

To add thoughts on 2 and 12, the hazards, horn are powered by the same circuit, but the switch for hazards will send power to the lights for flashing. The horn is powered by the circuit, but the horn relay is what sends the signal to honk (once activated by pressing the horn button on your wheel). Make sure you’re noting the direction the power is flowing. That helped me a lot.

For 4, this is the entire turn signal circuit. Front right and left, dash/ meter right and left, and rear right and left.

For 5, the Blue (L) wire comes out of the fuse panel and the GR wire is spliced into it providing power to the Hazard switch. The L wire goes on to provide power to the wiper motor.

For 6, it looks like a switch to illuminate a warning that the parking brake is set.
Does the GCC model have a floor mounted parking brake lever?

For 9, the inspection light socket is a socket for a work light lamp to plug into. Mine is located beneath the glove box against the firewall.

For the others, mark (coolerman) can answer the fusible link and resistor questions. Shoot him a message. I got a good bit of wiring and connectors from him.

Good luck…this looks like a fun project.

@nabbasi - thank you for your detailed reply.

Just checking my understanding of your reply.

2 - OK - the horns and the parking lights are typically powered by the alternator; but when the engine is stopped, one can operate the horn & parking brake lights with the key in the Ignition position.
4- OK - these are the Turning indicator lights on the dashboard.
5- OK - Main alternator power going to the Hazard Switch & Wiper system. I have started to add arrows for power direction.
6- Yes, hand brake is floor mounted; but I can't see any wiring. I am assuming this would be like a push button switch, ie when the brake is engaged it would complete the circuit; similar the one on the brake pedal. But I am not sure where it is located; cant see any wiring at the hand brake. We also have a hand brake indicator light on the dash board. I am not sure what's the Brake Warning Switch? I had it in grey, as I assumed it is not standard GGC spec.

Thank you for your support.

 

[AYM707]

I believe #3 depicts the coil for the outer vent control valve.

#7 - the fusible link is sized per the AWG of the wire it protects.

#8 - the ignitor is attached to the coil.

#11 - the heater control lamp is attached to the bottom of the dash and illuminates the heater vent control lever.

@Engineer8000 - thank you for clarifications

7- I might have to do a load calculation to check my fuses and wire load capacities.
8- So my understanding is that Igniter purpose is the break the HV current coming from the Ignition Coil. For my purpose, I am assuming everything in the bubble is contained within Distributor.

Meaning; the wires connected to the Distributor are as follows :

• Grey - HV wire from the Ignition Coil - feeding the spark plugs
• Black - from the Igniter to the Ignition Coil
• Black/Yellow - from the Ignition Switch
• Whit/Black - ground

The Red and White wires are internal, and I'm not touching those. Is my understanding correct?

11- I do not think this is standard GCC spec. Can you send me a picture of what's your's looks like?

 

[Engineer8000]

Information on application of fusible links from the standard. A 16 AWG link would be used to protect a 12 AWG conductor using this guidance.

 

[South Texas 97]

I’ve used these guys with some success for colored wires that match the Toyota standards
Harley Stripe Automotive Wire - 540 Colors Available - Custom Len - https://4rcustomswire.com/

 

[Engineer8000]

Heater control lamp

 

[ijonesinsp]

Where did you get that wiring diagram?

 

[AYM707]

Where did you get that wiring diagram?

there are various sites that have wiring diagrams. Unfortunately, I dont have one for a 1974 FJ40. but look on @Coolerman 's site (Cruiser Wiring - https://globalsoftware-inc.com/coolerman/fj40/WiringMainRightFrame.htm). It has alot of good reference materials.

 

[pb4ugo]

there are various sites that have wiring diagrams. Unfortunately, I dont have one for a 1974 FJ40. but look on @Coolerman 's site (Cruiser Wiring - https://globalsoftware-inc.com/coolerman/fj40/WiringMainRightFrame.htm). It has alot of good reference materials.

Along with color correct wire, terminals ends and plugs.

 

[AYM707]

So I'm trying to understand the start-up sequence, from an electrical prospective. Arrows represent power / current direction.

This is my thoughts :

1. From positive battery terminal, current goes to starter motor. With key in the ACC position; circuit is complete.
2. When key is in IG position, current goes to ignition coil and continues to starter motor; completing that circuit. Power is also going to the distributor. The starter motor cranks the engine.
3. When engine starts turning, the alternator starts to generate power; which sends current to the AV point, where power is distributed to both ST & IG circuits. ACC circuit does not have any power, hence the start motor is no longer cranking.

So when the engine is turning, only circuits ST & IG are energized. ACC is only energized to complete the starter motor circuit.

The part that's confusing me, is that when I turn the key, the engine cracks; ie start motor energizes at the ST position, and stops when the key goes to IG.

Would appreciate your input @Engineer8000 / @Coolerman / @nabbasi

 

[pb4ugo]

Acc is accessories. It powers everything except the ING circuit. When the key is on ING/ON it applies power to everything including the ING circuit/,coil. Then turn the key to start and it applies power to the starter solenoid which engages the starter.

 

[Grayscale]

The wiring diagram has the starter's solenoid energized by the ACC-circuit. And the radio is wired thru the starter circuit.

 

[ijonesinsp]

Along with color correct wire, terminals ends and plugs.

Yes, I have ordered things from him and used the diagrams on his site, but I haven't seen a clean diagram like this one before. Looks like he just has them for a few years.

 

[nabbasi]

Sorry, been out of town taking the family to see a very expensive mouse.

I agree with both @pb4ugo and @Grayscale.

The ACC terminal on the ignition switch should be LR and go to the fuse panel.

The ST terminal is BW and should go to the starter.

Those appear swapped on the diagram.

The ST terminal on the starter should only be energized while cranking. Once it rests in the IG position, the ignition coil (and therefore the distributor) gets power from the BY wire from the IG terminal.

This file (probably from coolerman?) is labeled Haynes manual 1978. It shows the LR / BW wires swapped at the ignition switch your diagram shows. See if this clears up your confusion.

 

[AYM707]

Sorry, been out of town taking the family to see a very expensive mouse.

I agree with both @pb4ugo and @Grayscale.

The ACC terminal on the ignition switch should be LR and go to the fuse panel.

The ST terminal is BW and should go to the starter.

Those appear swapped on the diagram.

The ST terminal on the starter should only be energized while cranking. Once it rests in the IG position, the ignition coil (and therefore the distributor) gets power from the BY wire from the IG terminal.

This file (probably from coolerman?) is labeled Haynes manual 1978. It shows the LR / BW wires swapped at the ignition switch your diagram shows. See if this clears up your confusion.

View attachment 3867138

Thank you @nabbasi / @pb4ugo / @Grayscale for your clarifications - my diagram is wrong. This one makes sense.

 

[AYM707]

So I'm trying to understand the sequence of engine start-up. Also comparing the electrical schematics of the Haynes (left) vs "mine" (right) - [source unknown].

Note - this Haynes is a bit different than the schematic that @nabbasi shared above. That one is very similar to "mine" except an error in the Ignition Switch (which I've corrected here).

There are slight differences, but significant. I have questions on both. Must importantly, which is correct????

Haynes (left) - Assumed Start-up

1. Power (+ve) from the battery goes to the Starter Motor. Separate power signal goes to the Ignition Switch.
2. When Key is in Start position, circuit is completed at the Starter Motor.
3. Starter Motor turns the engine, which engages the Alternator.
4. Key is now in IG position. Power from the Alternator is flowing up into the 15 amp fuse and then down to the Igniter / Ignition Coil. But there is also power coming from the Battery (+ve) through the Ignition Switch, via the IG position. How can you have 2 +ve power streams coming together??
5. High Voltage current then flows from the Ignition Coil to the Distributor / spark plugs.

"Mine" (right) - Assumed Start-up

1. Power (+ve) from the battery goes to the Starter Motor.
2. When Key is in Start position, the circuit is completed at the Starter Motor. But what confuses me is that there is no power source at the Ignition Switch???
3. Starter Motor turns the engine, which engages the Alternator.
4. Power from the Alternator goes to the Ignition Switch.; with Key in the IG position; power goes to the Igniter / Ignition coil.
5. High Voltage current then flows from the Ignition Coil to the Distributor / spark plugs.

There is also a cable connecting the Starter Motor with the (-ve) of the Ignition Coil. I am assuming that power from the Battery is flowing through the Starter Motor to the the Ignition Coil during start-up. But I need some clarifications.

Appreciate your input / guidance.

 

[nabbasi]

Getting deep into it now!

Instead of answering each question specifically, I think the thing that is missing from your sequence is the Ammeter. If you have an Ammeter, its readout shows the amperage being used (by the battery) or generated (by the alternator).

You’ll see on both diagrams that white wire comes from the battery (with a fusible link) that goes to the ammeter, and then the WL wire comes out, splits and goes to the alternator, ignition switch, and fuse panel to power those circuits.

I think if you add that missing link, the starting circuit piece should make more sense.

Voltage Regulator (ext.) / How it works

A lot of you don't like electric stuff and especially not complicated things like an external Voltage Regulator. So maybe it's time to explain how this black box with 3 or 6 wires works. It's really pretty simple. A VR (Voltage Regulator) regulates the charging process of the alternator. Our...

forum.ih8mud.com

Since you mentioned the alternator, the engine turning isn’t necessarily going to do anything from a charging standpoint. That thread explains very well how the voltage regulator works and the role it plays in the charging system.