Electrical Re-wiring / Harness

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Thinking of replacing all the electrical wiring in my FJ40. There are way too many wires, most appear do not connect to anything. Under the dash there are several connectors, not connected and non-standard wires. Planning a big trip and dont want any electrical / earthing issues. Also need to add a few charging points.

I have studied the wiring diagram and seen a few diy youtube videos. Plan is to make a new electrical harness and then switch it with the cables in the vehicle.

Quick basic questions :
1- What is the recommended wiring gauge? Is it different for the alternator (its a thicker cable on my FJ40 - not sure if standard?)
2- There is a fusible link from the battery to the amp meter. What amp should that be?
3- Should i remove the original connectors? or would it be just better to connect to the old wire before the connector?
4- Need to add a few charging points, assuming 15 amp would be sufficient (same as a lighter).

Would appreciate any advice / guidance on this project.
 

Coolerman

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I would HIGHLY recommend you not try to replace the OEM harness entirely if the wires are in good shape. Instead simply remove the wires you do not need for your particular application.
Toyota harnesses use several gauges of wire depending on the circuit.
10 ga for the alternator charge B+ wire
10 and 12 gauge for power feeds to fuse panel, key switch and ignition
14 ga for head light wiring and cigar lighter
16 ga for tail lights, turn signals, reverse lights, wipers, horns
18 ga for meter lights, meter gauges, emissions wiring, sensors

When messing with the harness you will want to get the schematic for your year.
Now label the connectors so you know where everything goes.
Remove the harness from the truck and lay it out on a piece of 4' x 8' plywood.
Now you can un-tape it, remove any wiring you do not need, repair any wiring that needs it, add any wiring like your power ports, tape it back up and re-install it.
 

Engineer8000

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Buy a good open barrel crimp tool, terminals and connector bodies to fix any issues with connectors. Most connector bodies are still available new.
 

ToyotaMatt

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Thinking of replacing all the electrical wiring in my FJ40. There are way too many wires, most appear do not connect to anything. Under the dash there are several connectors, not connected and non-standard wires. Planning a big trip and dont want any electrical / earthing issues. Also need to add a few charging points.

I have studied the wiring diagram and seen a few diy youtube videos. Plan is to make a new electrical harness and then switch it with the cables in the vehicle.

Quick basic questions :
1- What is the recommended wiring gauge? Is it different for the alternator (its a thicker cable on my FJ40 - not sure if standard?)
2- There is a fusible link from the battery to the amp meter. What amp should that be?
3- Should i remove the original connectors? or would it be just better to connect to the old wire before the connector?
4- Need to add a few charging points, assuming 15 amp would be sufficient (same as a lighter).

Would appreciate any advice / guidance on this project.


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I would HIGHLY recommend you not try to replace the OEM harness entirely if the wires are in good shape. Instead simply remove the wires you do not need for your particular application.
Toyota harnesses use several gauges of wire depending on the circuit.
10 ga for the alternator charge B+ wire
10 and 12 gauge for power feeds to fuse panel, key switch and ignition
14 ga for head light wiring and cigar lighter
16 ga for tail lights, turn signals, reverse lights, wipers, horns
18 ga for meter lights, meter gauges, emissions wiring, sensors

When messing with the harness you will want to get the schematic for your year.
Now label the connectors so you know where everything goes.
Remove the harness from the truck and lay it out on a piece of 4' x 8' plywood.
Now you can un-tape it, remove any wiring you do not need, repair any wiring that needs it, add any wiring like your power ports, tape it back up and re-install it.
Thank you for all the detailed info.

Knowing your experience...your advise not to pull the entire harness out...has been weighing heavy on my mind. Problem is that there are too many cut wires with bad joints all over. I'm also have electrical issues; overall electrical system works sometimes...

Hence, think I need to plow ahead....I got the wiring plan (SLD) and got collecting the tools / wires for the project. As long as I work slowly and systematic / label everything carefully. Just need to source matching connectors.
 

73FJ40

After another night of rust removal!
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@AYM707

You must re-read post #2.

"Now label the connectors so you know where everything goes.
Remove the harness from the truck and lay it out on a piece of 4' x 8' plywood.

Now you can un-tape it, remove any wiring you do not need, repair any wiring that needs it, add any wiring like your power ports, tape it back up and re-install it."


Hopefully the wiring diagram you have for your truck is accurate for your specific model year. Every diagram I found for my 73 FJ40 was either for an earlier year, a later year, or a mix of different years that did not reflect the actual wires in my harness.
 
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Really check that your year matches the diagram. Mine is a Jan 1972 but the schematics I have to use are for the 1971 model... mine changes schematics in Sept 1972... they are DIFFERENT.
 
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@AYM707

You must re-read post #2.

"Now label the connectors so you know where everything goes.
Remove the harness from the truck and lay it out on a piece of 4' x 8' plywood.

Now you can un-tape it, remove any wiring you do not need, repair any wiring that needs it, add any wiring like your power ports, tape it back up and re-install it."


Hopefully the wiring diagram you have for your truck is accurate for your specific model year. Every diagram I found for my 73 FJ40 was either for an earlier year, a later year, or a mix of different years that did not reflect the actual wires in my harness.
Hi @73FJ40

That's what I was planning.

I have also been thinking I should just buy an OEM harness kit and then modify that to suit. On another thread, there was a reference / link to the Painless kit, which is not available.

Found this on e-bay :
for $300; but unsure if its for a FJ40 or Ford Bronco? I've seen the same harness on a few web sites.
 

73FJ40

After another night of rust removal!
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@AYM707

When I read your response in post #5, above, to @Coolerman :

Knowing your experience...your advise not to pull the entire harness out...has been weighing heavy on my mind. Problem is that there are too many cut wires with bad joints all over. I'm also have electrical issues; overall electrical system works sometimes...

I was under the impression you failed to understand Coolerman's advice to remove the entire harness after marking all the connections.

My mistake.
 
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@AYM707

When I read your response in post #5, above, to @Coolerman :

Knowing your experience...your advise not to pull the entire harness out...has been weighing heavy on my mind. Problem is that there are too many cut wires with bad joints all over. I'm also have electrical issues; overall electrical system works sometimes...

I was under the impression you failed to understand Coolerman's advice to remove the entire harness after marking all the connections.

My mistake.
no problem buddy.

I recognize this would be a major undertaking. Doing my research as this has to be done very slowly and carefully. A lot of planning first, than execution.

My plan
1- First photograph connection.
2- Label the connectors.
3- Lay the old harness on a table (isolated in a corner).
4- Than cleaning old harness. More labels for wires as you go. use zip ties to wires together.
5- New connections / wires where necessary.
6- Test everything with a battery. Then re-install it back.

Thinking this should take a month, working weekends only.
 
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I made an entire new harness using wire and connectors bought from Coolerman for my 65. I estimated that it probably took me 30-40 hours. Time-consuming but not at all difficult.
Thinking of making a new parallel harness too
 

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