wire gauges in 76 harness (1 Viewer)

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couple things so I'm curious what are the 3 different gauge sizes predominantly used in my truck? I think its 12 14 and 16 but I would like a confirmation on that.
With regards to connecting wires - what's the rule with bigger to smaller?
And then in regards to just wiring in general im curious about making sure correct wire gauges were used by my PO with certain wires in place... Im following my Haynes/Coolerman Wiring diagrams while adding in new wire for accessories taken out of harness - so one question is how do I know where to use what size gauge? and what size gauge is proper for what function?
Im posting on a different thread also about this, but this is what im trying to figure out: my Green/Red wire situation between my Hazard plug, Light Switch, and Fuse box. Between all the Green/Red color coded wires there are 2 sizes which I believe are 14 and 16. Wiring diagrams don't have 2 Green/Red wires going straight to Hazard plug as my rig Does - it shows one going straight there that's protected by a 15amp and then one protected by a 20amp that does ultimately connect to the hazard plug but it goes through the horn relay / stop light switch/ and something else first (Which mine Does Not). And then finally the light switch has a Green/Red that goes to it from fuse box protected by a 15amp. So I need to straighten that out by figuring out which Green/Red on the fuse block needs to run through the horn relay/stop light switch/coolingfantimer and what size that wire gauge should be? And, how do I know which size gauge to use between the three )
 

M1A1cruiser

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It occurs to me that my rambling below didn't answer your primary question about which gauge to use between fuse box, switches and lights.

I believe everything downstream of the fuse box is 16ga. Read on at your whim/peril.


I'm going to try to address the G/R dilemma here, rather than in your electrical build thread because I think it'd be easier to ramble here rather than clog up the progress being documented there.

Having rebuilt exactly one wiring harness, I'm not an expert. But I will say I learned a ton taking the whole thing down and working/tracing/asking questions and ultimately getting CLOSE to understanding some of the circuits.

I'm not surprised that there are multiple fuses that feed into your Hazard S/W. On mine the STOP/HORN (15A) fuse and the TURN (20A) fuse both run wires into the hazard S/W. You'll notice that the STOP/HORN fuse is fed by constant power, thus your brake lights and horn will work even when the key is off. Also, the flasher is wired 'down stream' of the hazard S/W so power has to go through the hazard S/W, through the flasher, through the turn signal stalk (on the column) then out to the lights for your turn signals to work. This path is NOT the case for brake lights.

I hope that might clarify why you have multiple colors of the same wire going through your hazard S/W - those same colors are viewed by Toyota as part of the same system (brakes, turn signal, hazard, whatever...) so the same color is (somewhat) maintained through the path from battery to fuse to switch to light.

Take your time. Trust the wiring diagram. And post up when you have questions. I noticed you highlight pictures of the wiring diagram where you're working. That's super helpful when asking these questions. It really doesn't allow anyone to comment on a picture of wires that who-knows-what has been done over the years.

As for gauges of wire, I seem to remember I used 10 for the main trunk wires (the W/L and B/R off the ALT and BATT), 12 for grounds, and.... maybe...? 16 for the switches and lights. I think I over did it a little, but seemed like a good idea to be more robust than not. Perhaps one of the electical gurus will be able to chime in on the actual (stock, original) wire sizes, but that's my two cents.

Hope to help. Good luck with it.
Travis.-
 
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Joined
Feb 5, 2019
Messages
492
Location
Bay Area California
It occurs to me that my rambling below didn't answer your primary question about which gauge to use between fuse box, switches and lights.

I believe everything downstream of the fuse box is 16ga. Read on at your whim/peril.


I'm going to try to address the G/R dilemma here, rather than in your electrical build thread because I think it'd be easier to ramble here rather than clog up the progress being documented there.

Having rebuilt exactly one wiring harness, I'm not an expert. But I will say I learned a ton taking the whole thing down and working/tracing/asking questions and ultimately getting CLOSE to understanding some of the circuits.

I'm not surprised that there are multiple fuses that feed into your Hazard S/W. On mine the STOP/HORN (15A) fuse and the TURN (20A) fuse both run wires into the hazard S/W. You'll notice that the STOP/HORN fuse is fed by constant power, thus your brake lights and horn will work even when the key is off. Also, the flasher is wired 'down stream' of the hazard S/W so power has to go through the hazard S/W, through the flasher, through the turn signal stalk (on the column) then out to the lights for your turn signals to work. This path is NOT the case for brake lights.

I hope that might clarify why you have multiple colors of the same wire going through your hazard S/W - those same colors are viewed by Toyota as part of the same system (brakes, turn signal, hazard, whatever...) so the same color is (somewhat) maintained through the path from battery to fuse to switch to light.

Take your time. Trust the wiring diagram. And post up when you have questions. I noticed you highlight pictures of the wiring diagram where you're working. That's super helpful when asking these questions. It really doesn't allow anyone to comment on a picture of wires that who-knows-what has been done over the years.

As for gauges of wire, I seem to remember I used 10 for the main trunk wires (the W/L and B/R off the ALT and BATT), 12 for grounds, and.... maybe...? 16 for the switches and lights. I think I over did it a little, but seemed like a good idea to be more robust than not. Perhaps one of the electical gurus will be able to chime in on the actual (stock, original) wire sizes, but that's my two cents.

Hope to help. Good luck with it.
Travis.-
Appreciate it
 
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Jan 22, 2007
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Alva, Fl.
You might try getting a FSM wiring diagram for your vintage truck(build date). Toyota made changes to the wiring color codes based on function, so a build date different than yours may have a "red w/yellow stripe wire connected to a redw/white stripe wire---or even a a black wire(on the other end of the part it fed), depending on the function---I have not seen wire gauge ever indicated on the diagrams(at least not that I can discern)---BTW--these wire color changes would be a great sticky!!
One constant seems to be the ground wire--it is ALWAYS white w/black stripe
My Haynes manual and FSM disagree on colors-'course I'd opt for FSM----it is closest to what I actually have
 
Joined
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my diagrams are good - I think im more interested in the gauges of the wire utilized and how to know which was utilized where - I dont trust what has been done previously to me.
And can you attach different size gauges together as long as the smaller (higher number) gauge is downstream? or do I have that backward
 

Engineer8000

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SOUTHPORT NC
I think the design standard is to keep voltage drop < 3% from the alternator to the end device. Remember DC voltage drop is round trip so you have to double the distance from the device back to the source. There are some on line dc voltage drop calculators. This SAE standard should help you identify what wires you have. I also have this chart that I found a while back

1618679572528.png
 

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