Engine and fuse block wiring.

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I openly admit after working in mechanical engineering for a few decades, I suck at wiring and reading wiring schematics. I've lit this poor 40 on fire several times since 1995. Kind of hoping I let out all the smoke already. She's a 1976 but in the lare 90's I pulled a harness out of an unknown year 40 abandoned in a ravine in the mountains. I've got most of the wiring hooked up already due to position and connector type. Near the battery I ha e a thin yellow wire with a black stripe, a thicker white wire and a thicker black with yellow stripe wire. From the schematic it looks like the white wire goes to the +pos battery terminal. I'm assuming this makes its way to the Fuse block as a white with Blue stripe. I can't seem to find the small Yellow black wire on the diagram. There a BY that goes from the started to the coil on the diagram but I've got a Black with wite stripe hooked to the starter. . Any thoughts?

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Nice looking rig. Chilton has all the years wiring diagrams maybe you can find a few options for where your mystery wires come or go.
 
I've got the chiltons, factory diagrams and a fee others. I settled on the white wire going to the pos+. Nothing caught fire but as I leaned on the body and touched a fresh bolt on the fire wall, I got zapped. There's no fused in the block. The only other positive wire hooked up to the battery is down to the starter.
 
Such a nice truck, it would be a shame if something happened to it......

Get your wiring diagram for the year and print it out on 11 x 17 - some folks laminate it.
Based on your description of picking up a random harness, and looking at the condition of some of the visible parts of the harness, I would suggest you meter out (using a multimeter or even a test light) so that you are not guessing where the wires go.
Start at one side of the fuse block, and meter out everything - just looking a the picture, it looks like your starter wire has a break in it.
Go one trace at a time - say, fuse "a" to connector 'b' and then mark it off on your diagram as being checked. and then go to the next one.

There is quite a bit of standard color coding on the Toyota harnesses, but always good to check. green crusties can be hiding inside the harness and connectors.
 
I'm not sure of the yellow with the blk stripe, probably oil sender wire. The white wire goes to the Pos + side of the batt. There MUST be a Fusible link between the batt and the white wire. The white wire goes to the Ammeter, the other side of the ammeter connection is the White/blue stripe wire and I think it goes to the fuse box and I believe in a round about way to the ALT, there's a voltage regulator involved too. White/blk stripe wires are grounds. The B/Y wire is an ING wire. I think the B/W wire is the Start wire to activate the starter. I'd have to get out a Diagram to confirm. You can look on Coolerman's website and find your wiring diagram for your year. Thru thru yrs most of the color codes didn't change much.

 
Here is the real question, do you own a multimeter? Because you can't safely test wires and guess, you need to meter to the fuse block and battery, otherwise you'll potentially have another fire.

Without knowing what harness you picked, it is impossible to truly say which wire does what, but here is the diagrams below, Coolerman made it pretty easy to access/reference. More on that below.
  1. BY from coil changes to BW to starter. It provides full +12v at cranking.
  2. Meter the white wire to the ammeter - if you have continuity, that is your fusible link from battery +
  3. The thinner Yellow Black I'd meter to your oil pressure gauge and see if you have continuity, if so, put a plug and connect to your sender. This is another identifier - if the oil pressure sender wire is by the battery, it is a '76 + harness, if it is on the driver side, maybe early '76 and definitely '75 and earlier.
  4. The thicker BY should go to your coil, which would safely assume it is a 76-77 wiring harness as '78 changed igniter wiring and '75 oil pressure sender would be on the driver side like I mentioned above.
Another quick/easy way to hone in on year is the alternator plug but it looks like yours is modified now - can you take a photo to clarify it?

Another few options are what fuseblock was connected - do you have that? Also wiring coming into engine bay by the carburetor and firewall, there was a number of evolutions that can help narrow down harness year.

 
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BW activates the starter, and feeds 12 volts to the + side of the coil.
 
Here is the real question, do you own a multimeter? Because you can't safely test wires and guess, you need to meter to the fuse block and battery, otherwise you'll potentially have another fire.

Without knowing what harness you picked, it is impossible to truly say which wire does what, but here is the diagrams below, Coolerman made it pretty easy to access/reference. More on that below.
  1. BY from coil changes to BW to starter. It provides full +12v at cranking.
  2. Meter the white wire to the ammeter - if you have continuity, that is your fusible link from battery +
  3. The thinner Yellow Black I'd meter to your oil pressure gauge and see if you have continuity, if so, put a plug and connect to your sender. This is another identifier - if the oil pressure sender wire is by the battery, it is a '76 + harness, if it is on the driver side, maybe early '76 and definitely '75 and earlier.
  4. The thicker BY should go to your coil, which would safely assume it is a 76-77 wiring harness as '78 changed igniter wiring and '75 oil pressure sender would be on the driver side like I mentioned above.
Another quick/easy way to hone in on year is the alternator plug but it looks like yours is modified now - can you take a photo to clarify it?

Another few options are what fuseblock was connected - do you have that? Also wiring coming into engine bay by the carburetor and firewall, there was a number of evolutions that can help narrow down harness year.

Mr. king... or anybody with a stock '75,
I I've got my oil sender on DS but need a pic of how that YB wire is routed.
 

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