74' FJ40 Won't Start After Harness Swap (Ignition Coil?) (1 Viewer)

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I'll try and share as much information as I can here. The harness in my 74' was absolutely trashed so I had to replace it. My 74' is fitted with a 77' 2F and 4 speed. I sourced a near perfect condition 77' harness and threw it in my 40. Everything works... the blower, the wipers, the hazards, etc. but it will not start.

I have attached the large black with yellow stripe wire to one end of the ballast resistor.
I have attached the other end of the ballast resistor to the positive terminal of the ignition coil.
I have attached the starter bypass wire (black with white stripe) to the positive terminal of the ignition coil. (Green wire pictured was just an extension)
I have attached a wire from the distributor to the negative terminal of the ignition coil. (Red wire pictured)

Some important things to note:

*The truck was running fine with the same setup using the old harness but the only thing I remember is that one end of the ballast resistor was connected to the negative terminal of the ignition coil and the distributor wire was connected to the other end of the ballast resistor. Everything I have read says this is wrong but it ran great!

*I tested resistance across the ballast resistor and got 2 ohms.

*I got 5.8 volts at the positive end of the ignition coil when key was in on position. (The black/yellow stripe ignition wire is hot with key in on position)

*The ballast resistor gets hot with key in on position.

*The white with black stripe wire that branches out of the harness with the ignition wires was bolted to the chassis.

*There is a small black/yellow stripe wire that branches off of the thick black/yellow stripe wire with a condenser attached. I don't know where this goes.

*I have not yet hooked up my alternator but I don't think this would be an issue.

I have wired it like pictured (from 1974 FSM):
wiring.PNG


IMG_3549.jpg


IMG_3550.jpg


Thanks for any input you guys may have. I just can't figure out for the life of me why it's not starting. I feel like I have done everything correctly!
 

Coolerman

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What voltage do you get on the coil + when the key is turned to the start position? It should be full battery voltage if the ballast bypass circuit is working.
Does it even try to hit when cranking over? Have you verified the points are actually working?

You can unplug the coil wire from the dizzy cap, attach a known working spark plug to it, ground the plug then use a clip lead from the coil - and touch it to the battery -. Each time you do this the plug should spark. If it does then you have an issue with the points.
 
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What voltage do you get on the coil + when the key is turned to the start position? It should be full battery voltage if the ballast bypass circuit is working.
Does it even try to hit when cranking over? Have you verified the points are actually working?

You can unplug the coil wire from the dizzy cap, attach a known working spark plug to it, ground the plug then use a clip lead from the coil - and touch it to the battery -. Each time you do this the plug should spark. If it does then you have an issue with the points.

I get 5.77V from coil + when key is in on position. I just realized I only have the negative cable from battery connected to the engine block and starter to frame. Maybe its a bad ground? I think I need to run an additional strap from block to frame.

The points should be working fine as it was running when I pulled the crappy harness out. I will test the points with a test light when I get home.

I pulled the dizzy wire off of the +coil and touched it to the negative terminal on the battery and saw a very light spark jump across to my block from the high voltage wire. It was very light though so I'm thinking bad ground??
 

Coolerman

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My question was: What voltage do you get when the key is turned to START, not run. It should be around +9-10V (not full battery voltage due to the huge current draw the starter requires) when starting IF the ballast bypass on the starter is working. The temporary higher voltage to the coil helps the engine start easier.

You could have a poor ground but if the battery is grounded to the engine and the dizzy has a good ground to the block it should work. The proper way to ground is battery ground to frame, then frame to starter stud.
 
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My question was: What voltage do you get when the key is turned to START, not run. It should be around +9-10V (not full battery voltage due to the huge current draw the starter requires) when starting IF the ballast bypass on the starter is working. The temporary higher voltage to the coil helps the engine start easier.

You could have a poor ground but if the battery is grounded to the engine and the dizzy has a good ground to the block it should work. The proper way to ground is battery ground to frame, then frame to starter stud.

5.77V In on position. 4.8 while starting.

Jumped 12v direct to coil +. Still no start.

Hooked test light to coil - where the dizzy is hooked up and got constant ground. No flash.
 
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I’m no where near the expert that Mark is... but, your “I sourced a near perfect condition 77' harness and threw it in my 40” statement.

Are you sure it’s a ‘77 and not a ‘78? What month/year harness?

The ‘78 has the 10ga PINK Yazaki resistor wire spliced into the 10ga BY (Black-Yellow) wire.

I don’t know what would result by resisting (ballast resistor) the BY a second time... but, that’s the first thought that occurred to me.

The 10ga BY is resisted by the Yazaki resistor wire, in ‘78... the 12-14ga BY wire is NOT resisted. You could feed the small BY (12-14ga) wires to provide full (assuming your battery is fully charged) voltage to the ballast resistor and see if it starts... also measure voltage when ignition in START position.
 
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I’m no where near the expert that Mark is... but, your “I sourced a near perfect condition 77' harness and threw it in my 40” statement.

Are you sure it’s a ‘77 and not a ‘78? What month/year harness?

The ‘78 has the 10ga PINK Yazaki resistor wire spliced into the 10ga BY (Black-Yellow) wire.

I don’t know what would result by resisting (ballast resistor) the BY a second time... but, that’s the first thought that occurred to me.

The 10ga BY is resisted by the Yazaki resistor wire, in ‘78... the 12-14ga BY wire is NOT resisted. You could feed the small BY (12-14ga) wires to provide full (assuming your battery is fully charged) voltage to the ballast resistor and see if it starts... also measure voltage when ignition in START position.

Yes I’m sure. There’s a couple of places that say 77’ on my harness. It also matches up exactly with the color codes on the schematics. I do not have a single pink wire in this harness. Voltage was below 5V in start position.
 
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Have you unwrapped the harness? You would only see the pink about 6-8’ into the 10ga BY, from the front of the truck.

The pink wire does not show up on a wiring diagram (at least none I’ve seen).

‘78 begins in Oct of ‘77 (IIRC).

The pink splice occurs about 8’ into the 10ga BY, from the front of the truck, and is only several feet long. You can’t see it without unwrapping the harness.

Just a thought...
 
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Have you unwrapped the harness? You would only see the pink about 6-8’ into the 10ga BY, from the front of the truck.

The pink wire does not show up on a wiring diagram (at least none I’ve seen).

‘78 begins in Oct of ‘77 (IIRC).

The pink splice occurs about 8’ into the 10ga BY, from the front of the truck, and is only several feet long. You can’t see it without unwrapping the harness.

Just a thought...

Yes I have unwrapped the harness. No pink. Thanks for the thought though.
 
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What’s your battery voltage? Fully charged?

The fact that your ballast resistor and BY wire are hot is concerning (to me). I would suspect a grounding problem... potentially, an energized ground.

I would:

run the battery negative to the frame (normally behind the front passenger side (PS) tire

run the starter body ground strap to the PS frame, almost directly across from the starter

Run a ground strap from the frame to the chassis.

Check your rear harness ground as well... make sure you are grounding the rear harness to the frame (PS), near rear of tranny. It would be really easy to accidentally “ground” a live wire back there.

If you have grounded individual lights to the chassis, and the above doesn’t help, you should check each individual ground.

Good luck!
 
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Messages
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What’s your battery voltage? Fully charged?

The fact that your ballast resistor and BY wire are hot is concerning (to me). I would suspect a grounding problem... potentially, an energized ground.

I would:

run the battery negative to the frame (normally behind the front passenger side (PS) tire

run the starter body ground strap to the PS frame, almost directly across from the starter

Run a ground strap from the frame to the chassis.

Check your rear harness ground as well... make sure you are grounding the rear harness to the frame (PS), near rear of tranny. It would be really easy to accidentally “ground” a live wire back there.

If you have grounded individual lights to the chassis, and the above doesn’t help, you should check each individual ground.

Good luck!

Well the BY wire is obviously hot bc it’s the ignition wire right? And the other end of the resistor goes to coil positive. Which should also be hot no? Battery is fully charged. I’ll double check all grounds.
 

73FJ40

After another night of rust removal!
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@Coolerman :

Congratulations! See post no. 2. "Have you verified the points are actually working?"

You can unplug the coil wire from the dizzy cap, attach a known working spark plug to it, ground the plug then use a clip lead from the coil - and touch it to the battery -. Each time you do this the plug should spark. If it does then you have an issue with the points.
 

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