Blk/yel going in circles?

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

HTC42

HTC42

Joined
Mar 10, 2026
Threads
10
Messages
56
Location
Willamette valley Oregon
1978 fj40, mostly stock but desmogged. This morning, truck would start but not idle. Would run off idle, which made me think fuel cut solenoid. Got to work and was looking at the wiring diagram. That black yellow wire is going all over the place, including the ignition coil. Would not that bypass the resistor and give the coil 12v any time the alternator is charging? I’m confused.
 
I think the black white stripe wire is the bypass wire that offers 12v to the coil during startup. That wire comes off the starter. Blk/yellow is ING.
 
You should be to the solenoid click in and out by turning the key on and off...without starting it.
 
pb4ugo said:
I think the black white stripe wire is the bypass wire that offers 12v to the coil during startup. That wire comes off the starter. Blk/yellow is ING.
Click to expand...
The diagram I printed out

IMG_6206.webp
 
Can you be more specific? What part is wrong? Looking at the basic ing circuit it looks right.
 
HTC42 said:
It shows the Blk/yel ign going to the positive side of the coil
Click to expand...

That is correct. Blk/yellow is the ING circuit.

When the key is in the on position the Blk/yellow wire supplies power and goes thru the resistor to the + side of the coil. When you turn the key to start, the blk/white wire activates the starter. The diagram is not marked clearly, but shows a wire from the ing switch bypassing the resistor and supplies 12v to the + side of the coil during cranking to supply 12v to aid in starting.
 
This is a pretty basic explanation. Maybe you know this. In a points ing, the wire on the -negative side of the coil goes to the distributor thru the points then to ground. The points are nothing more than a switch. When the points are closed, it basically turns on the coil. The power is building energy inside the coil. When the points open it breaks the circuit and its energy is released out the tower of the coil going to the plugs. Electronic ING just eliminates the mechanical function of the points.
 
pb4ugo said:
That is correct. Blk/yellow is the ING circuit.

When the key is in the on position the Blk/yellow wire supplies power and goes thru the resistor to the + side of the coil. When you turn the key to start, the blk/white wire activates the starter. The diagram is not marked clearly, but shows a wire from the ing switch bypassing the resistor and supplies 12v to the + side of the coil during cranking to supply 12v to aid in starting.
Click to expand...
I understand how the circuit works. Great description, though. The diagram I have was drawn by chatgpt…
 
So, as it turns out, my fuel cut/ idle solenoid did take a crap. Any recommendations on which one to buy? I don’t really care about the connector
 
These very rarely “all of a sudden” start running like crap. Usually bad gas, no gas, something else was changed but isn’t brought to light until 18 reply’s later, etc. I’d say, in general, the fuel solenoids don’t just go from working fine to take a dump either.

Have you recently got gas? Have you done anything else? Do you use the choke? A bad fuel solenoid impacts all throttle positions, not just idle. It’s just not many can get it to run long enough to get past idle to tell.
 
brian said:
Grind the tip off and put it back in.
Click to expand...
I wish you had told me that 15 years ago… I like the way you think. I already ordered a new one, but I will do this to the dead one and put it with the trail parts.
 
Skreddy said:
These very rarely “all of a sudden” start running like crap. Usually bad gas, no gas, something else was changed but isn’t brought to light until 18 reply’s later, etc. I’d say, in general, the fuel solenoids don’t just go from working fine to take a dump either.

Have you recently got gas? Have you done anything else? Do you use the choke? A bad fuel solenoid impacts all throttle positions, not just idle. It’s just not many can get it to run long enough to get past idle to tell.
Click to expand...
Non ethanol premium installed by me. Chinese carburetor. I physically verified the solenoid was non functional. This particular solenoid only cuts off fuel to the idle circuit also referred to as an anti dieseling solenoid. I don’t have a choke connected, and haven’t needed one. She was running like a bad a sewing machine a couple days ago. My original intent on this thread was to figure out my disconnect with the wiring diagram I had been using. Sorry if I got a little enthusiastic.
 
You must log in or register to reply here.

Share this page

Back
Top Bottom