Confusion on ignition system wiring...

[misterW]

I have a 91 3.0 which has had erratic periods of no starting. Most of the time it started...except when I needed to be somewhere. I THOUGHT I had found the answer, but after looking over a trouble shooting manual, I am confused.

I had previously tested the 12v red and green power wire going to the coil and it had been fine when tested. This time, however, I tested it when the key was in the START position, instead of the RUN position, like I had done before. And this time, I didn't get any voltage. I thought this must be the answer -- how could it spark without power to the coil? I jumped a wire to the red and green power wire to see what would happen and the truck started. Seemed like the problem was solved.

But while tracing the course of that red and green wire, I looked at a trouble shooting manual for the truck and it appears to say that the red and green wire circuit is closed only in the RUN position. How does that make any sense? How can the truck start without power going to the coil? am I misreading this? I attached the chart from the trouble shooting manual below.

 

[RonD]

Just to be clear

Engine cranks every time(starter motor works), it just won't fire up and you think its spark related not fuel related

Here is a diagram of 3.0l ignition(spark) setup: https://www.therangerstation.com/tech_library/EDiagrams/files/Diagram_Ignitionsystem_1990_3_0.JPG

Yes, the red/light green wire powers the coil, but has 12v in RUN and START from ignition switch

Its possible the ignition switch under the steering column is worn out and not powering the brown/pink wire(I2) that is spliced to the red/light green wire, or splice is bad

 

[misterW]

Thanks, Ron! Yes, at least in part spark related because I had been grounding a spark plug and not getting a spark. And it did spark and start when I jumped 12v to the red/light green wire. And yes, I see what you mean about the brown/pink wire. That would actually make a lot of sense because it would help to explain some other issues that I had wondered if they were somehow related -- door chime and various gauges not working properly. Following the path of that brown/pink wire, it looks like it energizes a number of those things eventually. Wonder how easy S206 is to get at.

 

[RonD]

Splice 206 should be close to ignition switch but never looked for it

You would need a 1991 Ranger EVTM to ID its location without hunting around for it

EVTM - Electrical & Vacuum Troubleshooting Manual

Ford sends these out to every Ford service department every year for every model, its part of shop manual set but always sold/found separately, its the most used book in the set, lol

 

[misterW]

Thanks Ron,
It turned out to be not the splice but a wiring issue at the ignition switch with the brown and pink wire. That damn thing had been responsible for the inconsistent starting for quite a while.
Next question: I'm putting in some toggle switches to replace the factory ignition switch. What amperage do you think would be sufficient for the switch for the Red/Light Green ignition circuit wire?

 

[RonD]

20amp switches with 15amp fuse on each

 

[misterW]

Thanks!