Help me understand my ignition circuit (1 Viewer)

[CaliColin]

Can someone tell me what the circuit looks like? I know I have a neutral safety switch and the ignition switch somewhere in there, and then after that, is it just grounded to complete the circuit? Is there no starter relay involved?

 

[Rusty Marlin]

Like you suspect its basically switches and grounds; start with a search for...
FSM for a hell of a price
It will tell where they are.
Sounds like an intermittent grounding problem.

 

[jonheld]

'91 wont start,crank or even click

My 91 has sat for a while but i need to get it going for this winter, however it has always started. last time i started it was a couple months ago and a trans line blew when i shifted into drive. i have now repaired that issue and now when i turn the key nothing happens. i have power...

forum.ih8mud.com

A search on "starter circuit" will set you free.

 

[nemoblackdog]

That diagram can't be correct (even if incomplete) if it still sometimes starts with just the key alone. The way you've drawn it up there is that the momentary button must always be closed for it to start. I don't think that's what you're describing.

If I had to guess, I'd say that button is in parallel (bypasses) the normal ignition circuit to the starter, but the original starter circuit is still actually in place. If that's the case, then it could be as simple as the other end of that wire (where the question mark is) just goes to the (+) terminal of the battery.

 

[jonheld]

Can someone tell me what the rest of the circuit looks like?

I can't watch this thread anymore. It's too painful.
Here is the schematic for the starting circuit. It is very simple and doesn't rely on any other system, as previously described in my last post.

 

[nemoblackdog]

That's the factory circuit, and doesn't say anything about what the previous owner did to modify it. It could be largely intact, or significantly modified. No way to tell, really, without digging in to the actual wiring that is present in the truck.

 

[CaliColin]

Thank you for the wiring diagram. I understand about 40% of it, but enough to ascertain where the Neutral Start Switch and Ignition Switch are along the circuit. The threads I've encountered through searches (yes I did a search) were likely discussions of the 1993+ 1FZ engine and leading me down wrong bunny trails.

nemoblackdog you are correct that the momentary button is actually in parallel with the normal ignition circuit. That occurred to me later that night looking at the diagram, and is the only way it would work. All other wiring on the truck looks legit, other than the momentary bump switch. Fortunately that is easily corrected.

 

[nemoblackdog]

There's definitely a good number of us who've used a separate solenoid or relay (which is what I did) to bypass the ignition circuit. I don't know if the diagram that @jonheld posted is from a 3FE engine, but I would suspect so since I think he's one of the main 3FE experts here. If so, then it's virtually identical to the circuit on the 1FZ and any decision you make for remedying this (repair, replace, bypass) can be done on one just as easily as the other.

BTW, this sort of bypass has a lot of history in other vehicles (Toyota mini-trucks, GM vehicles and VW bugs.) I used a relay instead of a solenoid, but certainly either would work. A 30/40A relay is a smaller package and should be more than sufficient for this task.

Of course the other option is to diagnose the root cause and restore the stock ignition circuit to like original condition. That's a valid approach but I will put out there that it is possible that the root cause might not be individual components like switches or connectors, but could be in the wiring and splices, which is harder to repair. There's a lot of other threads about this in the forum.

 

[CaliColin]

Thanks for the help you and jonheld have given in this pursuit!

 

[Howard705]

on my '94 it was neutral safety switch Very slightly out of adjustment. IDK if these the same.

 

[CaliColin]

on my '94 it was neutral safety switch Very slightly out of adjustment. IDK if these the same.

Thanks for that. I located the NSS and inspected the connections.

 

[Howard705]

Thanks for that. When I experienced my last no-crank episode, i was prepared for it and jiggled the gear shift lever, moved it to N, tried to start, and back to P and tried again with no change. I also located the NSS and inspected the connections. It looked clean on the transmission side, fwiw.

This was while still getting 12 volts at starter during crank, replacing starter, was VERY intermittent.

 

[Seth S]

Often the old wires that are used to trigger the solenoid on the starter have deteriorated enough so that they cannot carry enough current to trigger the hot solenoid. One trick is to simply install a Ford/GM style fender mount starter relay (costs about $20). You can use the stock wiring to be the trigger on this new relay and then run brand new heavier gage wire from the battery to the fender relay and from there to the same terminal your old wiring went to. This keeps the stock key working and all you are doing is basically triggering a new relay which in turn triggers battery voltage to the starter solenoid but now on new heavier gage wire which help solve the current draw issue on a hot starter solenoid. You are basically replacing the momentary button circuit with a cleaner version that lets you stick with the key setup.

 

[CaliColin]

Often the old wires that are used to trigger the solenoid on the starter have deteriorated enough so that they cannot carry enough current to trigger the hot solenoid. One trick is to simply install a Ford/GM style fender mount starter relay (costs about $20). You can use the stock wiring to be the trigger on this new relay and then run brand new heavier gage wire from the battery to the fender relay and from there to the same terminal your old wiring went to. This keeps the stock key working and all you are doing is basically triggering a new relay which in turn triggers battery voltage to the starter solenoid but now on new heavier gage wire which help solve the current draw issue on a hot starter solenoid. You are basically replacing the momentary button circuit with a cleaner version that lets you stick with the key setup.

Yes. This.

 

[Seth S]

Yes. This. Exactly what I’ve read others have done, and what nemoblackdog mentioned he did above for his rig. In my searches I’ve mostly encountered ‘93+ 1FZ engine owners and so I began to map out my own solution for my lowly ‘91 3FE. The diagram that jonheld graciously provided gets me a little closer to figuring out how to wire the bypass solenoid. Which I will execute only if “getting back to stock” doesn’t yield a reliable start circuit. The super intermittent nature makes it extremely difficult to nail.

first thing you could do is replace the stock wiring that feeds power from the battery to starter solenoid and likely replace any old connectors or fusible links.

 

[blkprj80]

You would want the EWD to locate all the splices in the drawing @jonheld provided.
If it's intermittent, a bad splice is possible.
When it fails, you should be able to "inject" 12V (through a 15A fuse if you can) to the various points along the circuit. If you play with it while it's working, you will get a feel for how to do it at various places. Back of ignition switch, at the neutral safety switch, etc. Then when it fails, see how it reacts to the same.
Note the starter solenoid will cause the wire to spark when it contacts. Don't be afraid, push it and hold it firm for 2 seconds. The starter should spin.

As stated, your switch isn't wired as you show. A switch needs to close to actuate the circuit. Your switch is wired in parallel to the original truck wiring.

Here's a quick sketch showing the path you need to follow.
The red is how your pushbutton switch is wired, although it doesn't seem to be attached to your starter like I show. Do you have a picture of your switch and how it's wired?

 

[CaliColin]

You would want the EWD to locate all the splices in the drawing @jonheld provided.
If it's intermittent, a bad splice is possible.
When it fails, you should be able to "inject" 12V (through a 15A fuse if you can) to the various points along the circuit. If you play with it while it's working, you will get a feel for how to do it at various places. Back of ignition switch, at the neutral safety switch, etc. Then when it fails, see how it reacts to the same.
Note the starter solenoid will cause the wire to spark when it contacts. Don't be afraid, push it and hold it firm for 2 seconds. The starter should spin.

As stated, your switch isn't wired as you show. A switch needs to close to actuate the circuit. Your switch is wired in parallel to the original truck wiring.

Here's a quick sketch showing the path you need to follow.
The red is how your pushbutton switch is wired, although it doesn't seem to be attached to your starter like I show. Do you have a picture of your switch and how it's wired?

@blkprj80 I'd like to answer your question about how the button is wired. One wire from the button is spliced into the thinner black wire which connects to the starter with a blade connector. That's the negative terminal of the starter correct? The second wire from the button goes off into dark and tight places of unknown destination, but ends up grounded (confirmed with a multimeter), so that when the button is pressed, it momentarily grounds the negative starter terminal and completes the circuit to energize the starter. You are correct that the button is wired in parallel to the stock circuit, otherwise turning the key would never start the truck unless the button is simultaneously pressed. Not to muddy the waters but having said that, shouldn't your red (+) be a (-) ?

 

[jonheld]

The smaller blade connector is the starter logic from the ignition key. Terminal 1B in the diagram.
Ground for logic and starter motor are through the case of the starter. That gets bolted to the bell housing. There is no "ground wire" for the starter.

 

[jonheld]

Without the factory service manuals, you are blindfolded in a dark room.

I am also one who believes in fixing problems, not bypassing them.
The starter circuit is pretty simple and straightforward.

 

[CaliColin]

The smaller blade connector is the starter logic from the ignition key. Terminal 1B in the diagram.
Ground for logic and starter motor are through the case of the starter. That gets bolted to the bell housing. There is no "ground wire" for the starter.

Ohhh!! @jonheld A light bulb just lit up over my head with this statement! It’s like a cloud of fog just lifted. The starter is grounded thru its mount onto the bell housing. I thought the blade connector was the ground wire and thinking.. this thing is way too small to be carrying so much current. I believe I have my way forward now, and the diagram that @blkprj80 also finally makes sense. I know.. an fsm is in my future.