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Electrical System Shut Down


V8path
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Have you tried disconnecting the ignition switch harness and testing the ignition switch for continuity scenarios (per FSM), as well as probing the live harness? Just to rule out the ignition switch...

 

Yeah, have done that and the ignition switch contacts seem pretty solid. However given its on the cusp of being 30 years old, I'm going to replace the ignition switch with a new aftermarket unit in the very near future.

 

Am going to do a bit more digging around the ignition circuit, as well as the wires to the starter/solenoid to eliminate or replace any visible potential problems in the next week or 2.

 

But its been over a week since disconnecting a few select alarm connections, and so far so good.

 

This has taken too much time away from the doubler build I started a few weeks ago.

Edited by V8path
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I just walked out to my truck, set the key to the run position, and jumpered between white/red (battery +) and black/yellow (easy because the plastic clamshell is broken). Hotwiring it like that made it crank. It did not start, however. Perhaps both the black/yellow and the black/green must be connected to + for the engine to start, so that a tweaker trying to hotwire your car will just sit there running the starter until the battery drains. In any case, if black/yellow was a ground, the bread tie I was using as a jumper would've burned up, or the fuse links would've popped, and either way the engine would not have turned over.

 

There is also no reason why the ignition switch would need a ground wire. It's just a switch on the + line. Connecting the + line straight to ground would just fry the fuse links. There's no antitheft chip-key bollocks in the lock cylinder that would require a ground.

 

So, why are you seeing voltage from white/red to black/yellow? Your test light is finding ground through the starter solenoid. A test light doesn't require much amperage to light up, so as far as it cares, the starter solenoid is just a wire between it and ground. The circuit goes dead when you're not in park or neutral because the inhibitor relay (which is between the ignition and the solenoid) breaks the circuit to prevent you from starting in gear. A test light will not tell you if it's getting a proper ground or if it's grounding through a load (a relay, light, solenoid, actuator, whatever).

 

(battery +) ------ (fuse links) ---white/red--- (switch) ---green/black--- (inhibitor) ------ (solenoid) ----- (ground)

 

That's the circuit. Fuse links are just wire, assuming they're not blown, so ignore them. The solenoid is just a coil of wire, and at the very small amperage it takes to light up the bulb in your tester, its resistance is negligible. Current goes straight through. Let's assume your inhibitor is not inhibiting. Mark that off too. Now you've got this:

 

(battery +) ----- (switch) ------ (ground)

 

Obviously that's not how the circuit is, but it's how it looks to the test light. If you test across any switch that's turned off, unless the load has a higher resistance than the little bulb in your test light or the circuitry in your voltmeter, you should see battery voltage or something close to it. (Turn the switch on with the tester across it and the meter should read zero or the test light should go out.)

 

It's not hard to misinterpret an electrical tester. A weak ground can also look perfectly good to a tester, but fail under load. Being an idiot helps too--I once unwrapped part of my wiring harness looking for a short circuit in my passenger's side high beam. It had me confused because it wasn't a dead short, but it was clearly leaking to ground somewhere. That somewhere turned out to be the little bulb in the cluster that tells me the high beams are on. :doh:

 

In any case, I'm pretty sure the starter circuit is not what was causing your issue. Yes, it wouldn't crank; but I'm guessing the inhibitor relay gets its power (through the switch in the shifter of course) from the RUN circuit, so if RUN is interrupted, the inhibitor inhibits and the starter doesn't work. The systems that still worked when you lost power are systems that don't receive power through the ignition switch. I would be less suspicious of the switch at this point and more of the run of wire and the fuse links through which it draws power--though of course the engine swap and security system may complicate matters.

 

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Hey Slartibartfast thanks for the input. I'll have to spend a bit of time and read your info, and try to understand how the circuit works.

 

As an FYI, I wasn't sure if this has any implication to helping identify the earlier problem, but here's a pic of the set of relays on the passenger fender. I was pretty surprised when I popped the cover and there was no inhibitor relay.

 

IMAG2709_zpsl4odjtby.jpg

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You're missing it because you said yours started as a MT truck, which doesn't utilize an inhibitor circuit. That probably means your current AT inhibitor switch is part of the equation that's causing the black/yellow to read as a ground when in P/N. I'd guess that if you look into that relay socket, you're missing some of the slide connectors that would be necessary if a relay was installed.

 

Take a look at this: http://www.nicoclub.com/service-manual?fsm=Pathfinder/1993_Pathfinder/Starting_charging_AT_wiring

 

If you lacked both inhibitor switch and relay, the B/Y may in fact be grounded. For an MT, B/Y led to the clutch interlock. Guessing some magic occurred during the engine/trans swap.

 

The FSM suggests there are two active leads when the ignition switch is turned to Start. B/Y is supposed to be one of them, but I can't determine from the FSM what the other is. It's the wire below the open/missing connector, and from a picture of the harness, it looks like it might be black/green. If that's true, perhaps it's the lead to your starter?

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You're missing it because you said yours started as a MT truck, which doesn't utilize an inhibitor circuit. That probably means your current AT inhibitor switch is part of the equation that's causing the black/yellow to read as a ground when in P/N. I'd guess that if you look into that relay socket, you're missing some of the slide connectors that would be necessary if a relay was installed.

 

Take a look at this: http://www.nicoclub.com/service-manual?fsm=Pathfinder/1993_Pathfinder/Starting_charging_AT_wiring

 

If you lacked both inhibitor switch and relay, the B/Y may in fact be grounded. For an MT, B/Y led to the clutch interlock. Guessing some magic occurred during the engine/trans swap.

 

The FSM suggests there are two active leads when the ignition switch is turned to Start. B/Y is supposed to be one of them, but I can't determine from the FSM what the other is. It's the wire below the open/missing connector, and from a picture of the harness, it looks like it might be black/green. If that's true, perhaps it's the lead to your starter?

 

Yup, this was originally a MT.

 

I have a grey relay on the passenger firewall, which I think is for the horn. I have 2 relays on the driver side mounted on the washer reservoir bracket. Any idea if these are inhibitor relay(s)?

 

IMAG2762_zps2lk2bn3f.jpg

 

Went back to check the black/yellow by putting the key into the “start” position and it lite up the test light, so there is 12v on the black/yellow AND on the black/green. The black/yellow is NOT GND.

 

The way it’s wired (with the engine swap) is the black/yellow goes from the ignition switch to the trans P/N, and from there to the starter solenoid.

 

Am still not 100% clear as to where the other end of the black/yellow wire goes to. As for the black/green, am not sure where that goes either, but that was not touched during the initial swap (15 plus years ago). It’s still intact.

 

Going back and correcting my earlier thoughts with the black/yellow wire and how it was wired, the (after market) alarm would have separated the “ignition to starter” circuit, however, this is where its gets interesting. The black yellow wire from the ignition ran to the trans console P/N switch, so there was no ignition power running thru the alarm module from the black/yellow (so no ignition or start power to cut off).

 

So now, most of the earlier misunderstandings re the leads on the ignition switch are corrected, but I'm still not definitively clear as to “how or what was shutting down the system”? Was it the alarm unit?

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So now, most of the earlier misunderstandings re the leads on the ignition switch are corrected, but I'm still not definitively clear as to “how or what was shutting down the system”? Was it the alarm unit?

 

Haha, so yeah, that's been the kicker about this entire black/yellow wire conversation...it's only relevant to starting the truck, not shutting it down. But, seemed like a "better to know, than not know...you know?" discussion.

 

I think the only way the alarm factors in is if it has some remote start and/or starter disable function, and it's malfunctioning. For remote starters, the alarm can purposefully shut down the vehicle...typical scenario is if the vehicle is started remotely and the alarm never senses the ON signal from the ignition switch within some timeframe, for instance. But, any malfunction here could shut the truck down.

 

Honestly, if you have no dependencies on the alarm (is it even wired into the door signals or control power locks or windows?) and aren't even sure what it does (or doesn't), I'd be removing it. One less failure point. Conversely, if you want a new old remote start alarm I've got one from a long time ago that I never installed, I'll sell it to you for a couple bucks :D.

 

Could also try a more brutish approach to recreate the problem: start the truck, and start smacking and tugging wire bundles, relays, harnesses, keys while in ignition, etc.

 

Can't help on identifying those relays, but the quickest test is to pull them up and see what wire is grounded, put a 12v source on the opposite contact (typically labelled "86") and see what turns off. If the wires are connected using slide terminals, make sure they still have firm contact.

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Haha, so yeah, that's been the kicker about this entire black/yellow wire conversation...it's only relevant to starting the truck, not shutting it down. But, seemed like a "better to know, than not know...you know?" discussion.

 

I think the only way the alarm factors in is if it has some remote start and/or starter disable function, and it's malfunctioning. For remote starters, the alarm can purposefully shut down the vehicle...typical scenario is if the vehicle is started remotely and the alarm never senses the ON signal from the ignition switch within some timeframe, for instance. But, any malfunction here could shut the truck down.

 

Honestly, if you have no dependencies on the alarm (is it even wired into the door signals or control power locks or windows?) and aren't even sure what it does (or doesn't), I'd be removing it. One less failure point. Conversely, if you want a new old remote start alarm I've got one from a long time ago that I never installed, I'll sell it to you for a couple bucks :D.

 

Could also try a more brutish approach to recreate the problem: start the truck, and start smacking and tugging wire bundles, relays, harnesses, keys while in ignition, etc.

 

Can't help on identifying those relays, but the quickest test is to pull them up and see what wire is grounded, put a 12v source on the opposite contact (typically labelled "86") and see what turns off. If the wires are connected using slide terminals, make sure they still have firm contact.

 

I have cut or disconnected any wires from the alarm module that were tapped into the black/yellow (run) wire, and the "valet" switch wire was also cut from the system. All that's left for the alarm module functions is the lock/unlock and the chirp/lights to register the lock/unlock. Anything to do with the ignition etc has been disconnected or disabled.

 

Its been 10 days and have not had a system shutdown incident since the above alarm wires/function have been cut or disabled.

 

Re the 2 blue relays (and thanks to Slartibarfast for the info), on a 4WD MT model, one of them is the interlock emergency relay and the 2nd is suppose to be a Park/Neutral relay for the AT model (which mine is NOT). Not sure why there's 2 relays there given mine is a MT.

 

What is the function of the interlock emergency relay?

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  • 2 weeks later...

Ever since cutting certain wires and disabling everything but the lock/unlock functions on the alarm module, there's been no issue with the the electrical system, but I'd still like to know what the interlock emergency relay function is?

 

Anyone know for sure?

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I think it's for the temporary clutch override so that you can start the truck without depressing the clutch (like if needing to start the truck on a steep incline). Surely a remnant from when the truck was MT.

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I think it's for the temporary clutch override so that you can start the truck without depressing the clutch (like if needing to start the truck on a steep incline). Surely a remnant from when the truck was MT.

 

As long as it doesn't affect starting/running etc. I can leave things for now.

 

I'm planning to clean up some of the added (or no longer needed) wiring from the swap in the spring/summer. Picked up a fuse block harness from an LT1 that will be the second fuse block (and plans for a dual battery set up) for things like the dual electric fans (which manual on/off overrides), off road lighting, fog lights, DRL, etc etc.

 

Am also swapping in a coil on plug conversion onto the LT1 in the coming months, so will make sure the new PCM and main ignition power sources come from the secondary fuse block. This should eliminate any issues from the OEM Nissan system.

 

Want to make sure this thing is reliable, as am playing around with the idea of swapping in a TPI intake onto the LT1 (for gobs of low to mid range torque) and cam shaft upgrade when I'm into the coil on plug conversion. A buddy did this on his LT1 and dyno'd at mid 400HP and mid 400 ft lbs of torque.

 

Hoping to have a very special Pathy by the end of next summer.

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