I have a 99 F250SD 5.4 4r100 I have a no start, I can start the truck from the fender mounted solenoid/relay but I can’t start it from the ignition switch, looks like the previous owner bypassed the NSS but has failed over time, how exactly do I bypass the NSS?

 

The correct answer is you don't bypass it, you fix it correctly. It's called a neutral SAFETY switch for a reason.

 

I bet you work for osha don't you? Explain the reason behind a neutral safety switch, it’s pretty much useless.

 

No I don't work for OSHA, but I do understand that their purpose is to keep people from getting injured or killed. A neutral safety switch keeps the vehicle from being started while it's in gear, then unexpectedly lurching forward or back and running over adults, children, and pets.

 

This truck is a toy, just want to bypass it so I can have fun without spending 100$ on a harness and 100$ on a new switch

 

Why do you think it's the NSS? If the PO already bypassed the NSS, how has that bypass failed? You should just be able to trace the wires and redo whatever they did to get it running again, or If you can find a wiring schematic of that circuit you should be able to figure it out. Otherwise it's a different issue like a bad ignition switch, or something else. Have you tried to see if there's any codes that might show whats wrong?

You probably won't kill anyone, but a NSS isn't a bad thing to have just to stop accidental property damage. My old plow truck had the NSS bypassed for years. I was pretty good about checking to make sure it wasn't in gear but forgot a couple times. Worst one was when i reached in through the window to start it it lurched forward. It pushed the front wall of my old garage back 4" and bent the door tracks. Luckily i was able to shut it right down or it would've pushed that wall right in then taken out my 69 Impala. After that happened i installed a NSS and always double checked to make sure both the tranny and t case were in N before i worked on anything. That could've been very expensive. I had also bumped the starter from under the hood a couple times while it's in gear and I'm hanging off the front of the truck working on it. That's always fun, between having to hold on for your life and having all your tools, and the parts and hardware, on the fender and radiator go flying everywhere then having to hunt for it all.

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So you are wanting to bypass the NSS that is already bypassed? Or are you wanting to bypass the bypass? A little more clarity always helps.
If the PO did some cobble wiring to create a bypass, that would be where I would first look. Then the ignition switxh itself may be suspect.
NSS is not a bad thing to have, even on toys. However, on an old Jeep that I built, stick shift, I built a bypass that was kind of hidden, that would engage the starter, bypassing all nannies. But I still had the regular key ingnition that required stepping on the clutch, etc. before the starter would engage. The two worked independently of each other.

 

At this point I just want the wiring diagram for the neutral safety switch, I have a yellow and black wire that is cut and can’t find anything online about it and nothing in my Haynes manual

 

The Y/BK wire isn't part of the starter safety interlock, it's one of the four digital outputs from the DTR switch that tells the PCM what position the shift lever is in.

If all you want to do is to scab in a bypass of the safety interlock, run a wire from the small terminal on the starter relay to a cabin-mounted momentary contact switch whose other terminal is connected to a fused ALWAYS HOT battery source.

 

I THINK YOU GUYS JUST HELPED ME. I DID A CAB SWAP, AND MY TRUCK WOULDNT START, I BET MY TRANSMISSION ISNT IN PARK ALL THE WAY. THANK YOU.

 

so I just replaced the NSS, started a few times with the key, then it wouldn’t start, figured it may be a defective NSS just installed the new one and nothing still any ideas?