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Auto to manual transmission swap


Whippoorwill71
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I have a 1996 or a 11/95 manf. date  RECEIPT Vehicle 

4x4se auto trans

.  And a 1997 or 11/96 manf. date  DONOR

4x4se standard trans

ALL mechanical portion of the swap DONE

ecu swapped 

im an ok mechanic but electrical is not my strong suit

 

 

STILL NO START

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Sounds like an inhibitor issue, then. The inhibitor is meant to stop you from starting the car and having it bump a parked car, run over your foot, or roll backwards off of a four-post lift and out the door. Autos won't start unless they're in park or neutral, manuals won't start unless the clutch is pushed in. The switch for your inhibitor was on the auto trans you got rid of, so you need to rewire it to the switch on your new pedal box. You can see diagrams of both systems here (scroll down to page 31).

 

The inhibitor system has a switch and a relay. The switch is easy enough to understand, the relay is just a switch that connects the starter to the ignition switch when power is applied to the coil inside. In the auto trans rigs, what you have (in terms of the wiring anyway), the inhibitor relay coil has constant ground to one side, and + is switched to the other by the inhibitor switch (on the trans). So if it's in park or neutral, current flows through the relay coil, the contacts come together, and the wire from the starter switch is connected to the starter motor. In manual rigs, what you're trying to replicate, the coil has constant + to one side and ground is switched to the other by the clutch switch. Clutch in, relay energized, switch and starter connected.

I see a couple of options to get the inhibitor working with your swap. You could take the harness that used to go to the switch on the AT (white/red stripe and yellow), extend it back into the cab, and connect those to the two pins on the clutch switch. This wouldn't perfectly replicate the stock circuit, but the relay wouldn't care. With a little staring at the wiring diagrams in the manual, you could probably work out where those two inhibitor switch wires come from under the dash and save yourself some screwing around to bring them back in from underneath. The other option is to join the old inhibitor wires together wherever it's convenient, then cut the ground wire from the relay (there are two black wires, unhelpfully, and you only want the one for the relay coil--its the one on pin 2, if that helps) and run that to the clutch switch, then connect other pin of the clutch switch to any convenient body ground. This is closer to the original MT setup (not that the relay cares) and might save you some screwing around with the harness to the old switch, though I don't know if the ground on the relay would be any easier to bring in (didn't check where it's located). I'd probably go for the first option, especially if I could find those white/red stripe and yellow wires under the dash.
 

At this point you may be thinking it would be easier to just bypass the inhibitor and be done with it. Unfortunately, the computer monitors this circuit, and will throw a P0705 code if it doesn't see the signal changing when expected (diagram on EC-214). There's also the obvious safety issue--even if you always remember to push the clutch/take it out of gear before starting it, your mechanic/valet/idiot friend or family member may not. That's not to say I didn't do exactly that on my dad's old F150 rather than replace the clutch switch when it wore out. For testing purposes... temporarily... you could just jumper those old AT inhibitor switch wires together to get it running, then come back and fix it the rest of the way when you get tired of looking at the check engine light.

Hope this makes sense. Good luck!

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