According to the Fox EFI wirning diagrams I have, the manual transmission Mustangs used a clutch switch and a neutral switch one of which had to be closed to allow start and also send a start signal to the PCM which, I presume, told the pcm to use a particular scenario.  I think the T5 switch is similar to the AOD switch which is a screw-in switch with two sets of contacts.  It is driven by the shift rails and provides neutral safety and back-up light functions.
 

Apparently, the neutral safety switch that comes with the TKO can't handle the continuous 12v Tremec says you need to install the relay.  

According to the diagrams using relays the only wire i would need to run down to the neutral switch is a ground so when i run my back up light and electric speedo wires I'll run an extra black/ground in case i decide to install later.  I would install the relay under the dash somewhere.



 

My car was originally a manual tranny car, so I saw no need for a neutral safety switch on my TKO600.  I know how to drive it without starting it while in gear.  I instinctively depress the clutch pedal when starting, even if I know the tranny is in neutral.  No need to idiot proof it.  Just don't let idiots drive it.

I think every other car should have an interlock just to protect MY car! Remember, the idiot is usually in the other car.

Raymond_B wrote:

Hmmm I thought the neutral switch only carried current to the small terminal of the solenoid when cranking? Why would it be 12v continuous?

Raymond – you are correct, the start circuit is only energized with the ignition switch is in the ‘start’ position.   The relay coil would need to be energized by the ignition switch being in the ‘start’ position.  The relay ‘normally open’ contact would need to be in series the ignition start switch and the neutral switch contact, then continue to the ‘S’ terminal on the starter solenoid.

 

BobE wrote:

I have a T5, but did not connect the neutral start switch ... although it is probably a good idea as I've heard of people starting the car from outside the car without realizing it was in gear, and the car took off, and went into something. 
I also do not think you'd need a relay. 

The switch has to be on for the engine to start.  There must be more to it than just pushing the car from outside with it in gear.
 

6sally6 wrote:

I think this will be filed under......"mods to do when I'm bored and already modded everything category!
I gotta couple of thangs already in that file.

I'm the sorta guy that takes the guard off of the grinder because I enjoy a lil element of danger.
One thing I like about my Mustang is...you can push-start it..if ya wanna.
It may be why I like to drive it around with open headers...cause ya ain't 'spose to.
Enjoy 'manual roll-down windows'....might be a control thang....I don't know!
If they didn't stink so bad... I might take-up smoking again.. liv'in on the edge don't cha know.
AC in a hot rod?!! Not...(besides AC makes my joints ache)

6sally6

I enjoy the A/C even with the windows down got use to riding around like that in Police car and like that with heat on in winter cant hear or see as good with windows up......Hard to hear a crime when BORG was barking too.
 

The T5 in Foxbody Mustangs have 2 switches built into the Clutch Pedal Switch (CPS) “clutch interlock”:

One requires switch to be closed for start circuit.

Second requires switch to be closed for ECM diagnostic testing Key On Engine Run (KOER).


There are 2 separate switches on the T5 transmission.

One is the Neutral Sensing Switch (NSS) for the ECM diagnostic testing KOER.

Second switch is for the backup lights.

The NSS is closed when transmission is in neutral…non gear position.

I don’t know how much current can be run through the NSS without damage.
It was originally for the ECM diagnostics only.

I don’t have a clutch pedal interlock switch on my T5.

The 12v is not continuous, however the inductive kickback that the starter coil sends back through the transmission switch is probably what is causing failures. Relay required due to “unknown failures”.

Last edited by Nos681 (1/19/2023 11:12 AM)

There are 3 locations on Foxbody.

2 switch combo above clutch pedal

and 2 separate switches on transmission.

Keep in mind the wiring differences between auto/manual factory HEGO harnesses.  Don’t want to fry ECM.
There is a short jumper that is routed to a different pin location that will feed 12 volts and burn up a trace on ECM.

Just looked at Rock Auto, same switch on 92.

Last edited by Nos681 (1/19/2023 5:58 PM)

Right Dan...looks to me like the Automatic (A9P) gets a 12V  signal from Ignition Start to pin 30 and the Manual trans (A9L) gets a Signal Return to pin 30 supervised by one of the set of contacts on that upper switch.  Hence my previous post.  Do the other contacts on that switch supervise the start circuit through a relay?  That's what it looks like to me.

Last edited by Bullet Bob (1/20/2023 8:36 AM)

Bob squared… (edit: if you click on the drawings they will  open and be clear(er.)










I have pins 30 & 46 located close to my diagnostic connector.
I have the A9L (manual transmission) ECM, 12 volts should NOT be applied to these wires for this ECM.
Eventually, these will be connected to my Neutral Sensing Switch (NSS) on the transmission…contact closed when in neutral.

I have to jumper these in order to perform KOER tests.
Code 67 will indicate this circuit open.

On the (manual transmission) 92, the 12 volt starting circuit is completely separated by the placement of 1 little jumper wire in a connector.  If jumper is wrong position, it could/very likely damage the A9L.
Ingenious way to save a buck, but can cause damage if unknown.

This jumper is located on the HEGO wire harness (O2 sensors and oil level low).
BTW, I deleted the oil pan switch for the front sump pan has no provision and mine was leaking through the switch.,,another wonderful idea…one more thing to break.

Notice my jumper was diagonal on stock factory 92 Mustang (manual transmission).
It was different than horizontal or vertical arrangement information I found.
It’s easy enough to relocate the jumper in the connector.
I used a different donor HEGO harness, and made it match my factory manual HEGO harness.

Hopefully I was able to answer your questions…kinda long winded.
Just don’t want someone to damage their ECM.

Last edited by Nos681 (1/21/2023 1:02 AM)

The 2 separate transmission switches have only 2 terminals each.

The clutch interlock switch has 4 terminals with 2 separate switches together.

Just want to clarify.