Park/neutral switch

[Mastiff]

I'm going to be wiring a bunch more stuff to my ECM. I might not hook them all up right away, but I'm going to run the wires out so it'll be easy later: fan control, A/C control, fast idle, trans kickdown, VSS, IAT. So, should I think about wiring up a park/neutral? Does anyone bother with that? If so, how do you go about it?

[EagleMark]

Dave answered that in your other thread...
http://www.gearhead-efi.com/Fuel-Injection/showthread.php?629-VE-coming-out-way-over-100&p=6383&viewfull=1#post6383

I've done a micro switch for park on shifter linkage and not worried about neutral. So idle is good in park and IAC logic works when shifting into gear.

[dave w]

I used this schematic from Painless Wiring. I used a 6 amp diode from Radio Shack: (notice how Painless does not show part numbers)

6A, 50V Rectifier Diodes (4-Pack) Model: 276-1661 | Catalog #: 276-1661

The factory uses a crank fuse that is 3 amps, so I'm sure the 6 amp diode is more than up to the job.

dave w

EDIT: From the Painless Manual
60122
PARK/NEUTRAL RELAY
INSTALLATION INSTRUCTIONS
1. MOUNT THE RELAY IN A CONVENIENT LOCATION UNDER THE DASH NEAR
THE DRIVER SIDE.
2. DISCONNECT OR CUT THE START WIRE FROM THE IGNITION SWITCH, USING
THE YELLOW BUTT CONNECTOR SPLICE THE SHORTER PURPLE WIRE FROM
THE RELAY TO THE CUT PURPLE WIRE AT THE IGNITION SWITCH.
3. ROUTE THR PURPLE WIRE FROM THE RELAY TO THE “S” TERMINAL AT THE
STARTER SOLENOID. TERMINATE THE PURPLE WIRE WITH THE YELLOW
RING TERMINAL AND MOUNT THE PURPLE WIRE TO THE “S” TERMINAL.
IF THE PURPLE WIRE IS NOT LONG ENOUGH TO REACH THE STARTER
SOLENOID, USE THE YELLOW BUT CONNECTOR AND SPLICE THE PURPLE
WIRE FROM THE “S” TERMINAL AT THE STARTER SOLENOID TO THE PURPLE
WIRE FROM THE RELAY.
4. USING THE RED BUTT CONNECTOR SPLICE THE ORANGE/BLACK WIRE TO
THE ORANGE/BLACK WIRE AT THE ECM (COMPUTER).
5. ROUTE THE BLACK WIRE FROM THE RELAY TO THE NEUTRAL/SAFTEY
SWITCH AND CUT TO LENGTH. TERMINATE THE BLACK WIRE WITH THE RED
FEMALE SPADE TERMINAL AND CONNECT IT TO THE NEUTRAL/SAFTEY
SWITCH.
6. LOCATE A SOLID GROUNDING POINT NEAR THE NEUTRAL/SAFTEY SWITCH
AND ATTACH THE SUPPLIED GROUND WIRE. ROUTE THE BLACK WIRE TO
THE NEUTRAL/SAFTEY SWITCH AND CUT TO LENGTH. TERMINATE THE
BLACK WIRE WITH A RED FEMALE SPADE TERMINAL AND CONNECT IT TO
THE NEUTRAL/SAFTEY SWITCH.
7. TEST THE RELAY FOR PROPER OPERATION.
60122.doc 04/17/2002

[Mastiff]

That's great, thanks. I didn't think about the "only start in park" feature that could be taken advantage of. I can't say I quite understand why a whole new relay is required... I need to look at the factory schematic to see what changed. I would think you could just tap into the switch in the column and call it a day. I guess I'm not sure what the diode is protecting against either. They must think there is a danger of the relay trying to sink too much current into the ECM. But the ECM controls a number of things by pulling pins to ground and I don't think they all require diodes...

[Six_Shooter]

The relay is required, because the function of the column mounted switch is changing. Originally it would have simply been a switch for the start wire, now, you're trying to use it to control both the start wire and tell the ECM that the vehicle is in park. The start wire is a positive trigger, and is only energized while the key is turned forward, while the N/P trigger is a ground, and should be active whenever the gear selector is in park or nuetral. The use of the relay accomplishes both of these functions. The diode is there to prevent any back flow from the ECM that could allow the N/P relay from energizing when it is not supposed to.

[Mastiff]

Oh, so in the factory configuration the safety switch passes +12 to the starter when the key switch is engaged. That makes sense. There really isn't a way to use an open/ground switch to lock out the starter solenoid since it's grounded through the engine block.

I'm not sure if this is worth the trouble to hook up, but maybe I'll bring out the wire so I can do it some time if I'm bored.