Park/Neutral switch function??

[Wallybanger]

Anyone intimately familial with how the Park/Neutral switch on the transmission functions?



I am going to wire up a turbo timer/warmup circuit with my EGT gauge but I want it wired so that if anyone smashes a window and jumps in the engine will quit as soon as they put it in drive.



Just wondering when the circuit is open/closed and whether it's powered or grounded.



I could probably get out there and screw around with my volt metre but it would be nice to do up a little wiring diagram before I start cutting things.



Also, any oppinions as to where the best place would be to take ignition ON power and power from the dimmer for the dash lights?

 

[JDancoe]

Park/Neutral Switch Function

Actually the switch is open and closed and is powered and grounded.

I/m assuming you have an A/T, as the M/T trucks don't have a neutral safety switch.

The switch connector has three terminals and wires.

The White wire is a power wire from the #3 (Back-up light) fuse.



The Violet/Black wire is the output to the back-up lights and is hot when the switch is closed. (in reverse)

The Brown/Yellow wire is the ground circuit from the Starter Relay. When the switch/circuit is open there is no ground for the relay, hence, no start.

When the switch is closed (in park or neutral) the circuit & relay is grounded thru the switch - to the trans. case.

Hope this helps.



Some more advice: The Factory Service Manual has excellent wiring diagrams, and personally, I would hate to try to diagnose or modify my electrical system without one.

I have both the paper edition, which I bought when I bought my truck in 1992, and the CD version which I purchased recently from Geno's. The feature I like best about the CD is the ability to print out the page I need, put it in a sheet saver, and have it handy where I'm working. Also, you can enlarge the print copy if, like me, your eyes are old and tired.



Good Luck, Jack Dancoe

 

[Wallybanger]

Awesome, thanks so much, that is EXACTLY what I wanted to hear And yes, it is the auto transmission.

I have the FSM but I couldn't find anything on the function of the switch. I think all I had to go on was sheet 10 of the wiring diagrams and it just has a lame switch diagram that, in no way, relates to the transmission gear position.

Where did you find that info?

Cheers,

 

[JDancoe]

Park/Neutral Switch Fnction

In my FSM, page 8W-50, Sheet AD-7 shows the the connector, switch, and the starter relay, and related wiring color codes.

Jack Dancoe

 

[RSchwarzli]

Interesting idea... .

I assume you want to leave your truck running an then have this lock them out if they start driving?

If its when the truck is parked, better (read easier) to add a hidden switch to prevent starting.

 

[JDancoe]

Some thoughts on theft protection.
A switch to disable the starter function would certainly be the quickest & easiest way to go. But if the thief has time, and some know-how, he could jumper the starter.

Some years ago a friend of mine devised a system which incorporated a fuse in the ignition feed circuit, and a switch downstream of the fuse, with a circuit to ground when the switch was closed ("On"). If the car was started with the switch "On", the fuse would blow, and interrupt the ignition circuit, and the car couldn't be started until the fuse was replaced. It would crank, but not run. Something similar could be done with the fuel solenoid circuit on our diesels.

The elegant part of Wallybanger's idea is that the truck would run when started but die when put in gear. I'm thinking a thief would get frustrated after 2 or three tries and give up.

Jack Dancoe

 

[Wallybanger]

In my FSM, page 8W-50, Sheet AD-7 shows the the connector, switch, and the starter relay, and related wiring color codes.
Jack Dancoe

Cool, thanks. I'll take a look.

Interesting idea... .

I assume you want to leave your truck running an then have this lock them out if they start driving?

If its when the truck is parked, better (read easier) to add a hidden switch to prevent starting.

Yep, it's so I can lock the truck and leave it running to warm up or so I can lock the truck and let the turbo timer cool it down. Then if anyone breaks in and tries to put it in D or R the engine will die.

Yeah, I'm gonna put in a hidden switch too.

Some thoughts on theft protection.
A switch to disable the starter function would certainly be the quickest & easiest way to go. But if the thief has time, and some know-how, he could jumper the starter.

Some years ago a friend of mine devised a system which incorporated a fuse in the ignition feed circuit, and a switch downstream of the fuse, with a circuit to ground when the switch was closed ("On"). If the car was started with the switch "On", the fuse would blow, and interrupt the ignition circuit, and the car couldn't be started until the fuse was replaced. It would crank, but not run. Something similar could be done with the fuel solenoid circuit on our diesels.

The elegant part of Wallybanger's idea is that the truck would run when started but die when put in gear. I'm thinking a thief would get frustrated after 2 or three tries and give up.

Jack Dancoe

Yep, I probably won't even bother doing anything with the starter because they won't have the key. The whole system will control the fuel solenoid.

Because the gear position switch is just a path to ground I can control damn near anything with it It's not really a novel idea... . every car with a remote starter has a similar circuit.

 

[Bob4x4]

Cool, thanks. I'll take a look.



Yep, it's so I can lock the truck and leave it running to warm up or so I can lock the truck and let the turbo timer cool it down. Then if anyone breaks in and tries to put it in D or R the engine will die.



Yeah, I'm gonna put in a hidden switch too.



Yep, I probably won't even bother doing anything with the starter because they won't have the key. The whole system will control the fuel solenoid.



Because the gear position switch is just a path to ground I can control damn near anything with it It's not really a novel idea... . every car with a remote starter has a similar circuit.

Be sure to use relays... . the ns switch will fail with too much amperage

 

[DVolk]

Agood shot gun trap makes theves move on or a wire hooked to a coil to were they get shocked when useing the switch or the gear shift

 

[HHhuntitall]

Shotguns make a mess.....

 

[Wallybanger]

Be sure to use relays... . the ns switch will fail with too much amperage

Oh, I will Will probably havbe an bank of them under the dash that are easy to get to.

 

[DVolk]

maybe a big snake , but then i hate snakes

 

[ZedMikey]

How about a big, electric snake with a shotgun?

 

[Wallybanger]

You guys have too much time on your hands. lol

 

[DVolk]

may be LOL !!!!!!!!!!!!!!