S10Wildside

I'm working with a carb to TPI swap in an 86 Silverado. I need a ground signal when the truck is in park or neutral. The ECM requires this.

Painless sells a kit that uses the Neutral Safety Switch. Here's their description:
You'll notice that it's simply a relay that switches ground to the ECM (orange/black wire). Looks like they've also got a diode in there.

I can't figure that out. I made this diagram yesterday to understand it, but the way I see it, the ECM would only see ground when the key is in crank and the selector switch is in Park or Neutral. I'm assuming the gear selector switch contains (or is) the neutral safety switch. The Helm manual has disappointed me with "Neutral Safety Switch" wiring...it doesn't seem to exist, however, the "Gear Selector Switch" is only going to let the engine start when the switch is in Park or Neutral.



Any ideas?

Vader

Yes, it appears with that diagram, the ECM is only going to get a "NEUTRAL" signal when the start switch is closed. You could rewire the entire apparatus so that the power routes through the safety switch before the ignition switch. However, this may be a problem since all the ignition switch current would have to pass through the safety switch, and that may kill the engine when the vehicle is placed in a gear other than PARK or NEUTRAL.

I'm working on it...

S10Wildside

Vader,

Check this out. Hours ago I found that GM has a ground signal on the 87-newer Neutral Safety switches. It's the single terminal on the right in the picture below.



I installed this today to find that this terminal only had ground in Park, not in Neutral. I'm really not overly concerned about this. Even Painless Wiring's installation manual suggest that the ORG/BLK wire has ground in Park...they don't mention Neutral. The older switches don't have this terminal on the right. However, the relplacement switch is the same as the 87 and newer switch.

Vader

They didn't include the entire circuit in their diagram. The cold start switch is also powered by the start wiring (if equipped with cold start). The GAUGES fuse is hot in the RUN, CRANK, and BULB TEST positions of the ignition switch, so the realy should operate whenever the ignition is on.

There is a diode drawn in the main starter solenoid power circuit from the ignition switch that may be necessary to prevent the indicator lamps and temperature gauge from being powered inadvertently. If this diode is necessary, it will need to have a PRV of at least 30V and should be able to safety pass a sustained 20A current. Don't cheap out on this one or you may get stranded.

I'm thinking this system should work. You'll need to use a fairly high impedance relay coil, at least 250 ohms. The relay should get adequate grounding through the starter solenoid winding (low impedance). The 150 ohm resistor and relay coil impedance should limit current so heating of the starter solenoid and cold start switch should be minimal.

Vader

Shee-ot!

All that dinking around with the circuit, and you solved it with a factory part.

S10Wildside

Honestly,

I found that switch hours before I posted the last reply.

Here's the details about the new switch...I wasn't what I expected to see. http://www.eficonnection.com/eficonn...lectronics.asp. (bottom of page)

fasttek

I realize this is an old post but thought someone could use this info in the future. I am installing a TPI system into a 67 GMC truck with a floor mounted B&M shifter connected to a 700R4 trans. The funny thing is I came up with the almost same exact solution before I saw this post or the Painless wiring diagram. I have a degree in electrical engineering so go figure.. The only difference between my setup and the Painless is my wire connected to terminal 86 on the relay is connected to my ignition wire and not the purple start wire. The ECU needs to know if you are in park or neutral when the car is running not just when it is cranking. So there is no way the Painless diagram would would work the way it is drawn. I didn't have a diode in my setup but it makes sense to prevent a surge and to keep the voltage level under 1 volt when grounded. The ECM recognises anything under 1 volt as the shifter is in park or neutral. I also added a 500 ohm resistor between the relay terminal 85 and the ECU to limit the current draw by the ECM as an extra precaution.

Hope this helps someone down the road.