[EddieP]

I'm just finishing up a TBI swap on my "new" 85 Blazer, but I've got 2 things left to do... hook up the park neutral switch and VSS wire from the ECM to the switch.

1. Does my '85 Blazer have the P/N switch already, or is it something I have to get at the junkyard? My blazer is a factory auto w/ cruise control.

2. Where is the park/neutral switch located? I know it's on the steering column somewhere, just not sure where exactly. What does it look like?

3. I've located the VSS buffer, and it has 3 wires - which wire do I need to spilce into for the VSS signal?

Thanks! I grounded the p/n switch wire from the ECM and started my truck for the 1st time with TBI - starts and idles great! Really pumped about getting it on the road.

 

[The_Raven]

The park/nuetral switch IS located on the steering column, it will be near the base of the column, near the firewall. You will most likely need one from a newer S-series that was EFI equipped, since I'm pretty sure the non EFI or CCC trucks did not have the park/nuetral wires, but just the starter wires. There are two other wires on the EFI or CCC equipped S-series, one is a ground that I believe is actually grounded through the ECM and the actuall park/nuetral signal.

The VSS that you located should be behind the gauge cluster, since you are saying that your truck all ready has one, this means you should also have crusie control, correct? I believe the 3 wire colours are Pink, Black, and Brown (it's been a whie since I looked at mine, and didn't work with my ECM anyway), the signal will be the Brown wire, the Pink is ignition and the Black will be ground.

 

[EddieP]

Thank Raven,

I've found the p/n switch at the base of the column - there are two pig tails pluged into it, and each pigtail has two wires (total of four wires going to p/n switch). I'll try and get a volt/ohm meter on it and figure out if it'll work. Does the EFI version have an extra connector on it?

Yes, it's a '85 with cruise control. So the carb VSS buffer didn't work for you? Is there a difference between the TBI and carb VSS buffer?

 

[The_Raven]

The 4 wires should be two large wires, a Yellow and a Purple, and then 2 smaller wires IIRC a Black/White and an Orange/Black, if so this will be your P/N wires for the ECM, They may actually be used for the cruise, mine is a manual tranny, and didn't have cruise when I bought it, but I have ripped apart a few there were autos.

I'm using a different ECM than you, I can gaurentee that, and that is why the VSS didn't work with my ECM. Also it depends on what year of S-series ECM you are using, I have read, but not verified that some of the later model S-series will require a different VSS than the cluster miunted VSS.

 

[EddieP]

The ECM came out of a '86, so hopefully the VSS should be fine.

I'll double check the wires on the P/N switch tomorrow, but I'm pretty sure the switch in there now has a few different colored wires than the EFI switch you are describing. I remember right, one of the pigtails has a solid blue and a solid green wire ... I *think* they went through the firewall and spliced into the TCC wiring. Maybe the P/N switch that's in my car now uses the extra wiring as a 4th gear switch for the TCC??? Hehe, looks like I'll probably head back out to the bone yard tomorrow and get the right switch.

 

[The_Raven]

Oh, duh *smacks self on forehead*, The green and blue wires are the reverse light wires. I forgot about those, probably because they are on the tranny in my truck, sorry about that. So yeah the EFI switch will have an extra plug. I don't know about direct compatibility in swapping them, but I can't see why not.

Yeah I can't really foresee any issues with the VSS and the ECM you are using.

The TCC (lockup) is controlled by the brake pedal and an output on your ECM. I don't remember if there was a relay triggered by the ECM or not, best to check the schematics here. With the carb it should be through a vacuum switch and the brake pedal.

 

[EddieP]

Ahh, that makes sense - you're a lifesaver!

Oh, duh *smacks self on forehead*, The green and blue wires are the reverse light wires. I forgot about those, probably because they are on the tranny in my truck, sorry about that. So yeah the EFI switch will have an extra plug. I don't know about direct compatibility in swapping them, but I can't see why not.

Yeah I can't really foresee any issues with the VSS and the ECM you are using.

The TCC (lockup) is controlled by the brake pedal and an output on your ECM. I don't remember if there was a relay triggered by the ECM or not, best to check the schematics here. With the carb it should be through a vacuum switch and the brake pedal.

 

[EddieP]

Update!

Went to the salvage yard today, and pulled the p/n switch from a 87 Blazer w/ 2.8 TBI... oddly enough, it only had two wiring plugs going to it. One was for the back up lights (blue/green wires), and the other was the ecm park/neutral signal (wires were black w/ white stripe, orange w/ black stripe).

I get back and compare the '87 P/N switch with my '85 switch... they are the same! Part number and all. In my '85, the spot where the ECM wiring plugs into has a plug with a black wire (ground) and a light blue wire with a black strip. I checked the light blue w/ back stripe wire and found it to be grounded in park and neutral, and open otherwise. I guess I can just splice the orange/black P/N signal wire from the ecm into the existing light blue/back wire that is already there?