tbi harness help

[BIGWORM76]

Im working on my harness for my 76 scottsdale ( donor 90 1500 4x4) ive been removing all the uneeded wires and connectors and im down to a few last questions ?

The fuel pump relay has a red wire with a white stripe my book says its a fuel pump prime how and where do i hook it to ?

The transfer case is a np241 has a purple wire with white stripe and a solid yellow wire together on a plug are these vss wires and if so do they get re wired to the brown vss wire ( pin a A10 on the pcm) or are they something else ?

pcm pin # C9 is a purple wire book says its a crank wire ? is it needed where does it go ?

pcm pin #B10 is a orange wire with a black stripe book says park neutral switch do i need to hook this to anything ?

Thanks in advance for the help !!!

[one92rs]

not sure of the other wires but the red wire with a white stripe for fuel pump prime will hang loose. it is a test for the pump system.

[EagleMark]

The fuel pump relay has a red wire with a white stripe my book says its a fuel pump prime how and where do i hook it to ?

Nothing, it's to hook up 12 volt power to test or prime.

The transfer case is a np241 has a purple wire with white stripe and a solid yellow wire together on a plug are these vss wires and if so do they get re wired to the brown vss wire ( pin a A10 on the pcm) or are they something else ?

Pretty sure that is VSS twisted pair.

pcm pin # C9 is a purple wire book says its a crank wire ? is it needed where does it go ?

Goes to the solenoid terminal that is hot when in crank.

pcm pin #B10 is a orange wire with a black stripe book says park neutral switch do i need to hook this to anything ?

You can wire it into shifter, grounded is park, open is drive, or just leave it open but cold start and such is better with it.

[BIGWORM76]

the purple and yellow are twisted together, can they be tied into the brown vss wire from the pcm or do i still need to buy an aftermarket vss or if they can be tied in how ?

[bentrod]

the purple and yellow are twisted together, can they be tied into the brown vss wire from the pcm or do i still need to buy an aftermarket vss or if they can be tied in how ?

I went through this too and should probably make a PDF on the subject.

Anyway the '90 trucks really have 3 different VSS going on.

-the purple and yellow pair is for 120k pulse per mile (or PPM). This comes right from the trans or transfer case and goes to the DASH ONLY.
-the dash will convert them into 2 other signals; a 2k PPM for the ECM, and a 4k PPM for the cruse control.

Sadly, you can't just connect the VSS to the ECM here. The reluctor ring on your trans works like a little AC generator and makes a sine wave similar to that of your house 240vac wiring. The ECM is expecting at 0-5v TTL square wave. You need to use a '90ish dash OR make a device that converts the 120k AC PPM to 4k TTL PPM.

I was thinking about making such a conversion device and selling it, but I don't know if the demand is high enough to be worth it.

Also, this set up didn't last long. It was changed to this in '89 and I think by '92 they were sending raw VSS to the ECM, which did the conversion to TTL, then sent it to the dash/speed control. I know thats what they did for the LT1s anyway. I only own a '90 truck so don't hold me to those years.

[EagleMark]

There's a DRAC or VSSB under dash that does this.

[bentrod]

There's a DRAC or VSSB under dash that does this.

I have read about this separate DRAC device elsewhere on the internet, however my truck didn't have one. For my '90, the axle ratio conversion is accomplished all on the instrument panel. So I guess technically the truck has a DRAC device, but it's integrated into the I/P.

Maybe some got a separate device and some didn't? Also it may have been for a transition year thing or something?

[EagleMark]

Correct, some had the DRAC built into dash and some had an external box. In dash had a chip/resistor you could change that is no longer available. But the external has jumpers that can be changed or a Dip switch installed.

[bentrod]

Correct, some had the DRAC built into dash and some had an external box. In dash had a chip/resistor you could change that is no longer available. But the external has jumpers that can be changed or a Dip switch installed.

Welp, TIL! I wish I had signed up here sooner; I was pulling my hair out back during the swap.

The manual also goes over what is in the cal plug deally that goes into the back of the dash too. I cant remember off hand how it worked (it's just a crappy 8pin device). I'll be down this route again when I find a set of 3.21 gears for the 14bolt though.