1227747 VSS wiring question

[EDZIP]

Getting ready to put together a stand alone (streetrod) harness for a TBI with 700R4 using the 747 ECM. Pin A10 indicates it is for "Speed Sensor Signal" (dash cluster?) but I don't see any ECM pins for the (2) VSS wires from the 700R4 speed sensor.

Is a DRAC required? -or- How are the (2) VSS wires tied into the 747 ECM? IN A NUTSHELL...how is the VSS tied into the ECM?

Used to working with the 730 ECM which has (2) specific pins for the VSS (4 pulse).

Thanks

Ed

[Six_Shooter]

Take a look at the diagrams on this site.

In most cases I have come across, the trucks use an optical sensor behind the cluster, at least up to about 1990 when a mechanical cluster is used.

With a non-mechanical speedo output trans, you will need a DRAC, or possibly grounding one wire and feeding the other to the ECM might work.

[EagleMark]

I've always used a DRAC for 700R4 trans. Even if speed is off because of tires and gears it's still close enough that you can adjust TCC lock up speed.

[EDZIP]

I've always used a DRAC for 700R4 trans. Even if speed is off because of tires and gears it's still close enough that you can adjust TCC lock up speed.

I'm sure you guys are aware of this adjustable "toggle switch" conversion:

http://www.tbichips.com/drac/

[Six_Shooter]

Yep, I believe that link is in the sticky at the top of this forum.

I've used that on several vehicles now.

[EDZIP]

[QUOTE=Six_Shooter;27769]Take a look at the diagrams on this site.

QUOTE]

Been all the site etc...the speed sensor on this 1990 truck harness has (2) wires (1) yellow and (1) purple w/white stripe. Reference on this site indicates that pin A10 "brown" VSS sensor signal to ECM.

Anyone have a diagram to indicate how the 700R4 two wire speed sensor is connected to the 747 ECM?

thanks

[Six_Shooter]

I don't know if the 700R4 came with a 4 PPR VSS, or if the 40 PPR VSS was the only electronic option. Either way, it sounds like you're going to need a DRAC.

[EDZIP]

I don't know if the 700R4 came with a 4 PPR VSS, or if the 40 PPR VSS was the only electronic option. Either way, it sounds like you're going to need a DRAC.

All of my 700R4 tranny's have 40 tooth reluctors

BUT I really need to know the wiring format..I can't locate any schematics for the 700R4 (40 pulse) with the 747 ECM....could also use a DRAC schematic.

Thanks
Ed

[EagleMark]

Maybe this will help?

[EDZIP]

Mark

Thanks - That clears up the VSS to DRAC to ECM

As mentioned the speed sensor on this 1990 truck harness has (2) wires (1) yellow and (1) purple w/white stripe.

Your diagram shows PPL-WHT and LT GRN-BLK from the VSS to the DRAC..."half of the colors match:-)"

Will the DRAC convert with "only" the (2) VSS wires, DRAC ground and brown A10 wire to the ECM (ie no cruise, abs etc)?

Thanks

[EagleMark]

Should? The Cruise and ABS are outputs... IIRC, been awhile since I played with these.

Where's the VSS coming from? Most trucks around that year have VSS in speedometer...

[Six_Shooter]

According to previous posts, this 700R4 has a magnetic reluctor in the trans with purple and yellow wires.

Just follow the pinout for the DRAC, ignore the actual wire colours at the DRAC, some wires change colour between where they leave the sensor/device, to when they reach the DRAC. Use the function of that pin instead.

[EDZIP]

Just follow the pinout for the DRAC, ignore the actual wire colours at the DRAC, some wires change colour between where they leave the sensor/device, to when they reach the DRAC. Use the function of that pin instead.

I should be good to go with all of these posts...would have been easier if I had just asked if the trans VSS output was directional like a diode instead of mentioning wire colors.

Ed

[EDZIP]

Attached is FYI, my local Chevy dealer had a wiring manual ST 372-92 EDD for a 92 Astro Van. Copied the DRAC info as jpgs (Have one PDF).. Split the page into right and left sides.

Wire # 437-.8 Brown goes to pin A10 on the 747 ecm.

[EDZIP]

Here is a PDF I just put together, it has the DRAC and VSS pin outs for a 1992 Chevy van, also inserted the VSS pin outs for a 1990 Chevy C/K pickup VSS. Should help wire up a 747 ECM with DRAC and VSS.

Hope it makes sense...

Ed