I know the speed density does not use a buffer box but the harness that i am converting did. On my pin outs it lists a high and low for the VSS coming into the computer how do i know which is the high and which is the low wire? None of the wiring digrams that i looked at for the harnes listesd a difference

 

Not sure what you are actually doing, but the magnetic VSS has a neg. pole and a pos. pole. You can hook it up either way.
J

 

i am converting a harness to run on the 730 ECM. The harness orignaly had a VSS Buffer box. I was wonder how you go about plugging the wires into the 730 ECM to make it work

 

The 730 ECM will work with either an optical or magnetic VSS. It requires a PROM change and a different pins on the 730 ECM. So the choice is yours and it only depends on what the new vehicle has for a VSS.
I use a 730 ECM with an optical VSS and it works fine. The 165 ECMs need the buffer box because they can't take the magnetic VSS inputs directly. The buffer box turns the magnetic VSS signal into the same type of signal that the optical VSS outputs.
This has been covered many times on this board. A search will give you the correct pin swap and PROM change.

J

 

I am putting this set up in a 74 Blazer. I planed on using the after market spped sensor that ties in to the cable driven system so that i dont have to have a custom toner ring made for my transfer case.

 

That would be a magnetic VSS with two wires coming out of it. So you want to connect to the normal 730 pins and do not need to change the code. The 730 $8D code is set up for magnetic from the factory.

J

 

ok does it matter with this setup which wire goes where?

 

It does not matter which of the two wires goes where but you have to connect them both to both of the VSS pins on the computer. That is, don't connect them to the O2 and Knock sensor pins or something like that.

J

 

Do you know the outputs of your aftermarket vss?

730 ECM inputs vss bufer box inputs
VSS low BB9 = purple wire 401 pin c
VSS high BB10 = yellow wire 400 pin a

or this way with code change
730 ECM inputs vss buffer box output
Buffered BC6 = brown wire 437 pin f

Hope this helps, good luck with your project

Oh buy the way get a guage cluster out of a 87 p/u they have vss built in. Some other years also like88, 89, 90, 91 crewcabs, blazer and suburbans, maybe a few previous years also, its been a while ( ten years) since I did a swap into a truck like yours.

 

The clusters that have the VSS built in what type of vss were they? are they the types that would plug right into the 730 or would i have to change some things around?

 

I use a cluster with built in VSS. All of them are optical. The 730 ECM optical input is pin C6 (from memory). The $8D code will need a PROM change if you use the optical sensor. A quick search of the board with give you the exact values to change.