I am trying to use stock speedometer and tach on 89 TA with 98 ls1 computer. What is the best way to hook it up? I thought that i can feed the new vss signal from the new computer directly to stock speedometer but don't know where to find the wire going to the speedometer. The trans currently used is 4l60e. Also i found some info on needing to put a resistor between the new signal to original tach but not sure if i need to do that or tune can fix the tach signal.


EDIT:
update if anybody is searching:the tach as in the thread mentioned i had to add the resistor inline from a 12v source to the tach wire and also had to adjust the tach output to 3 in the computer using hp tuners. Spedo also just hooked directly from the 98 ls1 computer(c220 G) to where the output of the buffer box used to be. Both work fine except the stock tach redline starts a bit too early for ls1.

 

You can hooke the speedo wire from the LS1 PCM to where the buffer box is located behind the passenger side of the dash, it's a yellow box that is next to the cruise control. Since they changed some of the wiring color from year to year you would need a wiring diagram of the '89 dash harness to find out which color it was. The one on my '87 is green/black.

The tach you can have tuned for it to work right without adding any type of resistor.

 

The resistor mod is necessary on the tach if you have everything wired correctly but it's still not moving. There may be a place within the ecm to boost the power to this wire, but I went with the resistor and mine is working. My speedo wire was also green/black.

 

thanks for info, i will give it a try and see if i can get at least the spedo working first. Also apperently either my alternator is not turning on or is bad so i have to double check my wiring there

 

I got the spedo working and verified that it is working correctly but tach is a no go. It jumps about 500 rpms while idling but goes to zero as soon as rpms pick up. Is that a sign of needing a resistor mod or i need to supply extra power to it?

 

Yes you'll need a resistor, cannot remember what type. But mine has the same issue, it refuses to shwow rpm and and randomly jumps around with revs lol

 

Tach fix
http://www.ls1tech.com/forums/conver...t-correct.html

Info on the speedo
https://www.thirdgen.org/forums/ltx-...formation.html

If you hook the PCM speedo output to the stock place in the C207 then the splices at the buffer box will be all you need. I think for 89, Pin K is the speedo wire to the buffer