So, since my speedo, odo, and trip meter don't work, nor will my cruise engage, and I get code 24, I'm assuming my VSS has gone the way of Pontiac itself.

From my rudimentary understanding, the VSS on a 2.8L 4 Speed is 4,000ppm. If I install a GPS speedo sender that produces 4,000ppm and wire it to my VSS wiring, would that operate my left hand side of my cluster (aforementioned gauge/meters) as well as send speedo data to my ECM?

GM 25007268 is interchangeable with 10457264 - ~$100 on eBay
https://www.ebay.com/itm/135049000454?

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Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

That's VERY good to know! However, it's the same price as the GPS unit from Summit (within $10)

I believe proper signal inputs from the VSS are important for best engine and and transmission operation. If you try to substitute something for the VSS the non- linearity of both the variable frequency and voltage outputs may or may not coincide with those of the VSS. I am not saying that it cannot be done just that it might prove difficult to achieve proper operation. .

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

[This message has been edited by Dennis LaGrua (edited 04-18-2025).]

The Fiero speedo works off of 4000 ppm analog. (sine wave)

The signal from the GPS is most likely digital. (square wave)

gmtuners.com has a wiring diagram to convert the square wave (digital) signal to sine wave (analog).

Your speedometer can run on the digital, but it will eventually cause damage to the speedo board.
The speedo board feeds a 2000 ppm signal to the ECU for calculation purposes.

I would recommend building the digital to analog conversion circuit if you use the GPS signal.