I have just got a 88 formula w/350tpi.no motor or engine harness. I have a motor and harness from a 87 I think. Motor block may be a 88. The harness has no wires for the speedometer. This car has a vss box under dash and no mechanical cable coming through the fire wall. 140 cluster. Any in 88 come. MAchanial or they all impulse? Or I need a 88 engine harness.I got a TBI camaro with mechanical spedo

 

your bird has digital electronic speedo. not mechanical

 

The motor and matching wiring harness you already have from an 87 (you think) was probably from a 87 Camaro; and that's probably why there is no electric speedo wiring.

The 88 Formula has an Electric Speedo sending unit,....... regardless of the type of cluster.

 

Your right the harness was from a z28. There's a vss buffer box near the ecm mount area. If I want my spedo to work I need a firebird ecm? Or just run wires to the buffer?

 

Go to: https://www.thirdgen.org/technical-articles/ In the Miscellaneous Modifications is an article titled: Swapping an electric speedometer into your Firebird (off-site) This should help. Sorry, locked out of the article on my work computer.

 

OK. Sence my car already has the gauge cluster vss box and dash wires all I got a do is pull the wires from an electric type sender to the vss box.from what I gather from this, is the vss signal has nothing to do with the ecm its self.

 

These are from an 88 Firebird Shop Manual:





This is the C100 connector,... All you need to do is install the proper Electric sending unit ( with the correct Speedo Gear ), then find the proper plug with wiring and lead it up to the C100 connector however you desire. ( poke the 2 wires thru a small hole in the firewall, Ect.... ) You can cut/splice into the C100 wires under the dash and then the Cruise Control, ECM & Cluster will get the electric VSS signal as factory designed.

PINS/Wires = 'D4'/YELLOW and ' E4'/PURPLE

P.S. The Electric Speedo Sending Units for your car can be hard to find. Used from 84-89(?) on Berlinetta, Firebird and Vetts. Speedo gears are also electric and cable specific so be sure that you get the matching speedo 'DRIVE' gear too !

 

K. Thank. I will have to get on my home computer so I can print that info for my folder.