Swapping an electric speedometer into your Firebird
Swapping an electric speedometer head into a thirdgen Firebird is becoming popular, probably due to the operation of the electric unit being much smoother than a cable-driven one. Hooking it up to work properly (or at all) is the challenge many of us face. Hopefully this will help things to go along just a bit smoother.
Just a quick note beforehand:
This swap is from my own personal experience at installing the wiring harness and associated components from an 86 Firebird SE into an
89 Firebird Formula. The Formula was a theft-recovery, and had much of it's under-dash wiring hacked, including removal of the ECM. It is my understanding that only 86-92 Firebirds with guages had the electric units.......
If you plan to install one of these electric units into an 82-85 Firebird, the wiring to the cluster will need to be changed around a bit in order for things to work correctly
What you will need to accomplish this task:
Speedo head, or entire cluster if converting to gauges ( in which case you will also need to change the water temperature and oil pressure sending units).
The sending unit (VSS) from the transmission of the donor vehicle, along with appropriate gears to ensure your speedo reads correctly.
A new O-ring for the VSS.
The yellow (could be a different color) plastic box which is 'piggybacked' to the Firebird's ECM. A scanned image of the one I used is below.
The wire connectors from the VSS and the plastic box, along with as much wire as you can grab with them.
A plastic plug to fill the hole in the firewall from where you will remove the original cable.
Assorted wire connectors for splicing wires together, power hookups, grounds, etc.
How to install and hook up the unit
To remove the cluster
Disconnect the negative battery cable.
On models without cruise control, disconnect the speedometer cable strap at the power brake booster. On models with cruise, disconnect the cable at the cruise control transducer.
Remove the left and right side hush panels (the ones above your and your passenger's feet).
Remove the right and left side lower trim plates and attaching screws.
Remove the instrument cluster trim plate and attaching screws.
Remove the cluster attaching screws.
Pull the cluster out. Disconnect the speedometer cable and electrical connections.
Reach beneath the cable connection at the speedo head, push in on the cable retaining spring, and disconnect the cable from the speedo.
Remove the old cable from the dash and pull through to the engine compartment, and seal the hole with the plug.
To install the cluster
Wiring it up
|* These brown wires are normally hooked up to the ECM, and provide a 2000 Pulse Per Mile (PPM) signal to control speed-related items such as torque converter lockup, shift light, cruise control, and activation of the EGR system. This also provides a signal that can be used when hooking up a Global Positioning System (GPS) *|
Find a place to run the purple and yellow wires through to the transmission- the original route was through the plug on the passenger side just ahead of the door hinges. I ran mine underneath the shifter plate boot on the floor, and left enough slack for movement.
Find a place to later tie up the plastic box, and shorten (or lengthen) those wires as needed and splice together. Locate the wires previously hooked to the speedo head. Splice the one from the 'E' terminal to the black wire from the plastic box, then hook these to a ground screw or bolt. Take the one from the 'IG' terminal, splice it to the pink wire from the box, then run a wire from them to the fuse box and hook to a wire which has power only when the ignition key is in the 'RUN' and 'START' position. Connect the wire from the 'S' terminal to the green wire from the box. You can now tie up the plastic box and reinstall the hush panels.
On to the dirty work
Jack up the car and support it securely with jackstands (or use a lift if you are lucky enough). Have a pan of some sort ready to catch any transmission fluid that will drain from the transmission. Remove the cable from the existing sending unit on the tranny, then remove the sending unit itself. It is held on by a bolt and clamp (similiar to a distributor clamp and bolt). A 10mm wrench (a socket may not fit) will remove the bolt. The VSS unit installs the same way the mechanical one was removed. Then hook up the electrical plug, refill the transmission to the proper level, lower the car to the ground, hook up the negative battery cable, and you're ready to go.
This article has been researched
and written by Peter Hetherington, AKA Petes 84Z28 using
information and drawings obtained from Chiltons' 1982-1994 Pontiac Firebird repair manual.