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Thread: Dash Wiring

  1. #1
    Senior Member Don's Avatar
    Join Date
    Oct 2002
    Victoria, BC Canada

    Dash Wiring


    I am getting back into the interior of the car this week and I am looking at finishing up the dash wiring for my aftermarket gauges.

    I have 2 main questions for all of you that have already done the swap from a stock Fiero dash to aftermarket.

    I am using Autometer gauges and all of the wiring for oil, temp, battery, idiot lights etc. is going to be OK but I am not quite sure about what to do with the electronic speedo and tach.

    I know on the stock Fiero, the speedo goes through the ECM and then up to the dash gauge and the tach does the same thing.

    With an aftermarket speedo I bought a GM sending unit as well. Will this be able to plug into the trans mount and I just connect the stock wires up to it or do I have to build an interface between the sending unit, ECM and speedo?

    Also, that same question would be for the tach. Can I just plug in the appropriate wires in the dash harness into the tach wires and have it read correctly?

    I had read over on Pennocks that an interface board was needed to use aftermarket gauges in the Fiero.

    308 Ferrari replica
    Prova Countach 5000QV

  2. #2
    Moderator FunnyWheels's Avatar
    Join Date
    Nov 2002
    Tampa, FL

    Re: Dash Wiring

    Don: I forgot to mention the Speedometer information to you on your email. The old Fiero sending unit will not work with aftermarket gauges. It has to do with the sensor in the transaxle. I had to split the cases and install the new style pulse unit. It produces 24,000 pulses per mile rather the 4,000. You might be able to figure out a way to build a board but I was not successful doing so and took another route.

    VDO Speedometer Set Up on my 355 replica

    Pin #1
    Pin #2 + side of Transmission Sensor (new wire)
    Pin #3 on the VDO hooks to Fiero “P” Black/White (Ground) Also – side of Transmission Sensor
    Pin #4 on the VDO hooks to “V” Brown (12 Volt Input-Keyed)
    Pin #5
    Pin # 6 Jumper to “8”
    Pin #7
    Pin # 8 Jumper to “6”

    One of the pulse leads from the new wire on the VSS goes to the VDO Pin #2, the other side of the VSS wire goes to Pin #3 and to ground

    If you want to test the Hall Effect Sender, try this:

    Turn ignition key “ON”. Put red lead of voltmeter to term #2 and black lead to term #3. You should have between 5-12volts DC.

    With the key “ON”, leave the black lead on term #3 and put the red lead on term #8. Remove the sender from the transmission. Rotate the square drive shaft in the sender very slowly with your fingers. You should see the voltmeter pulse from 0-4 volts DC. (0-4-0-4-0)

    If it pulses, the sender is working properly. If the voltmeter stays a constant 5 volts DC, the sender is defective. I found that the pulse per mile ratio will not work with the newer units.

    If you're not confused, you're not paying attention.

  3. #3
    Senior Member Don's Avatar
    Join Date
    Oct 2002
    Victoria, BC Canada

    Re: Dash Wiring

    Thanks very much Dave. I was wondering if I was going to have to split the case for the aftermarket sender as I have seen that done by members on Pennocks.

    Before I go that route, I may talk to JScott1 on Pennocks as he had posted over there that he builds conversion boards to do the aftermarket gauges with stock ECM and engine sensors.

    I had emailed him before but wasn't ready for that yet.

    Since I am also doing a 3.4 DOHC conversion as well, I may talk to the fellow I am getting to do the harness for me about the aftermarket gauges included in the engine sensor and PCM programming he will be doing for me.

    Thanks again.
    308 Ferrari replica
    Prova Countach 5000QV

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