1991 Testarossa Alternator Belt Broke and Took Out Part of the Wiring Harness | FerrariChat
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1991 Testarossa Alternator Belt Broke and Took Out Part of the Wiring Harness

Discussion in 'Technical Q&A' started by dmoodyii, Sep 26, 2025 at 4:07 PM.

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  1. dmoodyii

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    #1 dmoodyii, Sep 26, 2025 at 4:07 PM
    1991 Testarossa Alternator Belt Broke and Took Out Part of the Wiring Harness…

    Can anyone help identify where these four wires go? The harness is a 1/4”” corrugated loom with the four wires inside, the loom ran done the passenger side front engine bank next to the crank pulley. The yellow/ red and the yellow/ black were grouped together the purple/ black dots and had the remnants of the blade connector you see in one of the photos. I think the purple / black dots and the red/ black trace went to the air pump clutch. There are two sensors on top of the oil filter housing one with a single blade the other with two. Based on the proximity I think the yellow wires go to the sensor with two. Anyone have a wiring diagram or know off hand what these four wires go to? I fixed the belt but know the car only idles it will not respond to throttle inputs…

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  2. Qavion

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    #2 Qavion, Sep 26, 2025 at 5:26 PM
    Looking at the wiring diagrams, this seems to be the case:

    https://www.dropbox.com/t/7WoJzeLhBw2PRaKX

    See (140) in the diagram.

    I'm just having trouble tracing down the black/orange (?) and the red/yellow (?). Can you confirm the colours?

    There is an orange/black (reversed colours to black/orange) power wire going to both the Water Thermoswitch (146) and the Water Temperature Sensor (145) from relay D in the engine compartment via a splice.
    I can't find a red/yellow wire other than one going to the ignition coil/power module. I don't know if that's anywhere near that harness... I'm not familiar with the TR

    https://www.dropbox.com/t/KbASZxZXC87H4xK6


    Calling @Steve Magnusson
     
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  3. dmoodyii

    dmoodyii Rookie

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    #3 dmoodyii, Sep 26, 2025 at 6:06 PM
    The colors might be orange/red and orange/ black… The two sensors on top of the oil filter housing had both connectors knocked off. The single connector sensor was easily as the plug was still intact, it come off the same harness as the Speedo pickup sensor. The two blade connector sensors plug was completely gone and I assume it’s two connectors are two of the four. Here is a shoot of the two sensors and maybe a more color accurate photo of the wires. Thanks for your help!!!

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  4. Qavion

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    #4 Qavion, Sep 26, 2025 at 8:00 PM
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    "69" in the parts manual is described as a "bimetallic thermoswitch" and 59 is described as a "switch for oil pressure LED".

    It looks like 69 controls relay "A" via an orange/red wire. Power is suppled to the bimetallic thermoswitch via the orange/black wire.

    I guess you want to know which wire goes to which pin on the thermoswitch plug, but it doesn't really matter. It's just a switch. Item 114 in the wiring diagrams.

    Problem solved? (apart from locating a new plug for the thermoswitch and a lot of splicing work)
     
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  5. dmoodyii

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    #5 dmoodyii, Sep 26, 2025 at 8:07 PM
    Thank you!!! I believe I have the wire situation sorted!
     
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  6. Qavion

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    #6 Qavion, Sep 26, 2025 at 8:09 PM
    It's this part I don't understand. I wonder what relay A does, other than controlling an air pump.

    I see it controls Relay B (Air Pump Tachometric Relay), sends an input to both engine ECUs, controls an "electrovalve" (150) and the air pump.
     

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