Reversed polarity, lose all electronics when key turned

  • #1

    Reversed polarity, lose all electronics when key turned

    I reversed the polarity when installing a new battery in my Z (I know, shithead mistake but I’ve forgiven myself) When connecting it properly, I noticed to have all electronics working, including radio and fuel pump, until the moment I turn the key to crank the engine, then all power cuts out and returns a few moments later when I’m not looking. I pulled my ecu and nothing looks fried, and ran a test light on my fusible links, which all seem to be receiving power (unless it’s the grey link that’s removable, in that case I’m not sure how to test, but the diode going to it gets power)
    Could it be the grey link? Alternator diodes? Starter? ECU?
  • #2
    You might be overloading some junction somewhere that likely got smoked when the polarity was reversed.
    It generates heat from the current draw, opens the circuit then when it cools down you get powerback. At work i'd use a FLiR camera to find the hotspot.

    You might need to study the electrical diagram in the back of the FSM. But you seem like you're getting close.


    84 AE/Shiro #683/Shiro #820/84 Turbo
  • #3
    I went ahead and pulled each fusible link at a time to find that each had a working function of some kind, which tells me they’re likely ok, however at some point (I think when I pulled the green link) instead of the power cutting out, turning the key seemed to have drained the battery and voltage returns immediately when the key is in normal position. The green seems to work as I lose power window operation with it disconnected. I think this is merely a result of fiddling around, and I’ll be back at square one once I charge the battery back up.

    After extensive research however, I do believe to have found a highly likely culprit, but haven’t been able to find any information on it.

    https://imgur.com/HwWVkMH

    Original thread:
    https://z31performance.com/forum/z31…-mystery-relay

    I’m pretty sure this refers to this orange relay that I previously was not aware of:
    https://imgur.com/a/3S85TsJ

    Will I have to pull one of these from another Z? Is there more information on this orange relay?