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aldabra82

Override the stop light sensor for LED bulbs

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I put some new BRIGHT Stop/Tail light LEDS in my 82ZX, and a new flasher that works with LEDS but still need to override the sensor that controls the little display on the dashboard, that says the bulb is burnt out. I see in the FSM (pg EL-73 ) the RL and RG wires to the box under the passenger seat. Taking it apart, there are two coils with reed switches inside of them.
StopLightSensorGuts.jpg.f91689ad8f5ebd068e29bfd9eef90aac.jpg
Measuring from RG to ground I see 2.7 Ohms with all the incandescent bulbs in.
image.png.ecafe38bcca3d0dd47c4b7496daa6ed0.png

This says to me that I need to draw 12v/2.7ohm = 4.4 amps or 4.4A * 12V = 52 Watts!!! That seems reasonable to me given that there were 8 incandescent bulbs on that circuit originally.

 

BUT I don't want to put a huge HONKING resister to fake out the the display, has anyone come up with a better idea? Anyone manage to outsmart the sensor?  

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So I assume the reed switches are supposed to change state when enough current is being drawn through the coil, and that lack of state change is what triggers the dash light.

 

If the reed switch is normally closed, you need to desolder one leg to leave it always open. If it's normally open, you need to jumper across the reed switch to make it always closed.

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The reed switch is normally open, according to my Ohm meter.  If I put a magnet on the reed switch,  I can force it to a closed position. In that closed position the display shows that there is a fault. That does not make sense. The switch is normally open but when a current runs thru the coil  to the tail/stop  lights the switch closes... So maybe it has to be open initially when the key is turned, and then when the brake lights are energized it the switch is closed ( or not if the bulbs are bad) and that is how the sensor works. Maybe the next step is to un-solder the reed switch and then measure when it is closed or open during the "key on" state and the and "break pedal push" state. 

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