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gastephens

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  1. gastephens's post in High Beams Won't Turn Off (Sometimes) was marked as the answer   
    This is a '76 2002 with the separate fuse for low and high beams. All that verbiage and I forgot to mention that explicitly.
     
    Good news, problem solved, or at least band-aided successfully. Here's what I did.
     
    The Susquehanna relay harness plugs into one of the factory headlight connectors. The other connector is unused. When the factory dip / turn signal switch sends power to the headlight connectors they are used as the activating signal for the high-power relays in the aftermarket harness. Those relays route power directly to the headlight and prevent high current from running through the headlight switch or the dip / turn signal switch which would eventually kill them.
     
    Random Note: If you upgrade your headlights (or even if you don't), install a headlight relay. This will do 3 good things
    1. save your headlight switch from wearing out due to high current
    2. make your headlights brighter because power is going directly to them
    3. add an extra fuse for the low/high beams, especially for the early cars
     
    Ray at Susquehanna provided the clue I needed. The relays turn on when 8+ volts are applied and turn off when input voltage drops below 3 volts. I plugged a voltmeter into the unused factory headlight connector to monitor the voltage that was going to the high-beam input of the aftermarket harness. When I activate the high-beam switch the voltage goes to 11.5V which turns on the high beams. When I deactivate the switch, the voltage dropped to 2.9V, right on the edge of deactivation. When driving, the alternator raises all voltages so the "off voltage" would be above 3V and keeping the relay from turning off.
     
    Theoretically a resistor between the high beam signal and ground would pull down the voltage enough to allow the relay to work properly. I calculated a 50 ohm resistor would drop it at least .5V and draw only about an additional 0.2 amps when the high beams were on and .01 amps when the headlights were off but the ignition is on. The resistor would need to be rated for 10 watts to dissipate that current.
     
    I soldered some spade lugs on a 50 ohm 10 Watt ceramic resistor and inserted it across the unused headlight connector. Voltage when high beams were activated was not affected. Voltage dropped to around 2.3 V when the high beams were deactivated. This made the relays snap off like they are supposed to.
     
    So problem solved. This shouldn't create any additional problems but the question remains -- where does that mystery 3 volts come from when the factory high beam circuit is turned off? I unplugged the aftermarket harness and just measured the output coming from the factory high-beam relay and it was 2.9V. This is the voltage coming through the dip / turn signal switch, which must be the problem. Since new switches are going for $250 I will stick with my band-aid for a while or until I can find a good used switch.
     
    Thanks for all your help and suggestions.
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