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Highbeam Solenoid Only Has 4.5v??

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  • Highbeam Solenoid Only Has 4.5v??

    I was doing my retro over the weekend and noticed the highbeam solenoid was not triggering (using RX350 projectors.) I ended up breaking a projector so I reverted back to stock, but didn't plug in the highbeam wire on either light since I had already changed the connector. The stock lights are halogen projectors with a highbeam solenoid. I wanted to test the wires last night to see if I could figure out why it wasn't triggering and what I found has me stumped.

    With the projector (stock) not plugged in I get a nice strong 11.5v signal on the high beam signal wires. If I plug in the stock projector and probe the wires then I only get 4.5v when I hit the high beam switch. I tried all sort of variations: car off-manual lights on, car on manual lights on, car off auto lights, car on auto lights, halogen bulb plugged in and also unplugged but no matter what I tried I always would only get 4.5v when I plugged in the stock projector. I only had the driver side plugged in while testing with the stock setup last night. Over the weekend I had both RX350s plugged in when it also didn't work, so I suspect I was only getting 4.5v then too. The only thing left really to try is unplugging everything on the passenger side to isolate the driver's side for testing. Does anyone have any idea why the volts drop to 4.5v simply by plugging in the stock projector solenoid? I was not using the wiring HID wiring harness I made while testing last night, everything was in a stock format minus the passenger side solenoid being plugged in.

    I found this from googling. Unplugging the passenger side and driver's side bulb should help me know if things are crossed. I really don't think they are though because I made to sure to check how the wires were placed in the stock connectors and marked which lead was (+) on the connector before I disassembled them. Everything worked fine with the HIDs low beam, and also with the stock's just that the high beam solenoid does not trigger. :/
    The blown fuse was part of the scenario I was thinking of.

    If you look at the diagram: The RH hi-beam has 12V on it all the time but it only operates, like the LH hi-beam, when the ground side is connected to the dimmer relay contact as shown. Normally, as soon as you turn the lights on, the dimmer relay switches to ground the low-beams (unless, of course, you have left the hi-beam steering wheel switched to HI).

    In your case, with the blown LH lamp fuse (or it could have been a bad LH relay also), there is no 12V potential to drive current through the LH bulbs to ground normally (in either hi or low position).

    BUT, as the hi-beam bulb grounds are connected where their grounds, as shown, join at the wire crossing (joining) next to the jumpover for the RH low beam ground, the 12V after passing thru the RH high beam is finding its way back thru the ground wire to the LH hi-beam and also thru the LH low-beam (the 12V, except for the fuse being blown, normally feeds both bulbs at once, so their inputs are tied together), and then to the low beam ground on the dimmer relay.

    The 12V at the RH hi-beam is reduced thru 3 bulbs on its way to ground, so all three glow at ~1/3 brightness.

    The RH low-beam acts normally because its circuit is direct to ground.

    If the fuse was not blown, you would have 12V at all the bulbs and the current would be forced to flow the normal way thru the bulbs to ground, depending on which way the dimmer was "set".

    The hi-beam dash indicator after the voltage drop thru the two high-beam bulbs is not getting enough voltage to fire it to ground.

    You would see 12V on the multimeter as you said because with the plug disconnected no current is flowing so you don't see a voltage drop thru any of the bulbs until you plug it back in.

    When, in hi-beam mode, you disconnected the LH low-beam you broke the circuit to ground, so the LH hi-beam went out, too. And the RH side hi-beam worked because it was going directly to ground as it should in the Hi-beam mode.

    I think that's all there is.

    More: Crossed grounds would do the same thing, but only if the fuse or relay were bad.

  • #2
    I just got my retrofit from plugged up today. Decided to function check them before bolting everything up. Also RX350s. I'm having a similar issue. No idea about voltage. I need a multimeter. My solenoids won't go to high beam. Also, my dash High beam indicator is constantly staying on, but dim when the low beams are on.

    My "off with high beam" fogs turn on initially, but after attempting the high beam, they won't turn back on with low beam unless I turn the headlights off and back on entirely


    • #3
      Do you have a copy of the wiring diagram for your factory lights?


      • #4
        To update this:
        I finished the retrofit this weekend finally. I tested the RX350s by touching the solenoid wires directly to the battery and it worked. I then did the same with the stock projector and figured out which lead was (+). After doing so I realized that the RX350 solenoid plug I already wired in had the wires backward. I felt pretty stupid lol. I flipped them around and then went back outside to test. Everything functioned normally. I didn't retest the stock projector since I had issues with that originally....but I suspect that when I plugged in the wires directly to the projector that they were backward as well.