rossman Posted October 19, 2014 Share Posted October 19, 2014 (edited) Short version: I'm trying to get the Speedhut GPS speedo highbeam LED to function properly in my 11/72 240z. The problem is that the highbeam LED is illuminated when the headlight switch is set to parking/running (position 1) but works as expected when the headlights are illuminated (headlight switch set to position 2, high/low switch). Thru a bit of testing with the DMM I determined that the switched highbeam ground wire is grounded when it isn't supposed to be (headlights off and headlights in position 1). This is causing the relay that I installed (per KTM's thread, post #18) to activate (close) and illuminate the highbeam LED when it isn’t supposed to. Also, for the record, the stock highbeam indicator was NOT functioning prior to this gauge install. Any ideas? Details below... Extended version: The stock highbeam indicator wiring uses un-switched power from the fuse box (red wire) to the lamp and ground to the same switched ground wire it uses to ground the highbeams and thus power the highbeam lights via the hi/lo beam switch. The problem is that the Speedhut speedo expects +12v and uses its own ground to complete the highbeam LED circuit. So, I wired in a relay (per KTM's post #18) that receives power to its solenoid from the parking/running light switch (grn/wht wire) and is grounded to the same wire (red/wht) that is only grounded when the headlight hi/lo switch is switched to hi, per the FSM wiring diagram. The same parking/running light power wire (grn/wht) is also used to power the Speedhut LED via the relay NO switch (87). In this configuration, when the headlight switch is off, the hi beam LED should be off – no power and no ground to the relay control solenoid. When the headlight switch is set to position 1 (parking/running) the LED should be off – no ground for the relay solenoid. And, when the headlight switch is set to position 2 the LED should be off when the hi/lo beam is set to lo (no ground) and illuminated when its set to hi (grounded). Make sense? That's the way its supposed to work. But I'm getting ground to the solenoid when the headlight switch is off and set to position 2. So, the LED is illuminating when the when headlight switch is set to position 2. I checked continuity from the red/wht wire to chassis ground with a DMM and get the following results: [HL SW, HI/LO SW, reading] off, HI, 0 ohms (grounded) off, LO, 0 ohms (grounded) position 1, HI, 0 ohms (grounded) position 1, LO, 0 ohms (grounded) position 2, HI, 0 ohms (grounded) position 2, LO, OL What confuses the crap out of me is that the high beams function normally, meaning they are ONLY illuminated when the headlight switch is set to position 2 and hi/lo beam switch is set to hi. So why the heck am I getting continuity (ground) on the highbeam grn/wht wire in any other setting other than headlight position 2 and hi/lo switch on hi? Edited October 19, 2014 by rossman Quote Link to comment Share on other sites More sharing options...
socorob Posted October 19, 2014 Share Posted October 19, 2014 I used a relay in mine powered by the red/blue and red wire( if I remember correctly). This is a 280z. I then used a diagram from classiczcars to put in relays for the headlights. That diagram reversed the low and high beam wires so wire length would work out better. now that I have done that, my speedhut high beam indicator comes on when I put lowbeams on and goes off when I put highbeams on(reversed). When my headlights are on and key is off, the indicator doesn't light up, so the wiring is keyed on power. i don't know if whats powering the coil(the reds) or what I picked up to power the light is keyed power. If its keyed power powering the relay and light, you may be able to use a 5 position relay to make it work. Quote Link to comment Share on other sites More sharing options...
rossman Posted October 20, 2014 Author Share Posted October 20, 2014 Problem solved! I remembered today that I had forgotten to connect the Headlight Upgrade Harness that I purchased a while back. I had connected the power but never connected all of the connectors at the headlights. I thought that maybe I could figure out a way to use that harness to feed power to the highbeam light...so I went ahead and installed it. I also modified the grounds and spiced in wire to carry the ground wires all the way back to the battery. Chassis grounds suck on this old of a car. Anyway, I got it all hooked up and tested it. To my amazement, the highbeam light functions properly now! Go figure. If any electrical wizards can shed some light on this, I'm all ears! Quote Link to comment Share on other sites More sharing options...
ktm Posted October 20, 2014 Share Posted October 20, 2014 Glad you finally got it working. Sometimes lucky will suffice. I am wondering (not really thinking hard about it), if you had a floating ground issue that may have caused the problem. Quote Link to comment Share on other sites More sharing options...
rossman Posted October 21, 2014 Author Share Posted October 21, 2014 Thanks! I have no idea what was going on. It's working now so I'm not going to mess with it. Quote Link to comment Share on other sites More sharing options...
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