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Tricked by Glow when Blow-Headlight wiring upgrade?

Discussion in 'XJ Technical Chat' started by ManBot13, Feb 20, 2011.

  1. ManBot13

    ManBot13 Well-Known Member

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    So I've been having a bit of a headlight problem on my '82 XJ 750 Seca, and was probably blaming it on the wrong things.

    At first, I thought it was the head relay, because when I tested it (ignition on, but with the engine off, jumping the power and relay wires), it would click but not light the head light, and it would unclick when the jump was removed. I actually tested it RECENTLY, applying 12.5 V directly to the power side of the relay, and using an LED test light as a load, jumped the switch lead and it worked perfectly, it even stayed on.

    So with the relay removed, I jumped the power that flowed through the relay and drove around like that for a while. Sometimes, if the battery didn't have enough charge to power the headlight AND turn the starter, I could unplug the jumper wire, and start no problem. Plug the jump back in, no big deal. Until I recently found that when a turned on the ignition, the headlight wouldn't come on (with the jumper) but as soon as the engine started, the headlight would come on (my charging system output is good). I basically had the relay effect, without a relay. Neat, but this let me know that I really needed to look into the problem.

    So took my wife on a ride yesterday, and it was getting dark by the time we got back. I noticed that while my headlight was ON, it was so dim that I DESPERATELY needed to have a cager behind me just to light up the roadway.

    Turns out, I had a glow when blow fuse, that actually passed enough current to light the filament WHEN THE ENGINE WAS RUNNING (i.e 14.8 V). Since most of my riding is daylight, or well lit by street lights, I figured ON was ON.

    So that's the glow when blow. I found that the headlight relay still doesn't work when installed, but will test ok, but the headlight works when jumped. The voltage across the headlight connector leads is around 8.5 V, when the battery voltage is about 12. I lose about:
    1 V from the main fuse to the headlight fuse (across the ignition)
    0.3 V from the relay connector to the left handlebar switch connector
    0.5 V from that connector to the connector that feeds into the atari
    0.25 V through the Atari
    0.5 V to the ground.

    I know I'm missing another volt somewhere in there, but is this unusual? The headlight isn't original, but I'm thinking of upgrading the horn and was wondering if I should just install a relay block, using the current wiring to operate the relays, and run power directly from the battery, through a fuse, and to the headlight. Any advice? Should I run the actual power through the 10A headlight fuse, and just jump the current headlight fuse, since it won't actually carry the current to the headlight?
     
  2. ManBot13

    ManBot13 Well-Known Member

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    Re: Tricked by Glow when Blow, Headlight voltage drop

    So want to upgrade the electrical on my '82 750 Seca. There's just too much wire and too many switches between my battery and the headlight filament. I'd like to run power directly from the battery to the headlight using thicker wires (14 gauge?) and relays to power a distribution block from the Diode Block Signal (i.e. only powered on while running, no diode "latch"). I was also thinking of using this distribution block to power a larger horn and perhaps a cigarette lighter mount. Maybe even include a bypass switch that jumps the Diode Block signal with power from the ignition switch, in case you really need to honk at someone with the engine off, or test the relays without starting the bike.

    I'm not sure what to do with all the wires that currently carry power to the headlight. I'd need a signal from the hi beam switch to flip a SPDT switch to power the high beam. Maybe tap the tail light circuit for that signal. I don't have an Aux light, and I guess I'm really not thinking about that one right now.

    I'm wondering if anyone else has rewired their 750 seca to give a more direct path to the headlight and any other high draw devices. Is there any way to keep all of the idiot lights on the atari, if all those circuits end up being hooked up to are relays? I saw one thread on this here, but all of the pics were lost.
     
  3. RickCoMatic

    RickCoMatic Well-Known Member

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    Re: Tricked by Glow when Blow, Headlight voltage drop

    If you havent, ... Upgrade the Fuse Box.

    Run a different Head-Light BULB.

    Try the Sylvania SilverStar MC Bulb of the GE equivalent.
     
  4. ManBot13

    ManBot13 Well-Known Member

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    Re: Tricked by Glow when Blow, Headlight voltage drop

    Fuse Box is upgraded (that's why I was tricked by Glow when Blow). It's got 6 slots, 2 unused.

    The current headlight isn't stock, it's a round, suzuki headlight. I probably should get more info on that, but I'm thinking the 8.5 V that I measured across the headlight (headlight relay is jumped, running off of battery power only) isn't going to help anything. And since I was seeing losses all along the line, there isn't one short or high resistance point that I can easily fix...it's the wiring, connectors, switches, etc. that's the problem, so I want to upgrade. After upgrading the wiring, I want to consider headlights, LEDs, and other mods.

    Also, I've already pulled the whole loom, cleaned and greased all the contacts, so I'm not sure how much more I can do. Is the 1 V drop across the ignition switch (between main and headlight fuse) is a little concerning?
     
  5. ManBot13

    ManBot13 Well-Known Member

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    Re: Tricked by Glow when Blow, Headlight voltage drop

    Ok, so I've done some more voltage drop testing. Granted, I didn't do this with the bike running (off of regulated alternator power), but off of switched power, with the headlight relay jumped. I suspected a voltage drop across the ignition switch, but found that it was only 0.3V, when the voltage drop from the main to the headlight fuse is about 0.8V. So given that the harness is robbing voltage everywhere it can (and I've removed the loom, cleaned the contacts, and greased them all), I figured an upgrade in wiring is in order.

    Rather that try to rewire the WHOLE bike (and there's alot to rewire on a 750 seca), I want to wire in a distribution block that will be power switched from the Diode output. I also threw in a switch to jump the diode input with ignition power. From that distribution block, I plan to power the headlight, new horn, and perhaps a 12V socket for a GPS.

    My only question is how to save the idiot indicators on the Atari for the headlight, and if the high and low beam wires go in could be wired together on the ground side of the headlight, or if they should be wired into the hi and low side of the headlight. I don't want to fry the computer. So what do you guys think?
     

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