/5 wiring

Discussion in 'Airheads' started by oldroadie, May 1, 2013.

  1. oldroadie

    oldroadie Two wheel addict

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    Feb 28, 2010
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    783
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    My battery is not charging.

    My wiring harness has a few repairs but appears to be stock and mostly intact.

    I have the correct lamp in the instrument cluster, it goes out once the motor is turning. I have 14V DC output from the diode board, tested at the spade lug on the board (or nearly 14V as near as I can tell holding the probes ith one hand the throttle with the other.)

    That output is not making it to the battery. I suspect wiring failure. The output of the diode board is not run directly to the battery as shown in the early /5 schematic, or at least I can't find the proper junction.

    Who wants to tell me where the output of the diode board runs thru the harness without a lecture about Clymer, search engines, or general hoo ha so I don't have to pend my one day off not riding?
    #1
  2. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    On the /5's, the output of the diode board (Terminal 30, on the left side of the board, two 10mm spade connections with a heavy RED wire to one of them) has a circuitous path back to the battery. From the diode board it goes to Terminal 30 of the Starter relay (two 6mm spade terminals with heavy RED wires). From there, one wire goes to the Switch board in the headlight bucket (and to the rest of the wiring) and the other wire goes (ta da...) to the battery. That terminal at the Starter relay is the weak point-- double terminals, riveted together, after decades a poor connection can result. Or, with age and battery acid, the red wire at the battery can corrode inside the insulation sheath.

    One fix? Run an extra jumper wire (12 Ga) from that second (unused) 10mm spade terminal on the diode board output to the big terminal (8mm, so you'll need a 5/16" ring terminal) of the starter solenoid. This way the alternator output has a good connection back to the battery. This jumper wire is supplied with some aftermarket alternators and IIRC, is the the way later BMWs connect the alternator to the battery.

    Clear as mud??? :D

    --Bill
    #2
  3. oldroadie

    oldroadie Two wheel addict

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    Thanks, Bill, that's a great help. I'd though about using that open post to go back to the battery but the starter post is much closer and will be neater, too.
    #3
  4. ritetwist

    ritetwist Been here awhile

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    Good response Bill. Concise and to the point.
    That is the way to answer a question IMHO.
    Must be good, I understood it.
    Even I could do electrics explained that way.
    #4
  5. Renner

    Renner combustophile

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    I had the joy of discovering this once... looks fine till pulling back the insulation reveals a mess of corrosion :eek1

    This on the primary lead to the starter, black-sheathed in my case.
    #5
  6. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    Darn, and I dashed that off just before going out for a ride today. He did say no horsepucky.

    I've seen sneakily-bad battery cables for years. One cure is to get a new lug the right size and heaviness, cut the old off, strip the insulation back to inspect and clean the wire, solder the new lug back on and re-insulate with multi-layers of heat-shrunk tubing. I'm on my second ground cable, still on the original starter cable. It'd do Rip VanWinkle proud... :D

    --Bill
    #6
  7. bpeckm

    bpeckm Grin!

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    Amen, good response....!! Wiring is all about conductivity: good wire, good connections. You cannot go wrong by using a larger-gauge wire, or doubling up with a new one..... All those connectionsl go downhill from day one.....!!

    And DC wiring is NOT just about the + wire... the grounds are equally critical. I ground my harness every chance I can, everywhere I can... it ALL helps, and it all works together....

    :evil
    #7
  8. oldroadie

    oldroadie Two wheel addict

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    Ah, Bill...you've set me on a new path. At least your workaround confirmed that previous owners completely bodged the wiring. Looks like I'll be rewiring the charging circuit and ignition to match the schematic and trying to determine what they thought they were doing.
    #8
  9. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    Straightening out the electrics is always a righteous pastime on an old bike. A couple of years ago I went ahead and replaced my 38 year old Engine Wiring Harness and Main Wiring Harness. I'd been patching and resurrecting them for years. The prices aren't bad-- $55 and $70-- and all-new everything gives peace of mind. I'm also a packrat, and if you are on a budget with bodged wiring, I still have the old Main Harness and probably the old Engine Harness and I'll be glad to mail them to you. Or is you are attending the Huntsville Great Chicken Rally on Memorial day, I'll bring them along. PM an address if you want them snailed.

    One thing I did years ago to help working on the wiring was to make several xerox copies of the 8-1/2 x 11 workshop manual schematic and highlight in color the circuit subsystems. I had one for Ign-Start-Chg, Stop-Turn-Horn, Main Bus, and so on. Highlighted each circuit in Red-Blue-Green felt-tipped pens on the subsystem sheets. Really helps to break things down like that, and even the process of going through and highlighting the circuits familiarizes you with the circuitry.

    --Bill
    #9
  10. Beater

    Beater The Bavarian Butcher

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    Bill - Do you have a link to the new wiring harness? I was trying to search for it ... pretty sure Robert (wirewrkr) left a link somewhere, but I can't seem to locate it ... Thanks in advance ...
    #10
  11. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    #11
  12. oldroadie

    oldroadie Two wheel addict

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    Thanks for the offer, if I can't make some fair progress I'll shoot you an address. I have lights, horn turn signals brake light, ignition...I just need to straighten out the charging portion and get the wires to the proper destinations.
    #12