'72 r75/5 charge light stays on when key is pulled...

Discussion in 'Airheads' started by Echolake, Apr 17, 2013.

  1. Echolake

    Echolake Echolake

    Joined:
    Oct 22, 2012
    Oddometer:
    11
    Location:
    Snohomish, WA
    Help! I was out riding today and noticed that the charge light stayed on when the key was pulled. The bike was the very difficult to start (Starter seemed to be not engaging) but finally did start and I rode off. 10 miles later a noise developed that sounded like it may be the starter running away. after a mile or so that sound went away so I rode home (another mile or so). The charging light is still on when the key is removed and when I insert the key to try to start the bike the charging light goes off but it sounds like the starter is having trouble engaging. I'm thinking it may be the starter relay but I'd like some other opinions before I spend the $125 on the part. Any ideas??
    #1
  2. kixtand

    kixtand Long timer

    Joined:
    Apr 24, 2004
    Oddometer:
    2,223
    Location:
    Lexington, KY
    First thing is to disconnect the return to the battery. Secondly, the starter relay shouldn't have anything to do with said light... let me find the wiring diagram and I'll have some more insight shortly...

    kix
    #2
  3. Bill Harris

    Bill Harris Confirmed Curmudgeon

    Joined:
    Sep 20, 2008
    Oddometer:
    9,746
    Location:
    backwoods Alabama
    On a /5 the starter relay might be involved-- remember, the relay also functions as a lockout to keep the starter from engaging when the engine is running by monitoring the charge light, so there is a wire connecting the two. And given the odd operation of the starter, who knows what all is amiss. I'd advise the OP get a schematic and start tracing wires...

    --Bill
    #3
  4. Pokie

    Pokie Just plain Pokie.

    Joined:
    Apr 4, 2013
    Oddometer:
    2,065
    Location:
    Fort Collins, CO
    Most likely is a fried diode board. When taking off the front cover of a /5, if you drag across the diode board, it will soon be history. If a diode goes (depending which one) power will run backwards through the once "one way" gate and cause the charge light to glow.
    #4
  5. Plaka

    Plaka Brevis illi vita est

    Joined:
    Jun 19, 2010
    Oddometer:
    4,625
    Starter relays don't cost $125. It's an ordinary relay and costs $6 for the nicest one at any auto parts store.

    The /5 has a starter protection relay that cuts the starter circuit when motor is running (in case your tank bag tries to push the starter button). If it dies bike won't run. Costly to replace. Easy to just throw it away and put a momentary push button in it's place. To start the bike you hold down the momentary switch and hit the starter button. So you get the protection and a bit of anti-theft as well. You gotta know about that momentary to start it with a nail.

    I was using bar end mirrors so I put the pushbutton in the hole from one of the stock mirrors on the right bar. Easy to hit both buttons with one hand, the added button didn't get hit by accident and it would take pushing both to operate the starter. This was after two of the protection relays died.

    You always disconnect the battery ground before pulling the front cover. This fixes the problem with hitting, and shorting, the diode board. If they don't overheat they last a long time. Aftermarket replacements are popular and generally superior---for less cash. But it has to match your alternator. If you are still running a 180W it's worth getting the early /6 one from a boneyard.
    #5