Testing a flasher relay

Discussion in 'CT90, CT110, ST70, ST90 Discussion' started by slickmick, Oct 6, 2019.

  1. slickmick

    slickmick New Member

    Joined:
    Sep 16, 2019
    Messages:
    3
    Likes Received:
    0
    Hi everyone! I'm in the later stages of rebuilding /restoring a 1973 Honda st90 and my blinkers are not blinking. The light just burns solid when I turn them on. Thinking it may be the flasher relay. I have a spare but it's as old as the other, so I am not sure about either's functionality. How do I test them, I hate to order unnecessary parts.
    Thanks!
     
  2.  
  3. allenp42

    allenp42 Well-Known Member

    Joined:
    Apr 1, 2014
    Messages:
    912
    Likes Received:
    250
    Flashers can be a pain and are finicky. First of all, swap the 2 leads on the flasher and see if it works. I found out the hard way that the flasher does not work when the leads are reversed.

    If that does not help or gives you the same results, I would make sure that you're using the correct wattage lamps (17w bulbs). If you have the correct wattage bulbs -and- the battery is fully charged - and- all connections are good - and- the turn signal switch does not have high resistance, then you may have a bad flasher. I think you get the point. Current flow through the flasher is what makes it blink. Anything that adds resistance to the circuit will cause the lamps to come on solid.

    Just to see if your flasher is good, try using some jumpers and with 2 bulbs connected directly to the flasher.
     
    racerx likes this.
  4. racerx

    racerx Administrator
    Staff Member Administrator

    Joined:
    Jul 10, 2005
    Messages:
    14,084
    Likes Received:
    1,459
    Anything that affects the temperature of the bimetal strip inside the unit will affect flash rate. Too much current, as you'd get with bulbs that draw more power than stock, higher-than-spec voltage, or both will result in rapid flash rate. Too little current draw, low voltage...or/and low ambient air temp...will slow flash rate, of stop it altogether.

    That finickiness allenp mentioned, is worse even than it sounds. Everything in the system: switch contacts, voltage, current draw, battery condition, ambient air temp has to be within spec,as it was when everything was minty-new, or you can have problems. Even when new, these relays left a lot to be desired on these bikes. Now, four decades later, there's a good chance of something being oxidized and that could be anything from a ground, to the switch assembly, a bulb socket contact...even the contact points inside the flasher relay. The bimetal strip can be affected by oxidation, too. IMO, the foolproof testing method is beyond the reach of virtually everyone; that would be a dedicated tester with precisely the right voltage & current draw. Thus, the best anyone can do is make sure that all of the contacts, throughout the system are clean, the DC power source can deliver 5a and 6-7v and the bulbs are of the specified wattages. Bulbs are another variable, as the nominal wattage can and will be different than the actual wattage. Unfortunately, bulbs are a dying technology, especially 6v flavor, which has 3-decade headstart toward obsolescence. Just to be clear, I'm not saying that 6v bulbs are going to disappear; but, the number of choices and quality are both in decline. It only takes a slight variation in bulb draw to affect these mechanical relays.

    FYI, oftentimes the turn signals will begin working better...if not normally...after the bike has been running for some time. I'm talking about 30-60 minutes, or more. The combination of charging the battery, engine heat and vibration seem to have a positive impact. It's just a damned slow test method.

    If you can source an electronic relay, that's the best solution. For those running 12v electrical systems, it's easy; solid state relays can be had for less than $30 and they work the same regardless of current draw. Those running 6v electrical systems have very few choices and the few that I've seen, so far, tend to be unavailable much of the time...that will likely change for the better.
     
  5. allenp42

    allenp42 Well-Known Member

    Joined:
    Apr 1, 2014
    Messages:
    912
    Likes Received:
    250

Share This Page