brake light switch

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brake light switch

Postby David Richard » 22 Jul 2018, 09:27

this is not funny any more ,has any one had a problem with 750 front brake light switch I have replaced 3 genuine parts on mine in 300 miles ,I have 21 k on it I have had no other bulbs or electrical problems with the bike ,am I missing something I have taken a old one apart to have a look its only springs and metal strips and cant see anything a miss .I spoke to cradleys to ask if they have a bad batch but has anyone had a problem ,or what can I look for thanks david
David Richard
 
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Re: brake light switch

Postby Freddy » 22 Jul 2018, 11:55

David Richard wrote:this is not funny any more ,has any one had a problem with 750 front brake light switch I have replaced 3 genuine parts on mine in 300 miles ,I have 21 k on it I have had no other bulbs or electrical problems with the bike ,am I missing something I have taken a old one apart to have a look its only springs and metal strips and cant see anything a miss .I spoke to cradleys to ask if they have a bad batch but has anyone had a problem ,or what can I look for thanks david


Given mines still running the original switch after 21 years and 160,000 kilometers, I think I'd be checking the current draw through the switch to see if there is a short or something like that that is burning out the switches. I'm assuming it's an electrical rather than a mechanical failure your continuing to experience.

The genuine workshop manual is down in the garage and it is cold outside being Winter night time here (which probably equals a typical British summer day, sorry couldn't resist). I don't know if it has any electrical testing numbers but sing out if you would like me to have a look. But regardless I think if there isn't a short circuit the current draw should only be equal to that of the stop light bulb. If its labeled in watts (typically), just divide by 12 to give the expected amperage draw.
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Re: brake light switch

Postby David Richard » 22 Jul 2018, 20:28

hi thanks for the reply I will get my multi meter out tomorrow and try and see what current is there ,I don't like electrics I will post what I find but I will also have a look in my book at the wire diagram ,but thanks again I did sort o rings for the carbs as you say they are a strange size do you think that was done by mistake ,hey we are having one of the best summers over here for many years its a bit hot and nearly a drought but I go out very early if only it would last longer ,david
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Re: brake light switch

Postby Freddy » 23 Jul 2018, 03:51

David Richard wrote:hi thanks for the reply I will get my multi meter out tomorrow and try and see what current is there ,I don't like electrics I will post what I find but I will also have a look in my book at the wire diagram ,but thanks again I did sort o rings for the carbs as you say they are a strange size do you think that was done by mistake ,hey we are having one of the best summers over here for many years its a bit hot and nearly a drought but I go out very early if only it would last longer ,david


A typical 12 volt stop/tail bulb is 21/5W. So that means the stop light should draw 1.75 amps. That's more amperage than the 'regular' connection on a basic multi-meter, so if you have that type be sure to move the positive lead to the typically 10 amp max connection.

good to see you got the o-rings sorted. You'd have to assume what was in there were the originals, and why the carby manufacturer decides on that size, who knows.

Hot and drought, your talking to an Australian, that's just everyday of the year weather here. Don't know why you crew are so slow to figure something out. My Great-grand parents figured it out about 150 years ago. :D
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Re: brake light switch

Postby David Richard » 23 Jul 2018, 05:53

hi thanks for the info about amps ,im off to work shortly but will have a look tonight,we moan when its rubbish weather and look forward to this but its just to much thanks david
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Re: brake light switch

Postby David Richard » 23 Jul 2018, 20:16

hi ok I have had a look I have the correct bulbs in ,and I swapped the red lead into the 10 amp max set the dial to 10 and connected to the wires ,it read 3 .25 with the engine off ,I then pushed the leads back on and it read the same ,I have a spare right side switch gear with low use on it ,I connected that to the loom plugs and that read 3 .16 so not a lot of difference there .the old switch I changed yesterday I did a continuity test and that is still working intermittently ,so something is amiss am I wright in thinking dirty connections may course this ,if I hold the old switch and I it does get warm to the touch what do you think ,david
David Richard
 
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Re: brake light switch

Postby Freddy » 24 Jul 2018, 03:26

David Richard wrote:hi ok I have had a look I have the correct bulbs in ,and I swapped the red lead into the 10 amp max set the dial to 10 and connected to the wires ,it read 3 .25 with the engine off ,I then pushed the leads back on and it read the same ,I have a spare right side switch gear with low use on it ,I connected that to the loom plugs and that read 3 .16 so not a lot of difference there .the old switch I changed yesterday I did a continuity test and that is still working intermittently ,so something is amiss am I wright in thinking dirty connections may course this ,if I hold the old switch and I it does get warm to the touch what do you think ,david



Get a new stop/tail light bulb. Connect it straight to the battery (any charged 12v battery for that matter, you car battery may be more accessible) in series with your multimeter. See what amperage the bulb draws.

The switch is getting warm indicates its carrying excessive current. My calculation of the expected current (1.75 amps) of the bulb says too much current. Watts = amps * voltage. Move them around and Amps = watts/voltage. 12 volts, 21 watt, 1.75 amp expected current draw.

But testing it directly at the bulk will tell you exactly what a new bulb draws. I can't think of anywhere else in a brake light circuit that would draw addition current to that of the bulb. If anything I'd expect the draw to be less than theoretical due to small voltage drops along the circuit.
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Re: brake light switch

Postby Freddy » 24 Jul 2018, 03:40

As it just so happen, I had a 21/5W stop/tail light bulb down in the garage with a couple of leads soldered to the connection from when I was wiring up my caravan electric brakes.

Went and tested the current draw, close enough to theoretical at 1.8 amps. Like any problem solving with mechanics, start with the simplest and cheapest possibility, fit a new 5/21w stop/tail light bulb.

Then if the current draw through the switch remains at 3.25 amps start hunting down where the extra current is going.
Last edited by Freddy on 24 Jul 2018, 12:57, edited 1 time in total.
Freddy
 
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Re: brake light switch

Postby David Richard » 24 Jul 2018, 05:21

hi freddy yes tanks for the time you spent in the garage ,yes I will start at the bulbs and see what happens ,david
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Re: brake light switch

Postby Freddy » 24 Jul 2018, 13:07

David Richard wrote:hi freddy yes tanks for the time you spent in the garage ,yes I will start at the bulbs and see what happens ,david


And just a further thought, also test the current draw through the switch with the stop light bulb taken out. On the basis that I wouldn't expect any relays etc to down stream of the handle bar brake switch and just a simple wire from the switch back to the bulb via a few connectors, with the bulb removed I'd expect zero current draw.

If the new bulb and testing the current draw without the bulb still shows a problem, next thing I'd do is disconnect the foot brake switch. I'm pretty sure that it has a connector behind the right hand side cover. It joins into the circuit so disconnecting it eliminates it as a problem point.
Freddy
 
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