BSA Owners' Club Forum

The BSA Workshop => Singles => Topic started by: Phil C on 21 April, 2021, 17:20:42

Title: Stop light not working
Post by: Phil C on 21 April, 2021, 17:20:42
I recently had the brake rod off my B40 to straighten it and replace the spring on the switch, etc.. Having put it back together I see the stop light isn't working. Checking with a multimeter, there are about 5.9v across the battery. Similar at the switch, and at the switch exit. Similar at one of the two lead contacts at the light fitting. Checking the bulb, I get a low ohms reading at both contacts, not the other. The other lights all work. What's wrong?   Phil
Title: Re: Stop light not working
Post by: Rog1 on 21 April, 2021, 17:31:42
Checking the bulb, I get a low ohms reading at both contacts, not the other.

I'm not sure what you mean here. Is it a tail and brake lamp, with 5 and 21 watt (or similar) filaments? If so, you should get a low Ohms reading between both base contacts, and different low Ohms readings between each base contact and the metal body of the bulb.

Was the stop light working before you took the rod off? Check the switch operation by putting the meter probes across it so that you get your 5.9 volts, then operate the brake lever. The voltage should fall to zero. If it doesn't, give the spring a tug and see if that does it.
Title: Re: Stop light not working
Post by: Phil C on 21 April, 2021, 17:59:54
Sorry, should have explained more clearly. It's a two-filament (21/5w) bulb (tail light and stop light.) Using the multimeter, across the battery terminals I get about 5.9volts. Then keeping one meter lead on the battery earth, I check for readings along the circuit by putting the other lead at various points: at the switch (near the brake pedal) I get a similar reading (about 5.8-5.9.) At the other contact of the switch (only if operating the brake pedal) I get roughly the same. At the light fitting, having removed the bulb, I see two contact points. One reads 0, the other about 5.8-5.9v ( again, operating the pedal.)Is that what I should get?
Regarding the bulb, visually it looks okay. I get a low ohms reading across its two contacts, and when I connect each contact with the metal wall. 

The other lights all work, it's just the brake light that's not working.  Could anyone tell me where the problem is please?

Phil
Title: Re: Stop light not working
Post by: Phil C on 21 April, 2021, 18:07:27
A bit more info: re the contact in the light fitting where I got a zero volt reading - if I turn on the tail light switch (!) I get a reading of about 5 point something volts. Phil
Title: Re: Stop light not working
Post by: Pete A10 on 21 April, 2021, 18:45:13
Couple of things to check - is one filament of the bulb blown? Also check that the switch (by the brake pedal) is pulling on completely - try operating it by hand. If you have got power everywhere then it must be a failure of one of the components.
Title: Re: Stop light not working
Post by: Phil C on 21 April, 2021, 19:00:49
Filaments look good visually. Low ohms readings on the bulb. When I operate the pedal there are volts at the light fitting contact point. I don't get it. Maybe something very obvious I'm missing? Probably something to do with me having the rod and switch off I guess, but what?  Phil
Title: Re: Stop light not working
Post by: Calum on 21 April, 2021, 19:39:39
If you're getting 6v at the terminal in the bulb holder with the switch pulled then the wiring up to there should check out... SHOULD.
Multimeters will show a voltage reading when the current is so so very low, so sometimes a dry/broken joint might still show as transmitting power but as soon as you actually load the circuit up (with a bulb or whatever) then sometimes the joint then 'fails' and there's 0v. In many cases a test light is mich better for fault finding (easily made with a bulb holder, some wire and a pair of crocodile clips or similar)

On the other hand I think your issue is probably an earth issue, or the bulb. You said the multimeter was connected to the battery earth. Try the meter across the bulb contact and the base of the lamp unit, or check for continuity between lamp base and battery earth.
Title: Re: Stop light not working
Post by: idie on 21 April, 2021, 20:00:28
Remove both wires from the switch and touch them together. Does the light come on, which it should do. If the bulb lights then the fault is with the switch not carrying any amps. If the light does not come on then the fault is with either the bulb holder or the bulb.
Title: Re: Stop light not working
Post by: Blackthou on 21 April, 2021, 22:06:52
This is quite a common occurence when moving the brake rod / switch. Try as Rog1 suggested, give the spring a tug and it will probably come on. It's then a question of sliding the switch anchor along the rod until the light comes on then back it off a bit.

Good luck
Title: Re: Stop light not working
Post by: ducati2242 on 21 April, 2021, 22:07:02
You say you are keeping multimeter on the earth on the battery . Are you sure the earth on the tail light is actually working you should be able to read 5.9 volts at the bulb holder earth being the bulb holder and live at the correct terminal from the brake light switch .
Title: Re: Stop light not working
Post by: Phil C on 21 April, 2021, 22:22:53
Thanks everyone so far. Just been out in the garage. Continuity between the lamp housing and the battery earth terminal seems okay (beep on meter) but between the light unit bulb contact and the battery terminal there doesn't seem to be continuity. So it seems the problem is the connection between the light unit bulb contact and the lamp housing. Is that right? Not sure how to sort it yet - all advice much appreciated. I think (see photos) it's a non- standard fitting, maybe off a Honda?   Phil
Title: Re: Stop light not working
Post by: Phil C on 21 April, 2021, 23:00:47
But it stilll seems a bit too much of a coincidence that I've noticed the brake light not working straight after I've had the brake rod off. Tomorrow I'll try as Blackthou suggests and if that doesn't work then look into that earth connection.   Phil.
Title: Re: Stop light not working
Post by: Phil C on 22 April, 2021, 08:05:58
Stupid of me - of course the bulb is the link between the bulb connector contact and the light unit. So it's still s mystery. I'll check everything again.  Phil
Title: Re: Stop light not working
Post by: Phil C on 22 April, 2021, 11:49:04
There will if course be a logical answer, but it's escaping me at present. The key factors I'm seeing are:
1. The bulb is good (tested with meter and made  both filaments light using spare wires on the battery.)
2. I have 5.8 volts at the bulb holder contact point (measured by multimeter with one wire on the contact point and the other on the battery earth terminal.)
3. There is continuity between the lamp unit and the battery earth terminal (beep on multimeter.)
The only remaining place where there could be a break in the circuit I think is where the bulb connects to earth, but the tail light works so that would seem unlikely.
What am I missing here? Something really obvious maybe?
Phil
Title: Re: Stop light not working
Post by: Phil C on 22 April, 2021, 12:03:23
Further to my post just now, I guess there are actually two possible places where there could in theory be a break: both the bulb contacts. But as the tail light works that would seem unlikely. What am I missing here?  Phil
Title: Re: Stop light not working
Post by: DAVE BRADY on 22 April, 2021, 12:12:58
Hi Phil,

The tail light filament can work even if the stop filament is blown. If it is not obvious try another bulb.  I think you have established that there is power to the switch so as has been said disconnect the two wires from the switch and touch them together.  The stop filament should light.  If it does then the problem is in the switch.  Give the switch a bit of a work out by repeatedly operating it over its full movement to re-establish the internal contact and perhaps a bit of contact cleaner. 
A bit of a simple one but is the movement of the brake rod actually operating the switch?

Dave.   
Title: Re: Stop light not working
Post by: Phil C on 22 April, 2021, 12:23:38
Hi Dave, I've tried touching the two switch wires together: the bulb didn't light. I've tried moving the switch on and off but that made no difference. With the brake pedal depressed I have volts at the bulb holder contact, so it seems to me the switch is okay. I can't think of anything other than the connection between the stop light filament and the lamp body. I guess I could try another bulb, but I'm a bit loath to as I know both filaments work.  Any other ideas anyone please?  Phil
Title: Re: Stop light not working
Post by: DAVE BRADY on 22 April, 2021, 12:29:54
Hi,

If you have a spare bulb you have nothing to lose giving it try as a process of elimination.

Dave.
Title: Re: Stop light not working
Post by: Phil C on 22 April, 2021, 12:40:45
True. I'll buy one this afternoon. Fingers crossed.  Phil
Title: Re: Stop light not working
Post by: Rog1 on 22 April, 2021, 13:28:59
If no joy with a new bulb, use a test light (as Calum suggested).

First connect the test light between the battery side of the switch and earth. If it doesn't light, the problem's in the wiring to the switch.

If it lights, connect it between the brake light side of the switch and earth, and operate the switch. If it doesn't light, it's the switch.

If it lights, connect it between the brake light side of the switch and the earthed part of the tail/brake light bulb holder. Operate the switch. If it doesn't light, it's the earth.

If it does light, the problem is between the switch and the brake light. Then, you might have a broken wire that was undetected until it was disturbed.
Title: Re: Stop light not working
Post by: Phil C on 22 April, 2021, 14:08:10
Thanks Rog1. I haven't yet got a new bulb (going to get one later today), but have just tried what you advise. The test light comes on each time, so if the new bulb doesn't work then I need to look at the wire between the switch and the light unit. Thanks again. Ph
Title: Re: Stop light not working
Post by: MGI on 22 April, 2021, 16:27:26
Have you checked the actual spring unit is making contact?
Title: Re: Stop light not working
Post by: Phil C on 22 April, 2021, 17:28:10
Er...how do I do that? I'm suspecting the problem is within the light unit.
Title: Re: Stop light not working
Post by: DAVE BRADY on 22 April, 2021, 17:35:40
Hi,

I think MGI means the spring loaded part that has the contacts on.  If you get your little finger and push the contacts in where the bulb goes it should move quite easily and spring back up.  Also, some times if there has been a poor connection a bit of corrosion can occur on the contacts so make sure they are clean. A bit of a scape with a small blade will do it but switch off the power or you may blow the fuse. 

Dave.
Title: Re: Stop light not working
Post by: Phil C on 22 April, 2021, 17:47:27
Oh yes, the spring operation seems fine.
Title: Re: Stop light not working
Post by: Phil C on 22 April, 2021, 18:51:37
Amazing. It was the bulb. I checked the duff one three ways: visually, with a multimeter for continuity( gave a healthy beep), and with the battery on the bench and a couple of bits of old wire( both filaments lit up.) The two contacts on the bottom of it look fine. I assume the earth connection on the bulb is the metal housing which fits into the female bayonet fitting, in which case it too looks fine. I wonder what's wrong with it. But anyway, I put in a new bulb and it worked.  Thanks again everyone. Good practice for me!  Phil
Title: Re: Stop light not working
Post by: Rog1 on 22 April, 2021, 20:22:05
Good news! One take away from this is before taking something apart, check if it's working first; I've been caught out like this in the past.
Title: Re: Stop light not working
Post by: Phil C on 22 April, 2021, 21:26:47
I wonder what was wrong with the old bulb.
Title: Re: Stop light not working
Post by: Stubaker58 on 22 April, 2021, 21:43:40
Could it be that the contact on the base of the bulb is not actually touching the bulb holder contact when the bulb is inserted?
Title: Re: Stop light not working
Post by: courtney on 23 April, 2021, 16:48:51
What an illuminating topic.