tail of two filaments

User avatar
reginald

tail of two filaments

Post by reginald »

Greetings all, can anyone diagnose this odd tail-light behavior for me ?

'76 GT750A, un-Butchered, just a few safety / reliability upgrades. New OEM stock harness .

I can't seem to get the rear taillight to work as both a running light AND a brake light, and Yes I do have a good dual-filament incandescent bulb in there. Testes the 3-wire connector block and it all looks intact. Each separate function can be prompted to work, but not the whole Orchestra together, as it were.

with Engine shut off / Ignition switched on, I get a nice bright running light , bright green neutral light, but practically zero additional "brake light",when using foot or hand brake lever, it's just a smidgen brighter than the running light. Wife following on her bike says it's impossible to tell the difference brake or no brake. Tested this in quite a dark evening on a country road. .

With headlight on low-beam, I get a dim running light, and again a paltry excuse for a brake light when stood on.
With turn signals on , all 4 will light up fully but not flash. OEM relay flasher is tested and OK.

With Engine running (one push on button), I get a bright running light and again a tiny hint of a brake light on either lever. Engine running and turn signals light and Flash fully.

HI-beam indicator, neutral and turn indicators all working with Engine running at idle .

Any idea why I cannot have a full-bright running light AND a brake light too ? :tw

Thanks in advance for any clues to the missing candle....

Gary M / Ontario / Canada
Attachments
EBC upgrade.jpg
User avatar
Alan H
Posts: 12104
Joined: Fri Aug 05, 2011 6:38 am
Location: Wombwell, Republic of South Yorkshire

Re: tail of two filaments

Post by Alan H »

Bad earths and dirty connections. I haven't access to wiring details while I'm on hols, but basically pull ALL joints and clean ALL connections especially main earths if you have wiring ussues. Remember these bikes are now 40+ years old.
Proof that four strokes are over complicated
User avatar
canaletto5
Posts: 5228
Joined: Tue Jul 23, 2013 8:43 pm
Location: Derbyshire

Re: tail of two filaments

Post by canaletto5 »

How old is the battery?
User avatar
reginald

Re: tail of two filaments

Post by reginald »

Thank you Gentlemen, will do a thorough exam of all connections on coming weekend. Inside Headlight bucket too of course.

here's hoping it could be something that 'basic'. One can of contact cleaner please, bartender.

Battery is , I think, on it's 3rd year now, hasn't been an issue. I'll Tender-charge it again anyway just to know.

Cheers,
Reginald
User avatar
BATTS
Posts: 441
Joined: Sun Jul 15, 2012 6:47 pm
Location: Lancashire

Re: tail of two filaments

Post by BATTS »

Check the front brake light switch (I think Canada had these, UK didn't) its a poor design and has been known to stick on giving permanent brake light. Did you check the voltage at the rear light "plug" Brown is tail light, white is brake light and black and white is earth.
Chris
76 GT750, 78 GT550, BMW K1600gtl
User avatar
reginald

Re: tail of two filaments

Post by reginald »

Thanks Gents ,

I took the multi-meter out to test the rear light plug voltage. meter reading on battery shows 12.11v

But at the rear 3-pin plug connector , with the Ignition switched on but the engine not started , I get a Zero reading when connecting any pair of pins. Do i need the motor running to have voltage to test ?

I also discovered that if I switch the ignition key over to that 3rd 'empty' setting over to the right, it will light up the tail brightly like a running light, but brake light is still just a flicker. Thought I had discovered something so started the bike, and if i switch over to that '2pm' key position it immediately kills the engine. Dang!

what is this telling me .... I have Dirty Shorts ? How embarressing :shock:

Reginald
User avatar
canaletto5
Posts: 5228
Joined: Tue Jul 23, 2013 8:43 pm
Location: Derbyshire

Re: tail of two filaments

Post by canaletto5 »

The engine does not need to run to test the circuits. The battery needs to be fitted and the ignition on.

Check the three pin plug connection near the lamp assembly. Make sure that the three wires are matched on either side of the plug. White to white, brown to brown and black/white to black/white.

You will only get a voltage on the brown wire if the ignition is on position 2 and the light switch is on.This is your running light supply.

You will also get a voltage with the ignition in position 3 (Park)

Do this and check the voltage on the brown wire at the three pin plug. What is the reading?

To get a voltage on the white wire, (The brake light supply) you need to have the ignition on and a brake switch pressed. The light switch does not need to be on. What is the reading?

Obviously, on both tests, your multimeter negative probe has to be on a good earth. The black/white wire is an earth so you should use this for the test.

Kev
User avatar
reginald

Re: tail of two filaments

Post by reginald »

thanks for your support!

results this evening;
1) 3 -wire connector block has matching wire colours in correct pin-holes. Yippee.
2) earth + brown running light wire = 10.55 volts
3) earth + white brake light wire =10.82 volts
4) earth +brown wire , with key in position 3 (park light) = dunno, blew 20-amp fuse. I think ...I made contact with 2 pins, they are tiny and close together...shorted it out ?

5) replaced fuse, made another attempt at brown wire/key position 3, blew another fuse. Again it could have been me..but hmm I really was trying to be careful.
6) made clean contact , brown +key in position 3 = 12.41 volts
7) Battery reading =12.12 volts . I suppose I'm draining it a bit.
8) as before , I can light up each element separately, but with barely any brake "light".
9) I can start the bike and have a running light, but if I switch key to position 3, it kills the motor instantly. Would that be safety feature of a rear running light ? seems odd.
10) did i really blow the fuses twice, or is that a valuable clue to the Ghost in the Machine ?

thanks again,
Reginald Rear Lightless.
User avatar
canaletto5
Posts: 5228
Joined: Tue Jul 23, 2013 8:43 pm
Location: Derbyshire

Re: tail of two filaments

Post by canaletto5 »

The engine will go off in position 3. It is only there to light your rear running light (and small bulb in the headlight reflector in some countries). This is the Park position.

The voltages are really what you would expect under load except they seem to be the wrong way around? The brake light has higher wattage and therefore will drain more current, it should be giving a lower voltage reading than the running light because of that.

I think you need to take the light unit apart to see if there has been any funny business with the bulb holder. Check the black/white wire is prperly earthed to the unit. Then check that some-one hasn't accidentally reversed the soldered connections on the bulb holder itself. Don't ask me how I know this :oops:


The running light isn't supposed to be very bright (I know, there is a joke there somewhere) so that may be a clue.
User avatar
reginald

Re: tail of two filaments

Post by reginald »

Hey that just might reveal the funky factor right there.

so, it crosses my mind that since I powder-coated the steel rear fender, I might have inhibited a grounding path via the bolts and bare steel right there. Will dissect bulb ass'y first. then perhaps dremel off some bare contact spots under the fender where the mounting bolts live...?

Cheers,
Reginald, Dark Knight
Post Reply