Triumphrat

robot1 · 08-21-2007, 11:30 PM

Hello out there!

After years of admiring Brit bikes from afar, I made the plunge and got myself a 1976 Bonneville. The bike is in great shape, but seem to have come across a problem with the electrical system.

Basically, I can turn the headlight on. I can turn the turn indicators on. I cannot do both. I've looked through the Haynes guide, the owners handbook and the OzBloke guide to Meriden electrical systems. Looking at the wiring diagrams, the two systems seem completely independent.

Has anyone else experienced this, or is this some modification unique to my bike's history?

I'd appreciate any advice as I step boldly into the wonderful world of Lucas electrics.

GrandPaulZ · 08-21-2007, 11:37 PM

Welcome. I can almost guarantee you have a weak or missing path to ground on either the headlight, the turn signal circuits, or both.

Loose connections are the biggest problem in Lucas electrics.

That '76 Bonnie is a relatively limited edition bike, HANG ON TO IT.

Welcome to the forum, and welcome to the wonderful world of good old British Iron!

KADUTZ · 08-22-2007, 01:39 AM

sounds like the turn signals are tied into the headlite switch

OzBloke · 08-22-2007, 03:11 AM

robot1,
When you say you can't do both:

- if you got the headlight off, do the indicators flash on/off
- if you've got the headlight on, then turn the indicators on, what happens to the headlight - does it dim down? do the indicators come on but not flash?
- if you've got the indicators flashing, and then turn the headlight on, to the indicatoprs stop flashing and go on solid, or go off?
- with indicators off, and headlight on, do the indicators glow weakly (check at the rear)
- is the engine running while you're checking the lights / indicators?
- how's your battery voltage?

The answers to these questions will point is in the right direction to find the fault.

Pete

robot1 · 08-22-2007, 11:39 AM

Thanks for the quick responses.

OzBloke -- I'm at work now, so I can only relate what I have looked at so far, but I'll update tonight.
1) with the headlight off, the indicators flash on/off. (seems slow, but like I said this is my
first experience with British bikes)
2) with the headlight on, and I turn on the blinkers, I haven't noticed a dimming in the
headlight (noticed is key, I'll look closer tonight). The indicators do not come on at
all
3) with the indicators on, and I turn on the headlight, the indicators turn off (not solid, off)
4) haven't checked for a glow with the headlights on and the indicators off
5) for most checks, the engine was off. However, I have had the engine on to just check
and see if I even got a weak light from the indicators with the headlight on --
nothing. She's not really idling right now, so I'll need to enlist help to check 4) with
the engine running.
6) Haven't checked the voltage yet. Yeah, I guess that would be good to check. It's
on the list for tonight.

KADUTZ -- I agree that it sounds like that, but why and how? I've been looking over the wiring diagrams,
hoping to find something besides the battery that they are both tied to, but they seem to be (at least
originally) fairly independent circuit.

GrandPaulZ -- Unless of course, there is a ground short/open. Definitely worth looking into.

OzBloke · 08-22-2007, 08:12 PM

Robot1,
From you latest post, I'd agree with Kadutz that the standard wiring has been altered, and the indicators are somehow connected to the lighting switch. I can't really understand why someone would do this intentionally.

I'm at work now, so I'll look up the wiring diagram tonight, and let you know what colour wires you should be looking for in the headlight shell. It's probably the wire that is supposed to go to the blinker can from the ignition switch, now routed to the lighting switch.

fominoz · 08-22-2007, 11:39 PM

Another option could be that maybe the headlight is a converted H4 with 55/65W that is drawing way too much power so the indicators do not work - happened to me.
That said, this only happened on either batery only or when ideling - if the revs were up, both headlight and indicator worked as more juice was coming from the alternator.
fom

OzBloke · 08-23-2007, 12:19 AM

Fom,

That's the reason I asked robot1 to check if the indicators came on solid, and if the headlight dimmed, with both switched on at the same time. The way the indicators work, they need current flowing before the circuit is cut by the flasher can. With the indicators drawing 3.5 amps and the headlight 4.5 - 5 amps, if they're both working in parallel, you'll certainly see a dip in brightness if the battery is low. Similar symptoms can be seen with poor earthing.

As you correctly describe, if the battery is low, with headlight on and indicators turned on, the indicator lamps will glow (not full brightness) and stay on solid for a fair while. This means there's not enough current flowing to heat the bimetal strip in the flasher can to bend it enough to open the circuit.

From robot1's observations regarding the indicators not coming on at all with the headlight on, it is very likely that the indicators are wired (incorrectly) via the lighting switch, where power is applied to either the headlight OR the indicators, but never the two together.

fominoz · 08-23-2007, 03:08 AM

OzBloke,

well, then that is me having to check the wiring on my bike as well as i assumed the reason on mine was the fact that i went from the sealed beam to the H4 light.

I replaced the stock 'standard' H4 60/55W with a H4 35/35W and that seems to have solved the issue with the indicators on my bike (which did not work at all, i.e. no glowing or anything with the H4 60/55W)

but after i re-read your post again it seems to be more an issue with the wiring rather than the power consumption of the H4...?

HughBromley · 08-23-2007, 09:50 AM

My bike has a similar current problem:
I've just bought a TR65 Thunderbird 650 from 1982 and had a similar problem.
I rode it home from Scotland 350 miles in the rain with the headlight on (at a steady 60-70mph), with hindsight the battery was discharging. First the indicators stopped working, the headlight got dimmer and dimmer then the bike stopped all together.

The new battery goes in tonight and I will check for charging and also for the correct wattage headlight.

This thread was useful, thanks