Hitchcocks Forum

I'm getting a 1970 350 Bullet running again after many years of being off the road and the wiring vandals have attatcked it over the years in India so I have had to rewire it. All is good except the blinker indicator globe. I have never had my head around how this works. This has been fitted with an aftermarket setup but I think it is similar in principle to the later Bullets. Single filament globe, wires from each front indicator are joined at the globe fitting, which also has a negative wire treminal.Only way I think they whould work is to have a diode in each wire so that they don't backfeed, but I have never seen diodes in any wiring on other Bullets. Any thoughts?

Hi Norm, seems to defy logic doesnt it but sure no diodes are involved. Secret lies in that earth (minus) connection, one of those that we always say to check when odd things are happening to indicators/brake lights, all coming on at once sort of thing. once the power has reached the two wires at the warning lamp it has a choice.... (trying to make this simplistic norm) 1 is to go through the low watt bulb element, then away home to the battery through the big earth wire, whilst some of it will attempt to go back through the other two high wattage bulbs giving high resistance to the run back to the battery. Power takes the easiest route. There will be some backfeed but would it be enough to light both front and back bulbs (globes) probably not as its only flashed on for part of a second anyway.........
To test the theory dissconnect the minus earth wire from the warning light and see what happens to all four indicators. Maybe talkin bollocks but sure Les will explain.... gwilly

Thanks Gwilly, there is something strange with the setup, this works fine on the right hand but not the left, had a similar problem with my crossbred a couple of years ago when I fitted LED indicator lights to the casquete, right worked fine but I had to fit another globe inside the casquete to increase the load so the left would work. I'll try your idea and let you know

Hi Norm & Gwilly. It took me a couple of reads and this is what I think you have Norm? You are saying the blinker's warning (speedo)light is fed by both left and right blinkers and the warning light also has an earth. If so, all that is wrong is that the warning light should NOT be connected to earth. The warning light should be cross connected (In series) across both L & R live feeds to the blinkers which allows the warning light to work by "seeing" the earth via the very low resistance of the other sides bulbs. All four blinker lights complete their circuit through an earth connection. As the the warning light is very low wattage, it means it also has quite a high resistance, so the current through it is limited and is in the order of only about 1/4 of an amp. The blinker lamps are fairly powerful high wattage lamps and their cold resistance is very low (the resistance rises considerably when fully lit by the correct voltage) So, even though current of one side is cross connected through the warning light to the opposite side's blinker bulbs the current is to low it does not illuminate them and the resistance of the blinker bulbs (in parallel)is low enough to let the warning light illuminate nearly to full brilliance. This action works either way from L to R or R to L. So all you have to do Norm is check that the warning light is driven by both live sides of each sides blinkers...& remove any earth from the warning light bulb holder...it needs to be insulated from earth. SO gwilly is right with his description. Hope I've understood your problem, otherwise I've wasted my time or should it be?

BTW. the reason the LED didn't work is in the name of the device...Light emitting DIODE.... a diode is a rectifier and only work one way round. LEDS require a dropper resister to limit the current through them to about 25mA...and a different wiring arrangement..... You would have needed two diodes to drive the LED and the dropper resistance in series with the LED down to ground....it would have worked OK then.

Thanks Les,
You could be right but it was wired with the earth connected so I assumed it worked, although nothing much else did, I'll give it a try and if not I will fit a diode in each feed wire.The existing wiring was such a mess I am unable to even see if they had fitted diodes in it
Thsnks again

If the warning lamp is a filament type, you will NOT require diodes...... you will only need diodes if the warning lamp is an LED (+ dropper resistor of about 400 Ohms down to earth)

Thanks Les, you got it again, works fine, no idea how it worked originally, just have to make sure the bulb holder is properly insulated. thanks again