Suzuki gp100 6 volt electrics

stevenc370 · Two Stroke Sniffer Joined: 17 Oct 2014 Karma :

Got my little suzuki running after 12 years in storage problem lies with the rear light. The tail light and brake light both work independently but not together so when the tail light is on when I press the brake switch the lights dim rather than brighten up any ideas anyone??

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

As far as I'm aware, the brake light and tail light on a GP100 ought to run off entirely seperate and independant circuits.

The head and tail light run on an AC direct lighting circuit (so they only run when the engine is on and brighten as you rev it).

The brake light runs off a DC powered circuit from the battery.

So, if they both work properly in isolation (bright tail light with engine running. Bright stop light with and without the engine running), the only place the two circuits SHOULD meet is at the earth connection.

I'd therefore suspect a bad earth. Japanese bikes of that era have notoriously badly earthed taillight clusters. FInd the earth connection (often a mucky ring terminal trapped under the rusty bolt holding the corroded rear mudguard to the rotting subframe spar) and give it a damned good clean so you have shiny metal of the terminal contacting shiny metal of the frame.

Also check out the earths on the bulb holder.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
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davebike · World Chat Champion Joined: 15 Nov 2013 Karma :

Probable poor earth connection or poorly fitting bulb
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stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

It occurrs to me that a defective rectifier could also cause similar symptoms. If that were the case, the indicators and horn wouldn't work.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

DrSnoosnoo · World Chat Champion Joined: 28 Mar 2012 Karma :

I add to the above comments, earth.

My CG was a 6 volter and the lights improved a lot when I went through replacing totally rotten terminals at the rear.
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stevenc370 · Two Stroke Sniffer Joined: 17 Oct 2014 Karma :

Ah well I have removed the battery. I didn't know it ran off a dc circuit. I going to run a live from the ac lighting circuit to the top of the brake light switch see if I can set it going. I'm going for the cafe racer look so didn't really want a battery.Hopefully it will work

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

stevenc370 · Two Stroke Sniffer Joined: 17 Oct 2014 Karma :

Right what do you think to taking the live from the battery charging circuit straight to the brake light switch. This live has the rectifier on it to change over to dc so should power the light it's essentially the same circuit just without a battery in between could possibly put a resistor in there to take up what voltage would have been used in the battery