Big thanks to member "ohgood" for the headlight interrupt instructions. Attached are some updated instructions with pictures. I just picked up a 1999 GS500 that is really hard to start cold and I have drained my battery twice so far on cold mornings. This mod momentarily kills the headlight when pressing the starter button freeing up extra amps/voltage for the starter motor. Every little bit of voltage helps on those cold mornings.
Parts I used to wire in the relay:
One relay from Advance Auto Parts. I bought the following relay. It is Optronics brand. model A-715A. 40A 4 pin 12v relay.


Four female connectors
One wire tap
one male connector for wire tap

Step1-remove headlight by unscrewing the two phillips screws underneath the headlamp housing
Step2-Disconnect the bulb and set the lamp aside
Step3-Cut the black/white ground wire that runs to the headlight bulb connector about haly way up (see picture). Strip both sides and add a female connector to each. Then plug the bulb connector side into 30 pin. plug bike harness side into 87a pin.


Step4-find the unused brown wire inside the housing. I used this as the ground wire and wired this into terminal pin 86
i used a wire tap and a male connector.



Step5-find the yellow/green wire that skips over the big yellow connector (there were two on my bike). see my finger pointing to the wire I used for power. You need to tap into one side as this is power for the relay into terminal 85. i just trimmed a piece of wire and stuck it into the existing connector and secured with extra electrical tape.




Step6-reconnect headlamp
Step7-turn key on and start bike. the headlight should momentarily cut out when the starter button is pushed.
Step8-reinstall headlight and enjoy more cranking amps when starting your GS

If it doesnt cut out when starting then you did something wrong. recheck all of your wire taps/connectors/powerwire into 85 (yellow/green stripe)/ground wire into 86 (brown wire)/ bulb connector ground interrupt into 30 and 87A (black/white wire).

I hope the pics help.
~j

Be nice to resize the pictures. Try for no more than 1000 pixels wide. 800 is about ideal.

Not sure what the pictures are they're so BIG.

2006+ bikes have headlight cut off with starter button.
I did one for Trey using a waterproof relay. Suppose I should post it someday. It is easy to install.

Just be careful that you don't actually treat the brown wire as a "ground".  It is powered 12-14V when the key is in "ON" or "PARK". 

Adidas:  Did you use a relay like the one above, or a normally closed one?

I used a SPDT relay, using the normally closed contact for the headlight. Starter button energizes the relay thus opening the headlight contact. Better that way. If there is a failure to the relay coil and it doesn't energize, you still have headlights.

I run the headlight ground through the relay as it comes off the headlight. Then I have the ground for the coil, too. Add one wire from the starter button and you're done. I'll draw it up. Clever design and really simple to install.

One contact and one side of the coil go to ground. Other contact goes to the ground wire of the headlight. Add wire from starter button to other side of coil. 3 wires is all that are required.

Bugger. All that trouble just to start a bike?
I just press the off switch when starting cold

American bikes do not have a switch for the headlight. Law says headlight must always be on.

Quote from: adidasguy on May 01, 2012, 08:15:07 PM
American bikes do not have a switch for the headlight. Law says headlight must always be on.

That is also the law for australian bikes!!
I have no idea why mine has one?
Maybe europeon import? Dunno

Switch says off-park-headlight 3 position

Depends on when the law took effect. You have an 89? Maybe the law took effect after 1989 or they continued to sell bikes with the switch for a while.

Quote from: adidasguy on May 02, 2012, 12:51:55 AM
Depends on when the law took effect. You have an 89? Maybe the law took effect after 1989 or they continued to sell bikes with the switch for a while.

Maybe?
None of the other bikes I have ever come across have had them so I dunno?
Never seen it before this one.

Quote from: codajastal on May 02, 2012, 12:50:23 AM

Quote from: adidasguy on May 01, 2012, 08:15:07 PM
American bikes do not have a switch for the headlight. Law says headlight must always be on.

That is also the law for australian bikes!!
I have no idea why mine has one?
Maybe europeon import? Dunno

Switch says off-park-headlight 3 position

Headlights always on hasn't been a requirement on australian bikes for quite a few years. It was removed in ADRs version 3(or maybe 2 not sure but it is gone).
Might have been retained in one of the sets of various state laws, in which case manufacturers would just make one version for the entire country. Or they just never changed after it was removed from ADRs.

Edited the picture sizes and links with Picasa.