Gold Wing 1800's are notorious for speedometers that run about 5% high. As I like to have an accurate speedometer, I chose to install a Yellow Box (www.blackrobotics.com) speedometer correction unit WITHOUT cutting and splicing into the wiring harness.
My solution was to build my own wiring harness that I inserted in between a factory wiring harness connector located behind the right air vent. Below are the steps I took to install it:
I removed the right side trim strip, the right glove box and the cover which holds the glove box key along with the bottom three ALLEN bolts which gave me a bit more flexibility in working with connectors and finally the air vent. The connector is located behind the air vent and one does not need to remove the top shelter to do this installation; however, it is a bit difficult and patience is your friend. I perservered and finally located the white 3 wire connector (#1 pin has white with black stripe from the speed sensor, #2 pin is green (ground) and #3 (brown) is power. The connector was very hard to disconnect, but fortunately I have small hands. Attached is a picture of the connector on the wire that leads to the speed sensor.
I then cut a couple of short pieces of jumper wire and connected the RED from the YB to the BROWN jumper and affixed the appropriate terminal ends. The BLACK from the YB was connected to the GREEN ground wire. The WHITE from the YB was affixed to a pin on the Speed Sensor connector that I built. The GREY YB wire was affixed to the connector leading to the speedometer unit. All connections were soldered including the wire to pin connections. Below is a photo of the completed harness.
I then connected my new harness (which was duly wrapped with wiring loom protection. It really was hard to connect the upper connector as there is very little room. I ended up using a small section of baling wire with a hook on the end to provide resistance to be able to press the connection together. Connecting the lower connector was a breeze. I then threaded the wire loom up to an area just in front of the glove box and zip tied the YB to the wiring loom along with the jumper plug that would be needed in the event of failure of the YB <which I never expect to happen>. Below is a picture of it in its final resting place.
My initial correction is 5% which makes the speedometer accurate. I wish the YB came with the jumper harness premade as it would be so simple to build at the factory.
While doing the project I found an unused 12v plug which I'm now going to use to wire a power plug in my right fairing pocket. It's found in the wiring group that's just behind the glove box key switch. The plug is reddish brown in color. I'll do that project sometime in the future which will include lengthening the accessory plug wire and drilling a large hole in the pocket.
The above was originally posted on the gl1800Riders.com message board, but I thought it might have some applicability and inspiration for someone who's Pashnit about motorcycles.