What is this block called and what does it do?


Information and questions on GL1800 Goldwings (2001-2017)
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TimSenior
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Motorcycle: 2003 GL 1800 Previously 1998 Goldwing 1500 SE

What is this block called and what does it do?

Post by TimSenior »



Hi, I recently acquired a very low mileage 2003 GL1800. Some of the saddlebag and trunk LED molding lights weren't working so I removed them and installed a new Big Bike Parts LED light kits. It appears to me that the old LED's that were on it were an older Big Bikes Parts light kit that a prior owner installed. Tied into the wiring harness at the back of the bike, behind the panel the license plate is attached to, is a sealed black rectangular block with wires going in on one end and wires coming out on the other end. The words "Big Bike Parts" are written on the block. (See the attached picture) Can someone tell me what this block is called and what exactly it does? It's clearly part of the old LED light kit that is obviously not needed for the new lights I installed. Also, while working on the lights, I inadvertently created a short in the right trunk turn signal circuit and fried a fuse. After replacing the fuse, the right turn signal on the trunk no longer works. I've determined that the wire that provides power to the turn signal socket goes through that block. There is power to the wire going into the block but not coming out. It appears that the short may have damaged whatever is in that block as well. I connected a jumper bypassing the block and the turn signal started working. But when I do that, the brake light on that side of the trunk quits working. I'd like to eliminate the block but it's not obvious looking at it how that should be done. Any ideas, thoughts or suggestions would be greatly appreciated. Thanks!
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Rambozo
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Re: What is this block called and what does it do?

Post by Rambozo »

Possibly a light converter. Usually used with a trailer hookup to convert independent lights into common lights.
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Andy Cote
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Re: What is this block called and what does it do?

Post by Andy Cote »

Could also be a trailer harness isolator. Looks like a bank of relays.
2015 Goldwing, basic black

Previously: GL1200 standard, GL1200 Interstate, GL1500 Goldwing, GL1500 Valkyrie Standard, 2000 Valkyrie Interstate, many other Hondas
TimSenior
Posts: 7
Joined: Sat Aug 26, 2023 9:38 pm
Location: Medical Lake, Washington
Motorcycle: 2003 GL 1800 Previously 1998 Goldwing 1500 SE

Re: What is this block called and what does it do?

Post by TimSenior »

Thanks, I'll look into that possibility. The bike does have a trailer hitch but no trailer light connector. These are the LED's I took off the bike.
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TimSenior
Posts: 7
Joined: Sat Aug 26, 2023 9:38 pm
Location: Medical Lake, Washington
Motorcycle: 2003 GL 1800 Previously 1998 Goldwing 1500 SE

Re: What is this block called and what does it do?

Post by TimSenior »

Upon further research, I believe the block is in fact a relay isolator. Because of the way it is wired into the lights circuit, and because there are no wires connecting to a trailer light plug, it appears to me that it was installed as part of the Big Bike Parts LED light kit to isolate the LED's from the trunk and saddlebags lights. Unfortunately it's probably in the area of 20 years old so finding a replacement is unlikely. Understanding what it is and what it does however should help me to figure out how to eliminate it and restore the wiring to its original state. Thanks again for the help!
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Re: What is this block called and what does it do?

Post by WingAdmin »

It's definitely a trailer isolator, I put almost the identical one into my GL1500. I believe it's a Show Chrome unit.
TimSenior
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Joined: Sat Aug 26, 2023 9:38 pm
Location: Medical Lake, Washington
Motorcycle: 2003 GL 1800 Previously 1998 Goldwing 1500 SE

Re: What is this block called and what does it do?

Post by TimSenior »

Upon further inspection of the relay isolator and associated wiring, I was able to yard it all out and return that part of the wiring harness to its original configuration. Doing so resulted in the elimination of the turn signal function of the trunk light assembly. The taillight and brake functions of those assemblies still work correctly. With the absence of a trailer plug attached to the isolator wiring, and the presence of splitters going to the trunk light assemblies but not the saddlebag light assemblies, I'm left to conclude that the isolator harness was installed to give the trunk light assemblies turn signal capabilities, and to power the LED lights in the mirrors. The old trunk and saddlebag LED's were spliced into factory wiring, not the isolator harness. I'm not completely sure, but I don't think my bike was originally equipped with turn signals in the trunk light assemblies. The turn signal lights/horn wiring diagram in my service manual only shows two turn signal bulbs at the back of the bike and two in the front. As it stands, everything is now working as intended, including my new LED's, so all is well that ends well. Time to ride!
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Andy Cote
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Re: What is this block called and what does it do?

Post by Andy Cote »

I think you got it. One amber lens and one red lens in each saddlebag light; each with one bulb. Trunk lights are all red, no turn signals and usually two bulbs on each side.
2015 Goldwing, basic black

Previously: GL1200 standard, GL1200 Interstate, GL1500 Goldwing, GL1500 Valkyrie Standard, 2000 Valkyrie Interstate, many other Hondas
TimSenior
Posts: 7
Joined: Sat Aug 26, 2023 9:38 pm
Location: Medical Lake, Washington
Motorcycle: 2003 GL 1800 Previously 1998 Goldwing 1500 SE

Re: What is this block called and what does it do?

Post by TimSenior »

Someone changed the lenses on this one, the turn signal lens is clear. I'm not sure that is even legal where I live here in Washington State.
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Andy Cote
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Re: What is this block called and what does it do?

Post by Andy Cote »

TimSenior wrote: Thu Aug 31, 2023 8:28 pm Someone changed the lenses on this one, the turn signal lens is clear. I'm not sure that is even legal where I live here in Washington State.
Honda changed the amber lens to clear starting in 2006 (I think) with amber bulbs. Perfectly legal as long as the bulb is correct.

There were also some early LED conversions that replaced the entire light rather than just the bulb. They had clear lenes as well. Easily recognizable looking through the lens or seeing that the bulbs can not be removed from the back.
2015 Goldwing, basic black

Previously: GL1200 standard, GL1200 Interstate, GL1500 Goldwing, GL1500 Valkyrie Standard, 2000 Valkyrie Interstate, many other Hondas
TimSenior
Posts: 7
Joined: Sat Aug 26, 2023 9:38 pm
Location: Medical Lake, Washington
Motorcycle: 2003 GL 1800 Previously 1998 Goldwing 1500 SE

Re: What is this block called and what does it do?

Post by TimSenior »

Gotcha, thanks for the clarification. I guess I'll have to try to find some amber bulbs.


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