Dim taillight Q?

[Don R]

81 GS1100, has a new battery, 12.6V engine off, key off, good charging, SH775 V reg upgrade so the voltage supply is good, the issue is a dim taillight bulb. With the engine off, the 1157 bulb is only getting 6 to 7 volts at the plug in, the single element bulb is getting a little over 8 and is brighter. For now, I popped in an old LED bulb which isn't normally an improvement, but in this case it works better. The LED causes the burned-out light sensors in the dash to illuminate, a regular bulb does not. Do I need to clean every connection and the key switch or is there a component that might cause it? I also tried a 2057 bulb with no improvement.

[tom203]

Work on checking the grounding of the taillight assembly…..for a quick check, run a jumper wire from battery negative to taillight and see if things get brighter.

[Rijko]

Good thing you discovered the low voltage issue.
This is a well-known issue on these old bikes unfortunately.

Which likely means you have issues with low voltage in many places.
Connectors, switches ... which may cause all sorts of problems like melted connectors
and wires, R/R blowing up, or the igniter, ignition stops working, etc.

So i recommend checking voltage, cleaning connections, etc.
Hopefully in time to prevent costly repairs.

[Don R]

The old rectifier/regulator connections were nasty, I cut them off and used new 4mm bullet connectors. I'll start again at the fuse box, I've already added a battery to frame ground, it wouldn't hurt to loop it to the taillight also. Thanks for the ideas.

[Cipher]

The old rectifier/regulator connections were nasty, I cut them off and used new 4mm bullet connectors. I'll start again at the fuse box, I've already added a battery to frame ground, it wouldn't hurt to loop it to the taillight also. Thanks for the ideas.

Its a pain but you would do well to check the ignition switch itself. I was doing a lot of work on my bike years ago and decided to check all connection and found that the contacts in the switch had degraded to crumbling verdigris. It was shocking current could flow through. Fiddled a bit and the things crumbled to dust.
Arizona harness from ebay that I had bought in a misc. grabbag sale saved my season and the bike.

[Don R]

Thanks for the heads-up on the switch. At a glance, they look a lot like Honda switches of the same era, I can't help but wonder if they were made by the same supplier? I did find oem switches still in the wild (parts stores) but they run close to $200. I need a ride on it today to keep my enthusiasm going.
I fixed an 850 Yamaha once that wouldn't start by replacing the fuse block with a blade type aftermarket one. The voltage drop was so bad the ignitor didn't work. I sold it to two guys that came, grabbed it, handed me cash and took off like the cops were chasing them. They even left a box of parts because they didn't have time to grab them. Since the Yamaha, this is the first bike newer than 78 that I've messed with due to the wiring complexity.

[Cipher]

Thanks for the heads-up on the switch. At a glance, they look a lot like Honda switches of the same era, I can't help but wonder if they were made by the same supplier? I did find oem switches still in the wild (parts stores) but they run close to $200. I need a ride on it today to keep my enthusiasm going.
I fixed an 850 Yamaha once that wouldn't start by replacing the fuse block with a blade type aftermarket one. The voltage drop was so bad the ignitor didn't work. I sold it to two guys that came, grabbed it, handed me cash and took off like the cops were chasing them. They even left a box of parts because they didn't have time to grab them. Since the Yamaha, this is the first bike newer than 78 that I've messed with due to the wiring complexity.

Nippon Seiki speedo/tach is on every big four manufactured bike that I have seen.
a lot of parts are outsourced. Japan Inc is a beauty.
'amazon has switch gear for cheap.

[salty_monk]

The ignition switch is the chief culprit if the voltage is low in other places too....

You can put a relay in the system using the ignition wire as the trigger for a workaround.

[Redman]

GS1100E...?
GS1100G....?

I suspect 1100E, because of the mention of the tail light and the single filimant light.

Does 1100E key have a "park" position. G does, and there are contacts and wiring only for the tail light.

[Don R]

Sorry, it is an EX. I'm going to ride it a bit before I get my feathers ruffled, After a long retirement it might need a break-in again. I rode it a few times today and really liked it, there is a pulsation in the front brake, a few things were ridiculously over-tightened so I may re-torque the rotor bolts and see if that helps.
I did relays on my GL1000 Honda so I am familiar with them. It had low ignition voltage that I think affected the Dyna that is on it. It has gl1500 coils and no ballast resistor also.

[Don R]

Here is what I probably did wrong, I cleaned up a bunch of corroded, soldered, taped and gooped connectors where the old voltage regulator was. I installed an SH775 and connected to the 3 existing yellow wires with new 4mm bullet connectors, I also ran the red and black directly to the battery.
I realized today I have a light green, red male end and a red/white female end loose in the wiring cover that may have formerly been wired to the old V. Reg.
The Haynes manual is showing red/white and a green/white feeding the right control from the old V/reg. and the red also connected to the stock V. reg. What should I do with these now? From what I'm seeing, maybe feed the two dead wires with the one that's hot? What is odd is, everything works but the lights have low voltage, I wonder if they are back feeding from elsewhere?

[Grimly]

Those two wires up / from the right switch were for switching the third phase in and out when the headlight is on. On US bikes of later vintage where the headlight is mandatory, the connection was permanent.
All you do with the now spare pair is ignore them, as you're running your headlight all the time anyway.

The red from the harness that used to go the old reg is now your feed point for the output of the 775. You can carry on with the direct connection to the battery if you wish - there are pros and cons to either method. Just tape up the open red end to prevent any shorts.

[Big T]

Here is what I probably did wrong, I cleaned up a bunch of corroded, soldered, taped and gooped connectors where the old voltage regulator was. I installed an SH775 and connected to the 3 existing yellow wires with new 4mm bullet connectors, I also ran the red and black directly to the battery.
I realized today I have a light green, red male end and a red/white female end loose in the wiring cover that may have formerly been wired to the old V. Reg.
The Haynes manual is showing red/white and a green/white feeding the right control from the old V/reg. and the red also connected to the stock V. reg. What should I do with these now? From what I'm seeing, maybe feed the two dead wires with the one that's hot? What is odd is, everything works but the lights have low voltage, I wonder if they are back feeding from elsewhere?

All GS models use the same basic path. Battery, main fuse, ignition switch, other fuses, their respective circuits.
Yes, I know some only have one fuse.
So, test the red wire from the ignition switch for 12 V, then work your way downstream to the tail light

[Don R]

Thanks, that clears up my confusion a little. I've converted a bike or two to the parking lamp, euro type headlight and found the wiring already there. It makes sense that this bike would also have left-over wires and yet still operate properly.

[salty_monk]

Make sure there is no rust or corrosion on the back of the rotors or at the wheel... It can hold the rotor off slightly & create the pulse. That interface should not be painted.

Other than that a pulse could be either a caliper not releasing properly or a warped rotor.