GS850 Perpetual blown fuse

[Dougv]

Hi all, I?m new to the group having found you while searching for a solution to my challenge?
My bike (GS850 1986 model) has developed an electrical issue that has progressively got worse and is foxing me.
Coming back from a ride-out last weekend, the indicator/neutral light/gear shift/ indicator/horn fuse blew. I replaced it when back home. On my secondly jolly the fuse went again but lasted about 20 mins before doing so. Third fuse change saw it last less than 5 mins. Fourth with the seat and panels off was when I revved it. Fifth and subsequently is whenever the bike is turned on. All other fuses are fine.
I took the indicator relay off as I initially suspected it was due the indicator circuit and when I turned the bike on, low and behold the fuse didn?t blow. As such I started by replacing the relay with a new one. Turned the bike on with the new relay? fuse blew instantly.
Now, I?m aware that some models have an indicator self-cancelling unit. As far as I?m aware, my doesn?t as I cannot find it on my bike (nor, if I have got one, has it ever worked in the 6 years I?ve had the bike!) as such I?m hoping someone here might be able to guide me.
Any ideas please?

 

[cowboyup3371]

Did you already check to see if you may have any wiring with broken insulation touching the frame anywhere?

 

[Dougv]

Hi cowboyup,
Thanks for your reply and yes, I've been through the bike. I'd recently (a fortnight ago) replaced the head gasket so had a fair amount of the bike apart. It ran fine for the first 200 miles but has started playing up since last weekend. I've checked all wiring and connectors but no luck there.

 

[Brendan W]

Do you have a three or two pin relay?
Three is for the TSCU, two means someone may have junked or ignored the controller. It's about the size of a pack of cigarettes and usually lived on the battery box. Has a big tail with about half dozen wires. Mine is off the bike and I run a two pin relay.
If the fuse blows after connecting the relay with the signals OFF, the problem could be a short in the supply to/from the handlebar switch.
The switch has a plug under the tank. The harness ties under there were metal and many corrode and the harness drops onto the top of the motor and plugs melt. For starters I would check out that plug and see if the fuse stays intact with it open and work on forwards to the switch.

 

[Steve]

Especially since you had the engine apart, I would check the horn wire(s). :-k

The horns have two terminals. One is always hot with the key ON. If the insulation is compromised, it can easily short out.

Regarding your self-cancelling signals: look at the switch on the left handgrip. Does it have the word "AUTO" next to it? If the lettering is worn off, activate the switch in either direction and notice the operation. If you DO have self-cancelling signals, there will be FIVE positions of the switch.

Starting at the far left:
1. Activates the left signal and starts the timing cycle for the auto-cancel. Is spring-loaded to go to position #2.
2. Maintains left signal operation for the duration of the timing cycle.
3. Manually cancels operation from either side.
4. Maintains right signal operation for the duration of the timing cycle.
5. Activates the right signal and starts the timing cycle for the auto-cancel. Is spring-loaded to go to position #4.

The "timing cycle" that determines signal duration is operation of the bike at a speed over 10 MPH for more than 10 seconds. It can be extended at any time by pressing the switch to position #1 or #5 as necessary. Many are frustrated by the length of the cycle. For a lane change, it seems to last too long, giving you about 10 flashes at road speed. When approaching an intersection for a right turn, it does not seem to last long enough and has to be restarted. A minor inconvenience.

All of this assumes that you still have stock components in working order. A previous owner may have changed it, possibly thinking it was not working, when it really was.

.

 

[Dougv]

Hi Brendan and thank you for your guidance.
To confirm, yes I have a three pin relay.
You've mentioned a unit on the battery box. I will look to disconnect this unit and see what happens although I had mistakenly assumed the unit you'd identified (to the right of the rectifier in the image below) was the ignitor unit.



I let you know how I get on later today once I'm back home.
Once again, thank you.

 

[Dougv]

Thank you Steve.
I shall give this a good look later today and see what I can discover.

Especially since you had the engine apart, I would check the horn wire(s). :-k

The horns have two terminals. One is always hot with the key ON. If the insulation is compromised, it can easily short out.

Regarding your self-cancelling signals: look at the switch on the left handgrip. Does it have the word "AUTO" next to it? If the lettering is worn off, activate the switch in either direction and notice the operation. If you DO have self-cancelling signals, there will be FIVE positions of the switch.

Starting at the far left:
1. Activates the left signal and starts the timing cycle for the auto-cancel. Is spring-loaded to go to position #2.
2. Maintains left signal operation for the duration of the timing cycle.
3. Manually cancels operation from either side.
4. Maintains right signal operation for the duration of the timing cycle.
5. Activates the right signal and starts the timing cycle for the auto-cancel. Is spring-loaded to go to position #4.

The "timing cycle" that determines signal duration is operation of the bike at a speed over 10 MPH for more than 10 seconds. It can be extended at any time by pressing the switch to position #1 or #5 as necessary. Many are frustrated by the length of the cycle. For a lane change, it seems to last too long, giving you about 10 flashes at road speed. When approaching an intersection for a right turn, it does not seem to last long enough and has to be restarted. A minor inconvenience.

All of this assumes that you still have stock components in working order. A previous owner may have changed it, possibly thinking it was not working, when it really was.

.

 

[bobgroger]

As Steve said, take a good look at the horns. My 850 had an intermittent short that would blow the fuse. One of the horns was rotated a bit and the horn hot terminal was touching the frame bracket once in a while.

 

[Steve]

That unit to the right of the R/R is likely the ignitor, as you suspect, but take a look on the other side of the battery box.

.

 

[Redman]

An other vote for checking horns as cause of blowing fuse randomly.

Sometimes a horn can have an internal problem that causes it to short power to the ground-frame. And let me repeat, this does not reguire you to push the horn button.
As others have said, in some fashion or other, the horn has power on it all time (when ignition switch on). (THe button completes the circuit to the ground.)

Look at the wiring on the horns.
THe org/grn wire(s) at the horn is right from the fuse. Look to see if might be shorting to frame somewhere. As a test of any internal problem in the horns, disconnect them from the horns, maybe tape up. See how long you go without blowing fuse.
The Grn wire goes to the horn button. If that wire shorted to frame it would not blow a fuse, it would make the horn sound, same as pushing the button.

 

[Grimly]

The first mysterious fuse-blowing episode on a GS850 of mine was the wiring harness where it touches the steering neck. Time and mileage/vibrations had taken their toll on the insulation, just out of sight of a normal inspection. I've since made a point of wrapping the harness with spiral wrap in vulnerable areas.

 

[Dougv]

The first mysterious fuse-blowing episode on a GS850 of mine was the wiring harness where it touches the steering neck. Time and mileage/vibrations had taken their toll on the insulation, just out of sight of a normal inspection. I've since made a point of wrapping the harness with spiral wrap in vulnerable areas.

It would seem you were spot on Grimly!
Having worked my way around the bikes wiring harness, it would seem the problem was just as you'd suggested.
Thank you to everyone that offered their thoughts and advice... all very much appreciated.

 

[Redman]

..... ..................
Having worked my way around the bikes wiring harness, it would seem the problem was just as you'd suggested.
...........

What did you observe? What did you find? How did you find it??