blown main fuse (intermittent)

[bob d.]

I have a 1981 GS550t that blows the main fuse somewhat randomly. One instance has occurred twice now: I ride for about half an hour, stop for five minutes, fire it back up and then the fuse blows. The battery drained once on me but seems to be holding its charge now. I've looked all over for a short but no luck so far. Any suggestions/recommendations? First bike. Thanks.

[tas850g]

someone recently just had that same problem. The culprit was a wire shorting out on the handle bars in the right control switch. Coming from the either the on/off switch or the starter button. Take that off and take a look if you haven't yet. Check the wires coming from the ignition switch that go into the headlight bucket too. Time to check out a wiring diagram.

[rustybronco]

R/R might be going bad.

If you haven't changed the regulator/rectifier by now, it might be a good time to replace it and clean up ALL the charging system connections.

[bob d.]

i already looked into the right handlebar control and everything looked good. i also checked the headlight fixture and found no obvious shorts. i didn't check from the headlight to the handlebar though. i'll do that. thanks.

[tas850g]

Most posts here lean toward an electrical short. The hard part is finding it.

[SqDancerLynn1]

The fact that the battery went dead sugests the regulator/rect

[rustybronco]

...........

[tas850g]

how would that blow the main fuse? ok, after thinking about it i can see how. Many different things you need to rule out i guess.

[rustybronco]

An internally shorted (or intermittently shorting) R/R will blow the main fuse.

The R/R is connected to the negative side of the battery (frame) and supplies the power from the stator, through the main fuse, to the battery.

when the positive side of the R/R shorts to the negative side (or draws to much current), poof goes the fuse.

***EDIT*** completely charge the battery, completely disconnect the R/R (all four wires) ride it around and then see if it blows the fuse under the same conditions as before.

[salty_monk]

Wrong Info MR TAS That was my skunk with the shorted hand controls & it wasn't blowing the main fuse ONLY the ignition fuse. (Bottom 10amp one on the block).

Dan

[tas850g]

one of the reasons why the negative side needs to be grounded well? Can the negative side of the r/r short to the positive side?

[tas850g]

sorry dan, i thought you were blowing the main fuse. my mistake.

[rustybronco]

My good friend Tas,
the reason the negative side needs to be properly connected (grounded) to the negative side of the battery (and the positive properly connected also), is so that the current supplied to the battery is the maximum that can be delivered to the battery, as it is needed, with no losses.
It is also necessary to do this, in order for the R/R to be able to correctly read battery voltage (through no voltage drops, positive or negative), to properly regulate charging system voltage.

Can the negative side of the r/r short to the positive side?

yes, it can short pos to neg internally.

[bob d.]

thanks rusty. that info cleared up a number of questions.

[tas850g]

i love reading these posts b/c i learn sooo much. Thanks Dale.