Help Me Find My First Electrical Short

[ZacharyB]

For a GS750, '78...

Swapped out the R/R with an electrex and now I get a great charge to the battery, 14.8 volts through all RPM ranges. Everything seems fine. I was about to go for a celebratory ride when during my pre-ride check I pushed on the rear brake lever and the bike's lights dimmed dramatically for half a second (major current draw) then the bike died as the main fuse blew. I tried again with a new fuse... and it was blown in HALF!

I need my rear brake light, so I checked out my instruction manual's wiring diagram... Not much help, the two wires, white and orange, splice into quite a few things. I am wondering if I made some bad cuts splicing the Electrex R/R into the wiring harness.

I have the three yellow wires attached to the three alternator wires.

I have the ground wire sharing a ground with another wire at the right bolt of the starter relay.

I have the power wire sharing the positive battery post with the starter relay power wire.

I made an extra ground going from the R/R body to the battery negative terminal, sharing it with another ground wire and the battery negative cable.

I snipped and taped off the two useless terminals where the third phase (headlight circuit) was. I taped off the power lead-in to the wiring harness for the old rectifier as well.

I looked for torn wire insulation where I pulled or shoved the harness into and out of its little clips but couldn't find anything.

Do I have too many grounds connected to each other, or am I sharing power points that I should not?

I have pictures if it will help.

[earlfor]

Re: Help Me Find My First Electrical Short

Your R/R installation is exactly as the ones on my two bikes. I think youre ok there. Does the brake light operate normally when the front brake lever is pulled? If it does, the problem is not with the tailight bulb or the tailight bulb socket. Ground is common to both brakes, so if the front works and the rear does not, it is not a ground problem. The wire going to your rear brake switch is +, then makes continuity when the brake is depressed and the + continues to the lightbulb. I think you have a shorted wire between the rear brakelight switch and the lightbulb. There should be no connections to the wire between the switch output and the bulb, so I would first try just replacing that wire.

Earl

For a GS750, '78...

Swapped out the R/R with an electrex and now I get a great charge to the battery, 14.8 volts through all RPM ranges. Everything seems fine. I was about to go for a celebratory ride when during my pre-ride check I pushed on the rear brake lever and the bike's lights dimmed dramatically for half a second (major current draw) then the bike died as the main fuse blew. I tried again with a new fuse... and it was blown in HALF!

I need my rear brake light, so I checked out my instruction manual's wiring diagram... Not much help, the two wires, white and orange, splice into quite a few things. I am wondering if I made some bad cuts splicing the Electrex R/R into the wiring harness.

I have the three yellow wires attached to the three alternator wires.

I have the ground wire sharing a ground with another wire at the right bolt of the starter relay.

I have the power wire sharing the positive battery post with the starter relay power wire.

I made an extra ground going from the R/R body to the battery negative terminal, sharing it with another ground wire and the battery negative cable.

I snipped and taped off the two useless terminals where the third phase (headlight circuit) was. I taped off the power lead-in to the wiring harness for the old rectifier as well.

I looked for torn wire insulation where I pulled or shoved the harness into and out of its little clips but couldn't find anything.

Do I have too many grounds connected to each other, or am I sharing power points that I should not?

I have pictures if it will help.

[ZacharyB]

Ok, I'll check it out. The front brake light switch does not blow the fuse or dim the lights, it is solely the rear switch. (What a reaction it is, the fuse blows in 1 second with the rear brake depressed.) This'll be my first time going into a harness to check things out. I probably did something moving the harness around... Is electrical tape good enough to wrap it all back up again?

[earlfor]

Sure, you can use electrical tape to wrap any exposed wire. You shouldnt need to rip and tear into the main harness. There should be only one branch wire feeding the rear brake light switch and the output wire from the switch going to the brakelight bulb socket.

Earl

Ok, I'll check it out. The front brake light switch does not blow the fuse or dim the lights, it is solely the rear switch. (What a reaction it is, the fuse blows in 1 second with the rear brake depressed.) This'll be my first time going into a harness to check things out. I probably did something moving the harness around... Is electrical tape good enough to wrap it all back up again?

[Billy Ricks]

As Earl said, locate the rear switch and trace the wire back. It's grounding out against something. Could be one of the tabs that keep it from dangling or where it goes through the fender if it does.

[ZacharyB]

Strange

The problem is becoming either very complicated or remaining very simple. Here are recent developments.

Despite what you said, I opened up the harness and inspected the white wire (from rear brake light switch to brake light) carefully. There were no tears. It does not run directly to the light but of course splices in with the wire from the front brake light switch. I relocated an unknown ground from the battery negative terminal to where it was before, on the battery tray mount. I tried the rear brake again and the fuse stayed intact. I tried all my controls and still had power. Looks like it was time to ride...

My brakes were dragging, they need a good cleaning or a rebuild so I turned around to go home after getting gas. They were dragging pretty badly. When I came to a stop (using no brakes, no need), I stepped on the rear brake out of instinct and the bike died; the fuse had blown again. After going home and getting a screwdriver (none in my toolkit yet) I undid the rear brake light wire connection and put a new fuse in, then rode home.

I carefully inspected the wiring when it was out of the harness and there was nothing strange. I checked the rear brake lamp bulb and it was clean inside, as was its socket.

Any ideas? Should I unwrap the entire harness? I don't really want to, there is a cool original suzuki harness label on it.. :roll:

Thanks for any additional help or suggestions

[argonsagas]

A simple point....


You do NOT want 14.8 volts at all ranges.

One of the reasons you do NOT want that it that it will damage your battery, at the same time that it blows fuses.


First, look for the "Stator Papers" on this site. Follow the instructions for stator check with a multi-meter.


If things check out, as they may well do, you may find what you need is a new Regulator/ rectifier, as you are geting TOO MUCH voltage at the battery.

[Billy Ricks]

Just a thought here, you haven't mistaken a solid black wire as a ground have you? At least on my bike black wires are not grounds, only black wires with white tracers are ground wires.

[ZacharyB]

Just a thought here, you haven't mistaken a solid black wire as a ground have you? At least on my bike black wires are not grounds, only black wires with white tracers are ground wires.

Nope, I understood the difference when I noticed the two co-existing, like around my turn signals. I was thinking there might be a short in the rear brake switch itself since that has remained unchecked.

Per what argonsagas said, I'll recheck my voltage. My bike idles high (about 2000 sometimes after riding it for a while) and may be producing too much voltage at that point. The R/R is new, and Electrex, it couldn't have worn out unless it is a defective unit. It is wired direct to battery so it can't blow any fuses on its own. Unlike later bikes I have just one fuse to blow, the 15 amp main fuse.

But I find it peculiar the rear brake is the only one blowing the fuse. Does anyone know if these switches have a failure record?

One thing that might be it, my negative battery terminal wire is corroded on the inside. I was hesitating to replace it because it requires getting into the left side cover, which requires removing the oil. It might be next regardless, if you think that could be the case.

Thanks for your replies, they help me out

[Anonymous]

take your multi meter and check for continuity between both wires and the switch case after you disconect the switch. the correct answer should be no continuity. if there is then your switch is bad.

[ZacharyB]

take your multi meter and check for continuity between both wires and the switch case after you disconect the switch. the correct answer should be no continuity. if there is then your switch is bad.

Tried that yesterday but it checks out fine; no continuity open (relaxed), continuity closed (brake pedal depressed). It is as if a torn wire is jiggling around somewhere and by chance grounds out when the bike has been riding around. Unlucky episodes where the grounding coincides with me using the rear brake results in a short. Man, by now I wish it were a torn wire in the rear of the wiring harness :roll:

Edit: I should say I suggested a bad switch, wondering if something could come loose and roll around on the inside of it giving it intermittent shortings

[Anonymous]

if you are absolutely sure that it only blows the fuse when you press the rear brake, I would go ahead and replace the switch just for elimination purposes, then you also know your switch is fresh.
I think they are still fairly cheap, say less than a $20 bill

[ZacharyB]

if you are absolutely sure that it only blows the fuse when you press the rear brake, I would go ahead and replace the switch just for elimination purposes, then you also know your switch is fresh.
I think they are still fairly cheap, say less than a $20 bill

Too bad I spent all my money on the bike itself, it is becoming a bad habit with every vehicle I buy

Maybe my father will help me out.

Do you mean direct from Suzuki, or from one of the aftermarket places like oldbikebarn.com or partsnmoreonline.com?

[Billy Ricks]

I don't think I would suspect the switch since it is basically all plastic. Try pulling the plug off the switch and hotwiring it to see if the short still happens that way. At least you can eliminate or confirm the switch as the cause.

[ZacharyB]

I don't think I would suspect the switch since it is basically all plastic. Try pulling the plug off the switch and hotwiring it to see if the short still happens that way. At least you can eliminate or confirm the switch as the cause.

Because the problem is already intermittent it might not do anything, but I'll give it a shot. Thanks