78 gs400 fuse blowing while riding

[Brendan W]

Overheating at the end of a fuse is usually bad contact allowing micro-arcing.
The glass fuses, especially the cheap types, can have a crack in the solder joining the fuse wire to the inside of the cap.

[angrypants]

hi all,
i haven't had time to really get stuck into this yet, i've just moved house so much of the last two weekends have been unpacking and finally last sunday setting up the garage.. i finished the garage sunday arvo and had a while to "fiddle" ( i really have no idea what i'm doing with electrics).
anyway my first hope was dashed ...that it would have miraculously disappear .

i noticed
- the fuse ends get hot without the bike running when 1. i put the lights on high and low ,2 put the blinkers on (both sides). NOT when i put either brake on. i didnt let it get get so hot to blow the fuse though but i imagine it would if i left it. is it nowmal to get too hot to hold after 10 seconds? is that an indication of a short
Can i discount the regulator & the rectifier being the problem now?

i tried the horn but didnt have it on for long naturally so cant say much about that

at one point when aimlessly "fiddling" the bike would not start, i mean nothing at the starter, not even a click from the relay.( the inition lights , neutral light were on blinker lights would work ) i wiggled stuff around and pressed horn and then i suddenly got power to the starter. fuse then blew after a 20 seconds at choke idle.

oK so i'm a bit OCD when it come sto doing work on the bike i like to read things many times and have an idea of what i'm doing before i start -- otherwise i put things off ( like my tank sealing , its spooked me worrying about damaging the paint of doing a crap job -- i put that off for 9 months after buying the kit lol.. it was easy in the end). i feel that same hesitation / fear now with this electric issue.

Ok do i have the process correct
1. first call is to clean all connections and switches and ensure all the grounds are good -- i have bought some deoxitd 100s, and i have the dielectric grease.
2. possibly at the same time as 1. disconnect the likely things, test and see if problem persists
3. check the touching points of the harness for wear and exposed wire
4. start at one end and work all the way through the harness

OPk now how exactly do i test ?
- steve mentioned use a voltmeter rather than waiting for fuzes to blow... how does one do that ? do i hook that up to either side of the fuse terminals and look for something? ? then what? im guessing i only touch the terminal to test or i will i burn wires / kill my multimeter.. can you please elaborate steve where do i connect it what do i look for

- as for disconnecting stuff, eliminating causes ? am i just removing bulbs for the lights, or disconnecting the wires that go to the bulbs, ( to prove the issue is not between the battery and the lamp and then reconnecting that wire and then disconnecting the other side to see if the issue is in the lamp fitting ?i imagine i'm doing this with that light in the on position?

- with disconnecting / checking switches what do i do there ? do the same as above?



oh as for testing the ignition switch? how does one do that ? as i can see how i can disconnect that and still have current running through the wires ?


sorry to sound so naive.. its very possible i have read so many different things that i have confused the hell out of myself

thanks i really do appreciate all help

grant

[pete]

Don't have much time for a proper response this morning but a couple of quick things...

No the fuse most definitely shouldn't get hot like that! And without the bike running, yes that sounds like your R/R is not the culprit at this point in time.

To test the ignition switch, the best way is actually with a multimeter, and check the voltage at the battery compared with the voltage coming back out of the switch connector. In my case when I did that initially I was losing something like 2.5V which is huge.

That, however, won't cause your fuse to be hot, that would cause the ignition switch to get a bit warm potentially, but the main issue will be less voltage to your coils etc.

[angrypants]

Don't have much time for a proper response this morning but a couple of quick things...

No the fuse most definitely shouldn't get hot like that! And without the bike running, yes that sounds like your R/R is not the culprit at this point in time.

To test the ignition switch, the best way is actually with a multimeter, and check the voltage at the battery compared with the voltage coming back out of the switch connector. In my case when I did that initially I was losing something like 2.5V which is huge.

That, however, won't cause your fuse to be hot, that would cause the ignition switch to get a bit warm potentially, but the main issue will be less voltage to your coils etc.

thanks Pete

[angrypants]

Went out this morning to start hunting found the battery almost dead
there is power going trough the fuse even without the key in
is that normal ?
i has a test light to each end of fuse connections goes brighter with key at on positions and then even brighter in park - normal ?

Ive put the battery on charge and will look through the wiring harness for wear today and go back tonight to use the multi meter and test light

[Steve]

i noticed
- the fuse ends get hot without the bike running when 1. i put the lights on high and low , ...

Are you switching between HIGH and LOW, or have you found a way to put them both on at the same time?
If you are putting them on at the same time, ... DON'T. The extra current will tend to blow fuses.

Went out this morning to start hunting found the battery almost dead
there is power going trough the fuse even without the key in
is that normal ?
i has a test light to each end of fuse connections goes brighter with key at on positions and then even brighter in park - normal ?

A couple of things to note here:
1. You should not have a meter or test light connected unless you are actively using them. Digital meters don't draw a lot of power, but analog meters do, and so do test lights.
2. Don't use the PARK position when parking the bike. That turns on the tail light, which is probably why your battery is dead.

.

[angrypants]

Hi Steve
i was using the switch on the bars for high and low -- I don't think both were on at same time
As for the test light I only had it on the fuse connections while I cycled through the key positions only a few seconds
I then disconnected the head light put a fuse in and tried to start the bike and it turned the starter but weakly ... stopped then took the battery out to charge it and it was at the lower two LEDs end of the charger lights when connected
I've never used the park position ... maybe starting it multiple times over the last few weeks and not actually having it run for more than a few seconds has drained the battery??

Nothing further to report had to run off to official at a local golf match after this mornings checking with the rest light

[angrypants]

Ps here is the wiring diagram for the bike ... it was asked for earlier in the thread 22E8800E-6D2A-4ACD-9518-2F388812E40D.jpg

[angrypants]

quick update,
found it
finally got some time to have a good poke around, i started at the front and worked back, disconnect the horn, the headlight, the head light, blinkers, the handle bar brake switch and the instruments and cleaned with deoxit every connection as i went ... got up to location of the reg etc the rubber boot there houses many connections, opened it up and it was very dusty a red connection showed signs of burning and had melted a bit of a white blue wire next to it.

still blew a fuse after parting them, So disconnected the stator wires to the regulator and also the rectifier and no blown fuse.

just had dinner and now going out to attend to the last of the connections, chase the red wire for damage in the harness and do some charging testing etc

thanks for your help so far

[Chuck78]

Pardon me if this is re-hash, but I only have a quick moment to comment, and thus I have not read the long thread above...

Disconnect all grounds and light bulbs, etc - any normal continuous path to ground, and start unplugging things and checking for continuity to ground. if something has continuity to ground and it shouldn't, THERE is a suspected cuplrit. Also if you are testing the entire harness as you unplug one thing at a time, when you no longer have continuity to ground, the last thing you unplugged is suspect.

Also I find that the ignition switch plastic plugs in the headlight buckets become very brittle and crumble often on GS's. Modifying the electrical system to run an ignition relay and headlight relay with power straight from a fused line to the battery positive takes the strain off of the ignition switch (and kill switch).

Is the bike overcharging when running? What is the battery voltage with the bike idling, and revving to 4000rpm, 5500rpm, and 8000-ish rpm all separately?

The first work I do to a GS aside from get it running, is to replace the old regulator-rectifier with a Shindengen 4012941 "SH-775__" series unit used out of a Polaris ATV/UTV SxS and test the stator really well, with a visual inspection of the stator windings if possible to see if it looks burnt, even if it tests okay for resistance and output (while running the engine solely off of the battery with stator unhooked measuring AC voltage between the 3 wires in all combinations). I rewire to a single point ground, and I rewire the power distribution slightly from stock (and abandon the 3rd stator wire that goes to & from the headlight switch as a 2-wire loop to disconnect the 3rd stator phase when headlight is off) as Jim aka POSPLAYR has detailed many times. Adding fusing differently. Then I add an ignition relay and dedicated fused hot wire from the battery to the power terminal of the relay, and use the old ignition coil power wire to switch the relay on and off, and then a new ground wire for the other relay-trigger-coil wire terminal on the relay. NO (normally open) terminal is off when ignition is off, this feeds the ignition coils and Dyna-S aftermarket ignition or OEM electronic ignition power source.

Then I go through the entire harness and inspect every connection. poor connections will strain things severely and cause thing to burn up. Pull the tank, seat, and headlight to access most of the bike's wiring, and inspect and clean EVERYTHING thoroughly.

If you do all of this, surely you will have a healthy electrical system and find the source of the short.

[Chuck78]

So you can run the bike off the battery with the stator unhooked, and it NO LONGER BLOWS FUSES?

Sounds like your stator or regulator-rectifier may be the issue.

Do an ohm test to the stator legs unhooked from the R-R, should be somewhere around 1.8 or 2.3 ohms if I recall (please look this up) between all possible combinations of measuring 2 each out of the three wires. Do the same test on AC voltage on your multimeter, with the bike running off the battery, stator unhooked, measuring stator output. Refer to the GS Resources "The Stator Pages" for AC voltage values. If this checks out good, hook it up again. Stat bike, test whole charging system voltage at battery with bike running. Should be 12.3 or 12.7 idling, up to no more than 14.6 or so when revving to higher rpm's. Should be a constant increase with no dead spots, and then it should peak out in the 14's and never go higher even when (warmed up engine first please! do not rev high cold!) you rev it to redline, should never go over 14.# volts. 14.9 is even a bit high but NEVER should go into the 15's or higher. Regulator-Rectifier is bad if it goes higher, or if stator output checks out good but DC voltage out of R-R is low (could have a very/faulty dead battery or something else grounding out and sucking the juice out of the charging system nonstop also).

[pete]

Have you still got the stock original glass fuse on it? They're notoriously bad, and you're much better of replacing it with an inline weatherproof blade holder from Supercheap or wherever.

I've had three situations on my 450 that have caused a blown main fuse, and incidentally these all happened with blade fuses as I swapped the glass fuse holder out many moons ago:

- Overheated fuse due to corrosion in the fuse holder, fuse had obvious signs of almost melting by the time it blew.
- Faulty battery that caused it to blow once RPM's got up enough for the stator to generate enough voltage, obviously with the coils' current draw the total with charging exceeded 15 amps.
- One fuse holder leg had worn/expanded so the fuse was loose in the holder.

quick update,
found it
finally got some time to have a good poke around, i started at the front and worked back, disconnect the horn, the headlight, the head light, blinkers, the handle bar brake switch and the instruments and cleaned with deoxit every connection as i went ... got up to location of the reg etc the rubber boot there houses many connections, opened it up and it was very dusty a red connection showed signs of burning and had melted a bit of a white blue wire next to it.

still blew a fuse after parting them, So disconnected the stator wires to the regulator and also the rectifier and no blown fuse.

just had dinner and now going out to attend to the last of the connections, chase the red wire for damage in the harness and do some charging testing etc

thanks for your help so far

Just had to include my earlier post

Sounds a lot like the second issue I had where a faulty battery caused more than 15 amps charging voltage and was blowing the main fuse.

I notice you mentioned a low battery in a previous post. How old is the battery? Is it a lead acid type? Have you kept the acid levels topped up? That was my issue, the levels kept dropping due to where the exhaust runs on my 450 which I wasn't aware of at the time (battery since relocated). Funnily enough the battery was still capable of cranking the bike etc.

Just mentioning the above again in case you can't find an issue with the R/R and end up still scratching your head. The only way I could verify it was the battery was fortunately having a spare on hand as I had a brand new one ready for my Katana.

[Chuck78]

My one friend who has a kickstart GS550... he bought it with a bad battery, but it would hold a charge for several hours, BUT the battery was draining the charging system output soooo badly by spring (bought in December), that the thing would not really even run for more than 20 seconds...
bought another, did not winterize it, lead acid battery, guess what? rode fine that season, the next season after no indoor heated storage and no trickle charger, this new battery was roached, and was causing such a severe drain on the system that the bike would barely run. I gave him another worn out battery, would not have enough juice to electric start it, but he had been kick starting it the entire time when he was having battery issues anyway, no money for new batteries, and after a while, this weak battery had such a bad charging system drain or nearly a direct short with no charge-holding capacity, that he came to me and said "my turn signals stopped working, and the bike runs rough sometimes" - which really meant that the thing had almost no voltage when running with this bad battery as it was sucking it all out of the charging system. running with no battery would have let it run better!

You can try that, kickstart it or bump/push start it (take off running next to the bike pushing it in neutral, hop on, and pop the shifter up in 2nd immediately with clutch pulled in, and let clutch out somewhat gradually. Do this until you get the speed and/or clutch release technique to get it to start. Or just get it running, and remove the battery CAREFULLY live, tape off battery cable end, and take it for a ride and see if it blows the fuse.

[angrypants]

Hi guys thanks for the input
i thought I posted again last night after I hit the garage after dinner
Earlier I did go through and disconnect lights horn brake switch , I truments etc and still blew fuses it runs fine when I disconnect the red out of the rectifier

i tested the stator all tests in the list except the charging one where I connect to battery and stator leg at 5000 rpm as the fuse blows when revved.
I did the first 3 on the flow chart
the ohms test was 0.9 or was it 1.2?? It was late - either way all the same- pass
the ground test OL - nil reading pass
the volts coming out of each leg at 5000 rpm was just under 80 for all -pass

as it has a seperate reg and rec I did the diode test on the rectifier red out and the 3 " yellows " going in ( red is the one that had a burnt connector in the boot). Two legs were 0.7v and the other one OL / nothing
could that be the problem ?

from the stator the three legs split and 3 go to the reg and 3 go to the rectifier. Nothing but a ground comes out of the regulator ... and red and a ground out of the rec.( there is no direct to the head light I think ) I am yet to chase the red where it enters the harness ..... I think then direct to the fuse which then goes to the starter relay where it meets a direct from the battery. The direct from the battery splits before the starter relay and into harness

i have thoroughly cleaned all connections and all the grounds ... except the one where the rec grounds onto itself..the attaching bolt goes through it's middle of the rec and the screw faces down vertically and its head was made of cheese even with good jis screw drivers it hcewed up, the angle wasnt flush though due to the chain guard, but i risked it and faile dlol .... I'll have to drill that out unless I can take the mounting panel off if that is the case on thsi bike like my makes gsx250

So if this all means the rec is stuffed what do I replace it (and the old regulator) with ?
I have sh775aa that was for my gs1000 if I ever get to it and the sh775aa is huge - should I swap the old gs1000 rec/reg into the gs400 its much smaller than the sh775? It might fit in there ? Or do I just go an 80s rr off a 250 or 400 as I read in the stator papers the smaller CC bikes don't really have these issues. Or is the 1000 rr not the right one to use. getting another sh775aa wil cost me over a hundred aussie dollars

ill get onto the preferred grounding method too when i swap this out

learning lots I think .. I hope ��

[Chuck78]

figure out where you can fit in an sh775, they are a bit big, but I always get crafty and squeeze them on to the smaller GS550's I work on for friends...
And get one of the plug kits exactly like this for Shindengen RR's, Rick's or RM stator sells them for like 13 or 14 dollars all over eBay, but I can't for the life of me type in the right description to bring up those listings:

https://www.ebay.com/itm/283501981486