Topic: Feel like trouble shooting blown fuse?

[socalsupermoto]

Symptoms: intermittent 15amp fuse blown, main fuse under left side cover. 3 x now when riding/running the brights, anywhere from 10-30 min after running bike. I've just been carrying a big pile of fuses to get home.

Recent changes/stuff i coulda screwed up:
1) handlebar change, so coulda screwed up anything in the bucket although everything works and seemed to match up well. there's alot of black, is it possible to connect to the wrong ground?

2) converted to h4 bulb. bulb is "super white" probably around 50 watts. works well, just don't know if it's drawing too much and blowing the fuse?

[cobra2411]

Try wiggling the harness to check for an intermittent short. Also you could get a ammeter and check the amperage that you're running. The stock bike runs about 7 amps so I can't see you being too high.

[TwoTired]

Well, I guess it is an SOHC4 of some type.

The typical problem is oxidation (can be transparent) on the fuse clips.  Pass current throught the resistance generates heat, which melts the fuse near the end cap.  If the fuse is melting there, the fuse holder is the problem.

The stock 15 A fuse normally passes about 10-11 amps for the stock bike and stock 40/50 W headlight.

Every 12 watts added to the headlight consumption adds another 1 amp to the main fuse load.
The mechanism for fuse blowing is heat generated by current passing through it.  So, a fuse running at 2/3 of its rating will run warm, but won't burn your thumb.  The closer to it's rating it operates, the warmer it gets.
With extra power running through it AND fuse clip oxidation the fuse holder plastic can melt, which causes alignment and contact reduction for replacement fuses (leading to more heat build up).

So, if your fuse clip contacts haven't been polished bright and shiny, and your fuse still runs too hot to hold your thumb on after 10 minutes of operation, and it "blows" under the end caps.  It's your fuse holder.

If the fuse is blowing near it's center point, you probably have some sort of wiring short.

Cheers,

[socalsupermoto]

Well, I guess it is an SOHC4 of some type.

The typical problem is oxidation (can be transparent) on the fuse clips.  Pass current throught the resistance generates heat, which melts the fuse near the end cap.  If the fuse is melting there, the fuse holder is the problem.

The stock 15 A fuse normally passes about 10-11 amps for the stock bike and stock 40/50 W headlight.

Every 12 watts added to the headlight consumption adds another 1 amp to the main fuse load.
The mechanism for fuse blowing is heat generated by current passing through it.  So, a fuse running at 2/3 of its rating will run warm, but won't burn your thumb.  The closer to it's rating it operates, the warmer it gets.
With extra power running through it AND fuse clip oxidation the fuse holder plastic can melt, which causes alignment and contact reduction for replacement fuses (leading to more heat build up).

So, if your fuse clip contacts haven't been polished bright and shiny, and your fuse still runs too hot to hold your thumb on after 10 minutes of operation, and it "blows" under the end caps.  It's your fuse holder.

If the fuse is blowing near it's center point, you probably have some sort of wiring short.

Cheers,

sorry, k2 cb750. the fuse is blowing right in the middle, and is hot as hell. i've got a volt meter but little electronic know how, where would I measure amperage from and what would i set the volt meter to?

meanwhile I'll take another look at the bucket, tape up anthing that looks exposed (like the wires coming off the turn signal bolt , that was a new one).

I forgot to mention I also removed that annoying turn signal beeper thing, maybe there's a culprit there?

[cobra2411]

The wire coming off the turn signal bolts are grounds...

The buzzer shouldn't be the problem.

TwoTired  +1

Check the fuse holder and clean.

[Gaither]

TT

You're always there to help - and we do appreciate you. My fuses were blowing at the end BEFORE you told me to clean 'em. Thanks!    Great bunch of folks here!

Socal, you said your fuses were blown in the middle. You may have another problem. However, If the fuse clips haven't been cleaned in a while, it is still a GOOD idea to clean 'em - even if they look pretty good. You'll find a .22 cal bore brush works perfectly.

The same is true for all of your poly enclosed elec connectors - and pack 'em with some dielectric grease. These things worked wonders for my 550.

I HATE WIRING!

Good luck with your problem







 

[socalsupermoto]

thanks guys. I'm gonna start by cleaning the fuse holder, although to culprit is probably something i screwed up in the handlebar change/wiring. I'll take another look in the bucket and post up the findings. would have done it by now but i've been going to the track/working a ton this week.

should I flip the headlight connector to disengage the highbeam for a while to see if that makes a difference?

[thehammer]

try replacing the fuse holders with microfuse type holders from radioshack. they work real good and its way easier to find replacement fuses. especially the 7.5 amp one.

[1974CB750rider]

Where is the ignition switch mounted? The reason I'm asking is because when mine was doing what yours was doing it turned out to be that little metal collar around the ignition switch that hold the wires together. It was grounding out on something metal and would pop the fuse right in the middle.

[socalsupermoto]

Key switch is in stock location under the tank, left side. I'll play with wiggling the bars and seeing if anything comes in contact. If I run out of fuses I'll try the radiishack holder, great suggestions!

I still think most likely I screwed up something in the bucket since that's the last thing I did before fuses started popping

[1974CB750rider]

Just remebered something. In the bucket there is a brown wire that does not seem to go anywhere. At least on my bike there is. Everything on my bike works but the brown wire doesn't seem to have a place. It is a hot wire and will blow the fuse if it grounds out.

[socalsupermoto]

Just remebered something. In the bucket there is a brown wire that does not seem to go anywhere. At least on my bike there is. Everything on my bike works but the brown wire doesn't seem to have a place. It is a hot wire and will blow the fuse if it grounds out.

i remembered that wire, it's exactly what i was worried about so I went to take a look. mine was brown with a blue stripe. i had already taped it up. I couldn't find any exposed wire in the bucket, other than the grounds coming off the signals

I played with the ignition. I tried intentionally trying to get it to ground out by crossing metal between it and the fame, with no luck.

I checked the fuse box. it looks shiny and clean. no build up there. maybe with a new fuse box it'll run cooler in combo with the beefier headlight per tt's suggestion

can anything in the right control cause a blown fuse? after the bar swap wires are a little crowded there, nothing major though. i tried wiggling the crap out of that, and couldn't get the fuse to blow. so i figured that's ok. maybe i'll try whipping the bars from side to side to see if that can make the fuse blow.

On a hunch I disconected the wire going to the brights and rode around, no blown fuse.

Any other suggestions? My current plan is to ride around without too much load (ie the brights) and see if all works out ok. if the fuse blows I might undo my handlebar job to see if some of those not so smooth holes i cut/drilled cut a wire somewhere? If no fuse blows I'll just assume it was due to too much load from the headlight.