Suggestions to find electrical gremlin

The brale lights and horn fuse on my 2001 748 started to blow out. It does not happen immediately after I replace the fuse, but at some poibt it does. So I have to check for shorts somewhere.

Any suggestions on how to do this?
Any obvious places to check?
Do I need a multimeter to do this?

Thanks in advance.





Modified by Alex at 8:58 PM 2/20/2005

Yes you need a multimeter.
Pull the fuse that is poping. Check to see which side of the fuse does NOT have power. This is the side of the wire that has a short in it. Now put your multimeter to resistance. Check the resistance of this wire in reference to ground. If it is shorted you will see it. Sounds to me like you have a scuff in a wire and when something moves just right it shorts out. So you will have to play with the harness or wiggle the suspecting wires while measuring the resistance. It can be frustrating and time consuming, but you will find it.
The first thing I would check is the wiring under the seat going to the tail light. Then I would check the wiring at the base of the bulb.

CuSTOm hit the nail on the head, and welcome to the wonderful world of wire casing

I haven't found it yet. And another fuse is blown.
Electrical problems are a PITA.

CuStOm:

Just to clarify what you said.
1)If I pull the fuse, one side (the one not connected to the battery) will not have power (with ignition ON) regardless of whether there's a short on that side. Or am I missing something?
2)If I put the MM to resistance and all is good, I should see zero resistance along the tested line and if there's a short I should see high resistance or off scale. Correct?

The wiring under the seat tested OK using the method in 2) above. So did the rear brake switch line (rear brake connector detached). So did the rear brake connector to fuse line and the rear brake connector to underseat wiring line. That tells me that the problem may be b/w the front brake switch and the fuse.

have you found a patten when the fuse blows? like when you hit the brakes, or horn? will the fuse blow if you let the bike set with the Ignition on for a while or dose the ike have to be running? or do you have to be riding the bike?

Mike996,

That's the most frustrating part. The fuse won't blow with the ignition ON and the motor not running. I can engage both brakes and all will be fine. But it blows when I ride. That make finding the troble spot hard, I think.
When I checked the rear brake circuit, I wiggled all the wires and connectors and there was zero resistance across the entire circuit.

After I check the front and horn circuits, I think I'll disconnect one circuit at the time (rear, front, horn), ride, and see which circuit cause a fuse to blow. I got a bunch of 7.5 A fuses now.

Yep. that sucks. You mite want to get a wire schematic, or I could draw out the circuit you're have issues with and post it on here if you need it.

I have the circuit schematic, but thanks for the offer.

When you ride, your weight may be crushing a wire and causing the short. It sounds like an intermittent problem, you may want to disable all the parts but one, (no lights just horn) and add them back one by one until it blows the fuse. This is another way to at least narrow it down.

This probably won't help you but maybe it'll stimulate a thought: I had an enigmatic situation where flashing my high beam - after no work/monkeying/problems/etc, out of the clear blue this began - would blow the headlight fuse, no matter if running or just in ON postn.

Checked the bulb, was fine, swapped with buddy's bulb and it worked, no more blowing. THEN, replaced my original bulb and now the problem is gone. WTH?! I cleaned the contacts prior to this pt, checked connxns, all that...nothing evidently amiss.

Just one of those wierd things...

Hey, I think this exact same thing happened on my brothers 748.

With his, it was the wire that came from the brake switch on the handlebar that went down the steering head. It was getting pinched when you turn the handlebars all the way to the stop and shorting out. As soon as he fixed up that section of wire and made sure it wasn't getting pinched, it never happened again.

Similar problem as above..... wire harness on the left side of the steering tube was getting pinched. Wore the the covering and shorting out against the frame. Took me awhile to find that one.......

I'm with the others on something getting pinched. My suzuki's head/tail lights were shorting at seemingly random pts. Went through a dozen fuses until (by now it was dark which was a blessing in disguise) I turned the bars and saw a blue spark down past the triples where a bundle of wires ran.

A nearly indiscernible spot was worn through, contacting a bracket causing the short. Fixed it and I was good to go.

I found it!! Thank you all, especially JamesP, TK, and doocatiboy.

You pointed me in the right direction. The line from the front brake switch to the horn connectors was pinched between the lower triple and the headlight bucket when turning the handlebars left all the way to the stop. With time the outside insulation broke and so did the insulation on one of the wires. The wire would then short against the frame and blow the fuse. But all was OK when the wire was not touching the frame.
I wrapped the wires with electrical tape where they were pinched and then wrapped the outside with more tape.

It all makes sense now. I've been doing a lot of hard braking practices on a deserted road with lots of U-turns between practices.

Thanks again for saving me a ton of time and aggravation. It would have been very hard to find this by just checking the circuit without pinching the wire in just the right way. But seeing it made it all clear.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Alex &raquo;</TD></TR><TR><TD CLASS="quote">I found it!! Thank you all, especially JamesP, TK, and doocatiboy.

You pointed me in the right direction. The line from the front brake switch to the horn connectors was pinched between the lower triple and the headlight bucket when turning the handlebars left all the way to the stop. With time the outside insulation broke and so did the insulation on one of the wires. The wire would then short against the frame and blow the fuse. But all was OK when the wire was not touching the frame.
I wrapped the wires with electrical tape where they were pinched and then wrapped the outside with more tape.

It all makes sense now. I've been doing a lot of hard braking practices on a deserted road with lots of U-turns between practices.

Thanks again for saving me a ton of time and aggravation. It would have been very hard to find this by just checking the circuit without pinching the wire in just the right way. But seeing it made it all clear.

</TD></TR></TABLE>


I love speedzilla, and I love the search function. I am currently having the EXACT same problem with my 748 and was about to really tear into this thing but now I know what Im going to check first!!!


Thanks everyone, and sorry for bumping a real old thread I'm just excited.