Need help from electrical gurus w/intermittent short blowing ignition fuse

[aussie_king_mick]

This is an old mechanics “trick” to diagnose a short to earth in vehicles or motorcycles etc….it works well therefore I recommend that you give it a try:
http://www.crookedriverwriter.com/index.php?/Automotive-Topics/the-old-headlight-trick.html

[Midnightventure]

I like that.

[NoTraffic]

I just had a similar issue with a Suzuki SV650. I had a short somewhere that kept blowing a 15A signal fuse. Like you, I had gone through about 10 replacement fuses and reproducing different scenarios that would keep me frustrated (blew when put just to "on", blows after 10 minutes, blows after I hit brakes, etc).

After resolving it just yesterday, here is what I would do differently (take about 2-3 days to do this):

1) Remove all fairings, seats, passenger seats - anything that could possibly have a wire behind it.

2) Trace the wires that are leading to the blown fuse. Take off all loom, electrical tape, and start inspecting it. When you go through one section, call that "Done". (I found some suspect wiring which contained pools of water, so just untaping it does you some good).

3) Look at nearby fuse placements that may be coupled or linked to that starter fuse as well. Trace those wires. If you traced all the visible wires, consider yourself halfway done. It is NOW a wire that you cannot see which is shorting/grounding and is usually touching a ground. Trace all metal components and look for a hard to reach wire. This is usually the cause of the short.


This is what I did with my SV and finally found a hard to reach harness under the tail section that was completely out of sight and one which I would have never guessed to cause a short. It's only when I started to trace every fathomable piece of electrical wiring that I found this to the culprit.

Good luck, just takes some patience and persistence. I almost threw in the towel too.

[Grinnin]

Originally Posted by niided

Looking at the schematics , could a bad rectifier or ignition module cause a short to the
#3 fuse? How about the coil? By the description I provided, it seems to be that it is most likely a wire to ground causing a major short.

Rectifier -- not all that likely; Ignition module -- more likely.

The one diagram that I looked at showed the wire from that fuse going directly to the ignition unit. Wires branch from there to several locations (tachometer, coils, ground, diodes and onward to safety switches).

There's the ugly possibility that there's a short inside the ignition unit itself. Probably too pricey to buy on pure speculation and hard to find someone who will lend you theirs.

When working with a dodgy ignition on an older bike, I made a bunch of short wire jumpers. Each jumper was a 2" wire with a male spade on one end and female on the other. If you did the same with several inline fuse holders with 5A fuses in each, you could identify where the current is going.