weird amperage draw

[jonr]

Had a strange encounter with my usually reliable 78 GS750 this last week. I start up the bike and all lights start to flicker on the bike and the engine cuts in and out. I keep it going with a bit of extra gas and wiggle various wiring harnesses on the bike to no avail. So, I let off the throttle and it dies. All lights go out and the ol girl is dead.

So, obviously there was a short. I check my only fuse first and it is blown to shreds. This fuse is not that old either. I put a new 15A fuse in and turn on the key. I get out my multimeter and check the amperage from the positive battery lead to the output side of the fuse holder and I get about 2.8A! WTF? My headlight is off (I "fixed" the switch long ago) and I know the ignition does not pull 2.8A! By chance, I put my fingers on the fuse holder and it was warm! Huh? I relocate my leads to either side of the fuse holder and it reads 2.5A. All connections are corrosion-free too.

I'm thinking to myself, "how can fuse holder pull 2.5A? I replace it with a new holder and I only measure 300mA with no headlight and the ignition live. That's more like it!

Where in the hell did the gremlins in the fuse holder come from? Partially broken wires inside the insulation?

The bike runs fine again with the new holder, but does anyone have a clue about this bizzaro fuse holder? Maybe the original flicker was arcing between two sides of a partially broken wire in the holder? That might explain the heat too. But why the extra 2.5A? How could there be a partial short in just that part of the hot wire that feeds my whole bike?

Sorry for the long post!

J

[jimcor]

In today's 'Mysteries of the Universe'.

In line fuse holder, Jon? I replaced one of those ( it replaces a bad main fuse connection in my fuse box) this year. For no reason that I could fathom the darn thing would lose continuity every now and then. Plenty of spring tension, clean connections, new fuse, all OK. Wasn't worth fooling with. No idea why it would do this. Got a new one and everything is fine.

[jonr]

Jim,

Yes, it was an inline fuse holder. I bought a heavy duty one and crimped on some new bullet connectors and in she went in with no problem. I've been thinking about it and it must have been broken wires inside the insulation. All the connecting surfaces were clean and shiny and when I checked resistance on the line, it only measured .03 ohms. So, at least a few of the strands must have been ok to produce that kind of reading and heat up when only 2.8A were passing through it.

J

[rek]

Yep, we have 30 y/o bikes and sometimes wierd probs. i work with 30 y/o
aircraft and sometimes the samething happens, turns out to be a connection corroded or corrosion wicked up in the wire causing high and very variable resistance. sounds like you troubleshot it and got out of the way.
WTG.

[Planecrazy]

Just for kicks and grins you should consider replacing THAT inline fuse holder with one of the newer blade type holders ... the quality of the contact between the fuse and the leads is by far superior to the older style...

My .02
Steve 8)

[Anonymous]

Is there a difference between the "mini" and "normal"-type blade fuses (other than form factor)?

[Planecrazy]

Is there a difference between the "mini" and "normal"-type blade fuses (other than form factor)?

Not so far as I know ... I'm thinking the smaller the better, especially on a bike, although one thing to consider is that the normal blade type fuses are still MUCH easier to find if you need one in a pinch and haven't brought along a few spares.

Regards,
Steve 8)