Topic: '74 CB750 Battery Leech

[MattRennick]

Hi all - long time reader, first time poster...

For the last week or so I've had trouble starting the bike and it looks like something is leeching power from the battery while the bike is off.  I've used a multimeter and a continuity tester to try to figure out what is drawing power and I think I've narrowed it down to one red wire that runs from the fuse to the key switch through the main harness.  I figured then that it was a faulty key switch but when I disconnect the switch power is still being drawn...

Has anyone had similar problems? Ideas of where to look? Rectifier? Alternator? Stator? Short of replacing the main wiring harness, or taking it to a shop, I'm kind of at a loss...

[Johnie]

Just some random thoughts...could the battery be bad and losing power when the bike sits? How old is the battery? Do you ever put it on a battery tender to keep it from sulfating? Is it acid or maintenance free?  Are the battery terminals nice and tight?

[nayto550]

First thing I would check is the battery itself.  Make sure the battery has a good charge, then take it to a shop or auto parts store and have it load tested.

If the battery is good, then it is time to start testing components (field coil, ignition coils, lights, etc...) for an amperage draw with the battery hooked up and ignition switch off.  Once you find what component is drawing amperage with the switch off, then you can track down where the voltage leak or offending component is.

[MattRennick]

Thanks a lot... Here's where I'm at.

Battery was fine (well, one of two was... I think I killed one) but I bought a third (brand new, maintenance free) alongside a new rectifier/regulator combo as I'd been able to surmise that a shot rectifier was to blame... At least I think... Anyway... So I installed the reg/rec combo today and the regulator side of things seems to be working well but the rectifier?

Well... If I try to build the block coupler one way I blow the main fuse and if I build it the other (just swapping position of wires) I effectively hot-wire the bike and it's on even without a key in the ignition... I'm kind of at a loss and am likely going to have to bring it in to a mechanic in the next couple of days.  Unless any of you have any ideas?

[nayto550]

Well... If I try to build the block coupler one way I blow the main fuse and if I build it the other (just swapping position of wires) I effectively hot-wire the bike and it's on even without a key in the ignition... I'm kind of at a loss and am likely going to have to bring it in to a mechanic in the next couple of days.  Unless any of you have any ideas?

More detail is required...  which wires did you switch (colors), and exactly which coupler are you putting together?  Any other specifics would be helpful as well.