2001 bf 90 battery drain

2001 bf 90 with brand new battery, load tested good and engine charging 12.6 v and isolated from other 12v accesories. In 2-3 days sitting on the lift the battery is slow drained down below starting ability. I dont see a rectifier on the parts list- i was thinking a faulty diode discharge. Not sure how to check it. Any suggestions super appreciated. Thanks

The engine pulling the battery down would be a new one on me. Not sure how you are "isolating", so let me ask you. How hard would it be to disconnect ALL on board accessories, especially the radio and anchor/nav lights, physically (like pulling all of the fuses) to see if you still have a drain?

Alan, thanks for the reply. The fuse box that powers all the accesaories like vhf, pumps, nav lights etc is disconnected from the battery thus isolating the outboard from any potential parasitic 12v draw. With ONLY the battery cables from the outboard connected there is still a voltage drain that discharges the new battery in 2 days. A bad diode in the rectifier can cause this but the parts diagram doesnt show a rectifier. So where is the drain coming from and how do I identify it? Thanks

Under the motor's hood, there's a couple of fuses covered with little snap on covers in the area just forward from the starter - left front corner let's say. I forget the particulars as I haven't had to do what you need to do recently. I would pull those fuses. They power ALL of the individual circuits. More detail available studying the wiring diagram in the back of the owner's manual. Those are available from a lot of sources on line for free. Rectifier/diode location escapes my memory, but if the motor is charging properly, I doubt you'll find anything wrong there.... -Al

Your post is a bit confusing to me. You say that the system is charging but it's hard to discern if it's charging at 12.6 volts or if it's maintaining the battery at 12.6 volts. There's a big difference between the two meanings.

Quote: "engine charging 12.6 volts"

Your outboard has an alternator and therefore will have a voltage regulator. That's why you don't see a rectifier assembly. The rectification is done in the alternator via diodes.

You are correct to suspect a shorted diode as that is often the cause for a key off drain.

If the alternator is charging near 14 volts and the battery at rest volts are 12.6 then it's not likely the diodes in the alternator causing the drain.

BUT...
...I would still unplug the alternator to see if the drain goes away as an internal wiring fault could still cause a parasitic drain on the battery. Unplugging the voltage regulator is also something you might try as doing either one is fairly easy and doesn't require any test equipment.

Finding a drain usually turns into a process of elimination and those are a couple of good places to start looking.

Good luck.

I have 2 of these 90's for my personal use (love them both!), and neither have an "alternator" w/internal diodes like you might see on a car for instance.

See parts diagram for layout of the system used-
https://www.boats.net/catalog/honda...a-vin-bbbl-3000001-to-bbbl-3099999/alternator

See #1 for rectifier
https://www.boats.net/catalog/honda/outboard-by-year/1998/bf90aw-lrta-vin-bbbl-3000001-to-bbbl-3099999/regulator-starter-cable

Not denying the potential for a shorted diode to be sucking power. My comment was regarding that if I run into one, it would be my first.

My mistake!

I guess "rectifier" is an amperage limiter in this case. Much like a lawn tractor charging system I suppose.

I should have seen that one coming!

In either case, unplugging those devices might still be something to try to see if the draw goes away.

Sorry for any confusion I may have caused!!

A "rectifier" is a twin to a diode bridge. Works the same (3 wires in, one wire out), just looks different because it's potted.