Looking for switched power on my BF90's

John S

I was hoping someone could give me some advice. I have a fuel flow meter on board my Tomcat. I wired it into the accessory switch because it was easiest. I would prefer to tie it into an ignition swithced power source from both motors, I would also need to wire it where electricity couldn't flow from one ignition source to the other thru these wires.

Anyone have any advice on where to get started?? I have twin Honda BF90's.

Les Lampman · Posted: Mon Apr 30, 2007 12:52 pm Post subject:

John,

I'm assuming the fuel flow meter is at the dash and the ignition switches not too far distant. I'm also assuming the stock Honda wiring harnesses were used. If so...

The black/yellow wire on each instrment harness (the one from the keyswitch panel to the instruments) is "hot" when the key is on. You should be able to find an unused connector behind the dash; make sure you find one for each engine (and each does have a separate harness). So there's your ignition controlled power.

Now, for the either/or situation. Wihtout getting into diodes, latching relyas and the like the simplest is to just let it get power from one or the other and not worry about both. But you didn't ask that so the next easiest is probably with a small toggle switch (and we're talking really low amperage here). Get a single pole double throw "on-off-on" switch and install it somewhere; run the port side lead from the black/yellow connector you found to one side of the switch, run another lead from the starboard black/yellow connector to the other side of the switch, then run a lead from the center of the switch to the fuel management gauge. Get the switch oriented horizontally and the wires on the ends connected so that flipping the switch orients properly with port and starboard and you should be good to go.

Have fun!

John S · Posted: Tue May 01, 2007 4:16 am Post subject:

Les,

Thank you, your response is very helpful, I'm sure I have the original Honda wiring harness. I will look for the yellow/black wire.

We do troll and cruise single engine at times. Is there any reason I wouldn't just want a diode in line on each power input. Is it more complicated than just going to a radio shack and asking for a diode? In other words are there lots of different rated/types of diodes.

I know the switch would work, but if I can make it automated that would be preferred.

If using a diode, would it be appropriate to splice it into a length of wire and just use a length of shrink wrap tubing in that area to protect it?

Thanks for your help.

Almas Only · Posted: Tue May 01, 2007 5:46 am Post subject:

Search "wiper blade parking" for specifics regarding size and installation of the diode which allows the wiper blades to "park" properly. Then check your meter, and see if it draws more than 5 amps current. If not, use the same Radio Shack PN as furnished for the wipers. If your wipers don't self park, put one in that circuit too, as they come in a 5 pack, as I recall.

Good luck!

david on Alma's Only

John S · Posted: Tue May 01, 2007 1:53 pm Post subject:

Thanks for the lead, I read the whole thread. My fuel flow meter is a Navman F3100 it only draws 75mA. Do you still think the Diode with a capacity of 5 Amp would be best?

I noticed there were LOTS of different diodes available at Radio Shack.

Thanks again,

Almas Only · Posted: Tue May 01, 2007 5:23 pm Post subject:

John:

See what Radio Shack says on sizing -their web site was uninformative - but I guess my approach would be to check the fuse spec. for the unit drawing the current, and size the diode slightly higher (say, for lack of anything more precise, 1.5 -2x). That way you would avoid having an undersized diode serving the role of a fuse, and still not have the diode so oversized that it is dropping your voltage to the unit.

Remember, diodes don't like getting cooked with soldering irons.

Let me know how it turns out.

david

John S · Posted: Tue May 01, 2007 6:50 pm Post subject:

Thanks for the advice, I'll definitely crimp and post what I find out once this is done. I'm a couple thousand miles away from boat right now, so it won't be right away.

Thanks again,
John

John S · Posted: Sun Jun 08, 2008 3:06 pm Post subject:

I finally installed the Diodes this spring and now the fuel flow meter works of the Honda key switch. All went well and the advice on which wire to use was correct. Only one strange thing, the fuel flow meter has a voltage meter built into it and one of the diodes causes a voltage about 1 to 1.5 volts different than the other. Maybe I got one too hot with the heat gun.