2003 Honda BF50a fuse blowing

Honda BF50a, second season with it. Ran fine last season, had a mechanic go through it before this season (got it late last year). First time out this year, and it's blowing the 10a fuse by the starter. Remote trim and ignition are not working after the fuse is blown. Trim on the motor itself is working. I can start the motor immediately after I insert a new fuse, but it burns out after about 20 seconds. I'm getting 14.5 amps on the multimeter at the site of the fuse. I know I could probably just toss in a 15a fuse and call it a day, but the fuse holder is clearly marked 10a. Any suggestions other running a wiring harness? My electric experience is novice at best.

Don't up the fuse rating!!! You were WISE not to go there!
All that'll do for you is catch some wiring on fire!

You already know there's a high amp condition in the CIRCUIT (or one of the circuits) that the fuse....and here's the important part....FEEDS voltage to.

A high current (amp) draw can be caused by either a defective component or a short to ground in the circuit wiring.

You will need a wiring diagram and probably at least a rudimentary "tester" to find this problem.

The first step is to use the diagram to identify which components this fuse FEEDS voltage to and unplug or unwire them.

With all fed components unhooked, does the fuse still blow when power is applied to the circuit? If the fuse blows then a wire has probably rubbed through and is shorted to ground someplace. Many times a careful visual inspection is all it takes to find that spot. Look where the wires are tightly bent around corners or where they are subject to a lot of movement and chafing. Sometimes the insulation will wear where they go through a holder or clip meant to hold them in place. Also look for pinch points where a wire or harness could get caught or crushed by something like a lever or mechanism. Inspect all terminals and plugs for deterioration or damage. Sometimes a single strand of wire can "sprout" out of a terminal and create a short. This can even happen inside a plug socket sometimes.

If the fuse doesn't blow with the components disconnected, then plug each component back into the circuit one at a time and see which one causes the fuse to blow.

I made my own tester by soldering a fuse holder to some wire that I could hook to the battery positive terminal with a larger spring clamp. On the the other side of the holder another section of wire with a small alligator clip makes it easy to hook onto a fuse clip. I use several different kinds of ends on my tester for hooking to blade sockets and terminals. It just comes down to what works best.

I install a lower amp fuse into the holder and apply power to the wire that the permanent fuse would feed. This will show you when a short is present and will protect the wiring at the same time.

Simply remove the regular fuse from its spot and check which terminal in the holder gets voltage. Leave the fuse out of the circuit and use your test wire to apply battery voltage to the unpowered terminal of the fuse holder. You are simply substituting your tester as the voltage source for that circuit.

If you plug in a component and the fuse blows, it is likely that the component is shorted or drawing too much current.

Question:
Are you sure that you're measuring amps and not volts? When running, the charging voltage would be right around 14.5 volts.

How are you testing amperage with your multimeter? Are you using an inductive amp clamp plugged into the meter?

I ask because most multimeters alone only test for 10amps and require that you put the meter in series with the circuit. Which, by the way, I don't recommend doing as it usually destroys the meter in high amp draw situations.

There are other ways of going about finding high amp draw including thermal imaging to locate hot spots as well as some pretty sophisticated and expensive electrical testers. But even a lot of the pro shops can't afford all of that stuff.

Hopefully others here have some good tips to help you find your gremlins.

Good luck.

That fuse should be powering everything. It's the only fuse on the motor. It powers relays used for the trim/tilt and starter motor.

What is weird is that the remote trim stops working but the trim switch on the motor continues. Those 2 switches are wired in parallel. Neither are very likely to be causing your issue.

As much of a DIY advocate as I am, I think that maybe this issue may be out of DIY territory. A rookie trying to figure out ANYTHING using the Honda wiring diagram doesn't have much of a chance here.

So, I had the mechanic at my marina look at it, (took several weeks as they were backed up) and he figured out it has something to do with the tach- when he disconnects it, no more blown fuses. When it's plugged in, starts blowing them again. Last time I was out, before he found the problem, I left the fuse in for the hell of it (I was starting it and removing the fuse) and it functioned like normal for about 20 minutes before the fuse blew (tach and power trim stopped working). Should I just start with replacing the tach? I found another thread where honda dude mentioned a resistor that was used on older 50s. Gonna see if I can find that on and look for corrosion/wear. I will also check the harness once I pull it out this fall. For now, I don't see much harm in running without the tach. I almost never run WOT and only for short periods.

My guess would be it's not the tach itself, but more likely the wiring leading to it. Agreed, running without won't hurt a thing. Will give you some time to "get around to it".

Congrats to your mechanic for isolating that issue. Those are nearly always toughies......

In searching for blowing fuses on my old 12 volt cars, instead of a fuse, I wire a taillight bulb in place of the fuse. I use a bulb and socket for the brake/signal lights, I think it’s the 1157. I place this via long wires where I can see it and keep disconnecting or connecting things, playing with wiring, until I find the problem. The 1157 is strong enough not to blow the bulb from a short amd I don’t have to keep replacing fuses plus trying to see a fuse box while checking out the problem. This should work here as well?

Any (test) light can work. If there is a path to ground the light lights. If there is an open circuit (as it should be if everything is turned off) the light won't light.

I used to do the same on 12v systems in about anything. Set the light up between the battery and either positive or negative cable after removing it. Then start pulling fuses until the light goes out. When the fuse is pulled that lets the light go out, you've found your problem circuit. Then, you can move your light leads to either side of the fuse. The light lights indicating there's a path to ground on that circuit. Trace the wiring on that circuit to find your issue. Honestly though, depending on what you're working on, sometimes it's much faster to just run new wire..... from lessons learned while working on motor homes and travel trailers for 20 years......

On the 40-50hp Hondas, that fuse supplies everything from power to the tach and trim guage, the tilt system, the starter relay, a bunch of stuff, which leads to a LOT of possibilities. To isolate a bit (if we didn't know it was the tach lead), you can pull the black plastic cover off of the junction box, and separate the wires in there one at a time to find your issue/problem circuit.

Alan Hicks said:

Any (test) light can work. If there is a path to ground the light lights. If there is an open circuit (as it should be if everything is turned off) the light won't light.

I used to do the same on 12v systems in about anything. Set the light up between the battery and either positive or negative cable after removing it. Then start pulling fuses until the light goes out. When the fuse is pulled that lets the light go out, you've found your problem circuit. Then, you can move your light leads to either side of the fuse. The light lights indicating there's a path to ground on that circuit. Trace the wiring on that circuit to find your issue. Honestly though, depending on what you're working on, sometimes it's much faster to just run new wire..... from lessons learned while working on motor homes and travel trailers for 20 years......

On the 40-50hp Hondas, that fuse supplies everything from power to the tach and trim guage, the tilt system, the starter relay, a bunch of stuff, which leads to a LOT of possibilities. To isolate a bit (if we didn't know it was the tach lead), you can pull the black plastic cover off of the junction box, and separate the wires in there one at a time to find your issue/problem circuit.

Click to expand...

Thank you, the mechanic soundly highly irritated it took him so long to narrow it down. There was a lot to go through there. I'm going to inspect the wiring and try and narrow it down, if I can't find anything wrong, I'll start replacing the cheapest parts first. (Resistor, harness, guage)

Prior to replacing expensive gauges, try disconnecting the wiring right on the back of them. If the short goes away, you have your culprit (the gauge). If the short is still there with the wiring on the back of the gauge disconnected, safe bet there's nothing wrong with the gauge.