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225 alternator light on constantly

M

metal-chicken

Regular Contributor
Not been to the boat for a couple of weeks but I did know that my engine battery (of unknown age - certainly > 5 years old) had died a few weeks ago but I switched the Blue Seas (ACR) switch to emergency and the house battery fired it straight up.

I ran (mostly idling) with the odd blast between fishing spots for an hour and only realised after about 30 mins that the alternator light was on solid but the voltage gauge showed 12.5-13v.
About 4 weeks ago I put a voltmeter on the bettery switch terminals while the engine was running and it showed 13.5v while the gauge showed 12.5v.

So does this mean that my alternator is dead or does the alternator light get a reading from the engine battery? Or something else?

Would a pretty well charged house battery run the engine for that long (it ran fine)?

Obviously a new battery will be fitted when the boat comes out of the water in a couple of weeks time.
 
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The voltmeter on the Honda digital gauges is run from the ECU. On my boat, the voltage from the ECU reads 13.4 volts. I have a separate voltmeter hooked directly to the battery and it reads 14.4 volts when engine is running.

Simple test of alternator output - with engine off, measure voltage at battery terminal. It should be right at 12 volts, +/- a little bit. Then start engine and measure again. It should be around 13.4 to 14.4 volts or so. If so, your alternator is charging battery correctly. Given that, check the wiring to the digital gauge. It's a 4-prong connector. The alternator wire is white with a blue stripe.
 
No digital gauge.... just an analogue one. Forgot to say, no alarm either.... just the light.

Back to the boat early next week to pull for the winter so I'll take my voltmeter and run a few tests.

When I replaced the house battery last year (I installed the ACR at the same time) I fitted a 115Ah leisure battery - can I do the same again for the engine battery or should I be looking at something else?
 
You should be installing what is usually called a "cranking" battery here in the US. You want a battery that will deliver at least 800 cold cranking amps (CCA) according to the owners manual.
 
Just thought I'd follow this up..... although I haven't got a new engine battery yet I started and ran the engine using the house battery this morning and the alternator light was still lit. The analogue volt gauge was showing 13v when the engine was running but when I put my multimeter on the battery terminals it was showing a solid 14.6v - so I'm pretty sure the alternator is fine and that something else is going on with the alternator light.

I'm also wondering why the voltage gauge on the dash is so far out... maybe the needle can't go higher than 13?
 
I suspect you may have a corroded connector somewhere in that maze. Check your harness from engine to instruments and all connectors that have a white/blue wire, which is the alternator sensor wire.
 
it could be that instead of you getting half wave rectification you could be getting full wave rectification although it shows that its charging you possibly have a faulty diode thats why the light stays on.
 
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