Low Voltage

I have an 89 SN with the original alternator. The other night at the lake, I noticed that when I turned on my nav lights the voltage meter dropped below 12 volts. If I turned on the blower too, the voltage would drop to around 8 volts. With just the engine running, it normally runs around 13 volts. Is this a sign that my alterator is starting to die, or could I simply have a bad connection somewhere? Any suggestions on how to diagnose the problem?

Thanks,
Mark

I had the exact same problem in my '89, as did the mechanic at my Nautique dealer. When I turned on the lights and blower, the volt meter would drop, and the temperature gage would bump up 10-15 degrees. When I hit my spot light, the low voltage alarm started singing.

In my boat, the problem was in the grounding of the gages. All the dash gages had their grounds connected in series, then back to the ground block. There was enough resistance in the connections from gage to gage that I measured 1.5 volts from the ground block to the last gage. My solution was to connect each individual gage grounds directly to the ground block. I also ran an additional heavy gage wire from the battery (-) to the ground block. After doing this, the gages remain normal when accessories are turned on.

Hope this helps.

Thanks for the input guys. I will take an external meter and and try and determine if its a gauge problem or if the voltage really is low.

64 Skier, when I crank the engine, the volt meter has always dropped low. Is this normal? It doesn't seem to be cranking slow and I don't have any trouble starting. With the key on and the engine not running, I get a reading of about 11 volts.

Jeff, when you had the grounding problem with your gauges, did it also effect the gas gauge? I have had my boat for 3 years and the gas gauge has always had problems.

Kenny G, my alternator has the external regulator. Would the diodes you mentioned be part of the external regulator or are they still internal to the alternator? If the problem does turn out to be the alternator or regulator should I consider upgrading to a new alternator with the internal regulator? The upgrade is kind of pricey.

Thanks,
Mark

You should have 12 volts, and it sounds like your gauges reduce the voltage as much as the starter does. Did you read the 11 volts with a Volt meter or your gauges?

I think Jeff is correct and your first efforts should be the ground wiring of the gauges. Then start up and test the alternator output.