AMPS warning light stays on?

[jtryon]

So I've had my '88 Sunsport out three times so far this Spring without any issues, aside from the "AMPS" warning light on the dash staying on. It starts right up every time and is showing ~13 volts charging on the dash. Before going out this past Sunday, I checked both batteries (deep cycle) which are running off a Perko switch, and both showed 12.70 volts, so they are definitely being charged. Ran the boat for 8 hours Sunday and the light was on the whole time, but experienced no issues. Played music the whole time, anchored for a bit with just music on, and she started right back up. Could the light just be stuck on? What's the best way to check amperage on the batteries to see if I might need to replace one or both?

[CJD]

The light is a function of the alternator, not the batteries. It may be sensing a bad diode, which will still charge but at a lower amperage.

[jtryon]

that makes sense. that alternator was new last year from skidim too, damn.

[wotan2525]

Actually, I believe that all of the warning lights are controlled by a little circuit board that is below the dash. This also has a buzzer that will turn on to warn you of problems (and has almost certainly been disabled after driving a previous owner mad.)

I believe that parts of these boards fail all of the time. My alternator is strong and keeps everything charged and working great -- I still get an AMPS light from time to time. I also get an oil light that comes and goes -- even though my gauge indicates that I've got great oil pressure.

My money is on that board causing problems -- I'd ignore it if I were you. If everything works and stays charged, who really cares about a blinking light?

[CJD]

Well...me. When an alternator does go out, you're not getting back to the dock. If you have a bad light and ignore it, it will bite you sooner or later.

[leetudor]

12.7 volts with engine off or running?

[jtryon]

12.7 volts with the engine off. that was taken after my first two trips out with the boat and probably a good 5 hours of running time.

[leetudor]

you need to check it with the engine running to see what type of voltage that you have..

[jtryon]

the dash gauge says 12.5-13 volts when it's running depending on what accessories are on. i'll test tonight with my multimeter while on the water.

[CJD]

The dash voltmeter is notoriously inaccurate. For diagnostics you will need to read it with a decent multimeter to be sure.

[jtryon]

I checked it with a multimeter last weekend and am getting 14.4 volts at the battery while the engine is running. Seems to me everything is fine? This is 5x out this Spring with no power issues other than the light.

[UKandH]

Hi.

Here is my take on the system (i am an automotive electrical design engineer)

I had similar issues with the temp warning on my 94 Comp and this is what i found.

There is an ECU under the instrument area that has various input / outputs. The unit is designed as a differential comparitor, it will measure the inputs vs known values, if the voltage in the battery pack falls below 10V the WL will come on. The usual way of having a warning light wired up is via the diode pack on the alternator feeding 12V to a bulb on the dash, then the alternator is not rotating the 12V is grounded via the diode pack, one side of the bulb has ignition feed and this then passes to ground when the alternator is at rest putting the light on. When the alternator is running the diodes then feed that wire with 12V which then puts the bulb out (12V+ one side via ign switch and 12V+ from the diode pack = 0V hence bulb goes out)
The supra control module does not work this way, it expects to see a voltage above 11V only, as the battery drains because of no charge from alternator, the light will come on in time to get you back to the trailer or shore. Its not a great system to be honest. Things to check would be
1/ Check the ign source to the unit is at battery voltage.
2/ Engine running and voltage increases to 13.5V minimum.
3/ Check amperage output of alternator by using an ammeter whilst running.

If all is ok then your ECU is kaput. I suspect a dodgy board, if you can get it apart look at the soldering on the board for corrosion and bad connections. Check resistors for the same.

My personal opinion of this unit is it is of poor quality / reliability. But you have to think how old they are now!! so considering that, its not that poor really and i guess Supra really didnt expect to see these boats still being loved as much as we obviously do.

I would rewire the system to a traditional layout (as described above)
Water temp to a traditional gauge system, ignore the warning lamp
Fuel the same, fit a transducer that has low fuel warning switch built in if you need a warning lamp
Oil with gauge and low pressure warning lamp (there are 2 switches on the engine one for gauge the other for warning lamp)

Regards

Andy