Electrical system low voltage issues

[captainmaniac]

Here's one for the engine / instrumentation wiring experts out there... This is going to be a bit long to get all the pertinent details in.

I have noticed for a while that my voltmeters don't read as high as I thought they should. Under way at a good RPM (3000 roughly) they would read between 12 and 13 volts, while I expected about 13.5. I thought (hoped) it was just some gauge calibration issue but recently tested it and found the gauges to be accurate - my digital volt meter matches the voltage shown on the gauge. What is worse - at lower idle RPMs (< 1000) my Port usually reads between 10V and 11.5V. I have put the voltmeter across the battery and the gauge and verified that the battery has (mostly) full charge, but the instrumentation is not getting 12V. From that, I have been suspecting alternator or voltage regulator.

Then something new a couple of weeks back. While idling (800 rpm) for a while my port voltage dropped off the gauge... Over the span of about 20 minutes the reading fell from 10.5v, down past 10, past 9, and then fell off the bottom of the gauge. When I throttled up to 3000 rpm the voltage came back up to 12ish, but it almost looks like the charging system gradually shut down while idling for a long time. Again, the gauge reading is accurate - my instrumentation (and presumably engine electrical system) was running on way under 12v... Not good.

Now it gets interesting....

I was looking through the wiring diagrams and other info in the manual, I found a note that by turning ignition on (but not actually starting the engines) the voltmeters are supposed to show me the state of my batteries. BUT when I try it (ignition to On position only) I get only 11.1v at the instrument panel while the battery itself measures 12.2v. On the starboard side, I get 12.6v at the battery but only 11.8 at the instrument panel. I am losing 1.1v in the port side and 0.8v on the starboard. Since nothing is running this has nothing to do with the alternator or voltage regulator (I think the reg only gets involved when things are running).

Looking at the wiring diagrams, the panel voltage is not coming directly from the battery - it is from the ignition system / engine wiring. Power is going from the battery, through the starter solenoid, through the ballast resistor, I can't tell if the ECU or ignition coil play a role at all since they both wire to the ballast resistor as well, and I don't know what all else, before it makes it to the instrument panel. Somehow I am losing voltage over bad wiring, bad ground, or devices along that route.

Has anyone else seen / experienced this, and if so were you able to resolve it? I still have some diagnostics to do to try to figure out where the voltage drop(s) are occurring, but any insights from you guys would be appreciated. I don't know if I just have one problem (affecting voltage whether running or not) or multiple (one affecting voltage all the time, plus possible voltage regulator or alternator output issues while running).

[sehord]

Electrical issues are a pain and can really be tough on your electronics. Check the voltage at the battery then check it at every point avaailable alll the way up to the panel. I just changed an old fuse panel that looked great, no corosion, but I had 12.6 in and about 7 coming out. ery wierd, but it was faulty. If you cannot find a difference at one particular spot, then Have someoone hold a meter on your gauge wiring and then have you wiggle all visible wiring from your batteries on up to look for any spikes from a poor or coroded connection. Pay very close attention to your main ground, and you may even make a temporary jumper from your ground to the volt meter and then to the positive on the gauge to verify. It could truly be anywhere, but since you have it on both engines I would look at all common grounds.

[Big D]

Sehord is right; electrical gremlins are perhaps the most challenging and time consuming faults to resolve. Do a voltage drop check as he describes (check voltage at each terminal along a circuit. When you get a difference, the fault lies between the last check and the one you checked just before. The "Wiggle" test (actual manufacturer diagnostic term!) is also great for finding bad connections. Turn ign switch to ON and start willing everywhere to see if the gauge changes. I suspect you have Chryslers? Check the engine harness connector by separating the two halves and inspecting for corrosion or a contact pulling away from the connector. Don't forget to wiggle it as well.

I also understand that some models had auto switching relays behind the helm that fail sometimes, and I don't exactly know much about "the box" behind the batteries, but anything in the system that may be common to both engines/wiring systems is suspect. The ground is a good place to start.

[randyp]

I've fried a couple of alternators when I was starting out (was a former sailboater so dumb as a rock when it came to all things inboard). At first your symptoms sounded like that. But if you are getting some voltage rise when you increase throttle the alternator(s) is/are functioning......but maybe not to spec. Check your belts and do a voltage check on the alternators. Voltage regulators could also be a problem here. Check for loose connections off the batteries, off the battery switches, etc. Finally the battery switches themselves. This is the gremlin that ate my first 2 alternators! Bad post on "1" meant that the switch was basically "off" while the alternator was on while engine running - a sure killer if you don't have an overide switch.

[aweimer]

I would be looking for a grounding issue. Being that your gauges dropped to zero and you know that isn't possible with 11-12 in your batteries i would be tracking a grounding problem.

Not fun stuff. I had the same thing this season as well. Take your time and look for corrosion/loose connections.

[captainmaniac]

Finally managed to get some time today to look a bit further. It's hard to measure voltage at each connection along the circuit as its hard to figure out where the circuit really goes!

One thing I did notice was with ignition ON (not running, but switch in the ON position) I have 12V at the battery and only 11V hitting the gauge cluster... BUT if I disconnect the wiring harness from the 'control unit' for my electronic ignition or unbolt the ECU so it is no longer connected to ground, my cluster gets a full 12V. Don't know if I am just altering current path by farting around with the ECU, or if this is a sign the ECU has a short in it or something. Any of you electrical gurus out there have any relevant thoughts ?

[randyp]

Another opinion on this one. I only have a single engine, but my volt gauge reads under 12V when idling along after starting the engine. I always have the blower on when I'm starting out and at low rpm (under 1200). What I've found is that when I "goose" the throttle after turning off the blower the gauge will read above 12V, and after a while up in the 13.5 range. I've confirmed with with my GPS which has a voltage read out. The voltage regulator on my engine (Chrysler 318 electronic ignition) kicks out higher voltages after the alternator starts to crank the volts at higher rpms. I've found that I have to be over 2000 rpms to get this to happen. If I'm just cruising around at under 2K rpms, I'll put it in neutral and goose the throttle a couple of times, watching the gauge. I think you may be having the same issue. I discovered this on our canal trip when all of our speed was under 10mph (under 2K). Just my opinion, hope it helps.

[prowlersfish]

Most likely losing it on the ground side .BTW the power to the ignition switch does not go thru the ballast resistor