Voltage Issue
 

Last night running with the nav. lights on (~3300 RPM), both voltage gages read ~12 volts and would drop to ~10 volts or lower when ever I would use the trim switch or tabs. I also noticed that the higher the RPM the lower the voltage on both gages would drop. At idle both would rise to ~ 13 volts. Ran for 60 miles and no change in readings.

I did remove and clean batt. connections on both batteries in the spring, however both were clean.

Engines:1992 T- 502 mags

Planning to go to the marina on Monday to try to diagnose the issue. Any suggestions???

I have the same problem. I believe I either have a voltage regulator or isolator problem. At idle, voltage reads OK, it slowly drops to 10v at 1800 rpm and starts to rise again with more rpm.

Be sure to use an accurate voltmeter, digital if you have one.

A voltmeter doesn't tell you SQUAT... Amps charge a battery, voltage is the by-product of the amps. You need an amp clamp and multimeter, of better yet, a charging system analyzer that checks for AC volts, which is what happens if a diode fails. Guessing costs lots of money... spend the money on a proper, accurate diagnosis with the proper equipment to do so.... it will save time, and a bunch of money (unless you like changing things for no apparent reason) with no results....

gauges
 

Don't panic just yet. This problem normall happens when you have a loose ground and the switches pull ground from your gauges. Remove the dash panel with the gauges in it and be certain that the brackets that hold the gauges in place are tight. These bracket supply ground in the circuit. With 2 aligator clips and some 12 gauge wire run one end from the gauge bracket and the other end to the - battery terminal. Now throw the switch. If everything is OK reinforce the ground, if there still is a problem- check for loose connections.

Thanks for the info, I'm headding to the boat now. Will post what I find, hopefully I'll find something.

What is the tell-tell sign of a battery going south?
The batterys I have in there are ~4-5 years old. It has allways started fine though.

The batteries could show 12 volts but the amperage could be way down. Remember the amps are what does the work. You probably have a grounding problem also. 4-5 years out of a battery is good.

Update
 

Ok... spent some time this PM trying to find the issue, here is what I found.
1. Both batteries were at 12.7 V, so running for 60 miles with the gage reading 12V or less was not what the Batts were seeing.
2. Found the ground block at the dash panel to have somewhat loose connection screws, tightened ~ 1/4 turn on each.
3. Disconnected all in-line molded connectors and all looked like new.
4. With engines off and all interior loads from the dash panel switches on, the voltage gages were reading ~ 1.6 V less than the driving batt. Ground had only 0.1 V drop, the power had 1.5 v drop. Now, where is this drop coming from, or is the path quite long with the engine off?

One issue, I do not have a clear understanding of the path for the 16 ga. purple power feed to the volt gages. Anyone have a schematic showing this path? If so, an E-mail would be appreciated, [email protected], thanks!

Any other suggestions?

VD Voltage drop
 

OK the ground side looks good and the power side is losing 1.5 volts.
I have a question
1. are you using an isolater? Since isloaters are just heavy duty diodes a .6v drop would be normal. that would mean you are loosing 1 volt. This can happen if the wire that supplies voltage to the gauges is coroded and as it heats up the resistance goes up which would show a lower voltage. The simple fix would be to replace the wire with the same size that is in their now then recheck the voltage at the gauges.
Battery going south...You can look for obvious sign low levels of fluid, discharge through the case...Take you volt meter and touch one end to positive terminal, the other end to the plastic case about 1 inch from the terminal. Do you show voltage? Clean the top of the battery with baking soda and flush with water. The real test of a battery is a load test which can be performed at most auto parts stores. This test checks the reserve current capacity of the battery...if its bad or weak replace it.

Baja 2700, no Isolator installed... just the bat. switch for controls. I will pull the batteries this winter and have them load tested, I did look at my records and they are 5 years old. It is probably time to replace them with a fresh set.

As for the wiring, all connections look good. The only thing in question now are the squeeze crimps at the circuit ends. Will bring my insulation piercing probe and trace the voltage drop.

To my understanding, the voltage guage feed runs to the engine connector (pin 5), then it runs to the alt. All circuits remain purple in color. Is this correct? I still do not understand the alt. wiring. According to my schematics, there are 4 wires coming from the alt. Main ground and generating output (orange) are clear to me, what are the other feed paths (purple-feeding the guage? and red/purple) assuming they are regulator feeds, what are their functions???