Voltage to helm gauges, what should it be?

AllanS

Active Member
Oct 30, 2020
180
Boat Info
1989 440 Aft Cabin
Engines
Twin Caterpiller 3208 (375 HP)
For you electricians familiar with the more classic Sea Ray cruisers, please help me out with a basic question: Should the voltage supplying the helm gauges be the same voltage as one measures at the house batteries when the ignition switch is on?

Here’s the context. My port and starboard voltmeters on the helm consistently ready low (11-12.5V), even when the engines are running, and I’m trying to sort out what might cause this. Today, as I was bulk charging my house batteries, and they were reading about 15-15.5V. I removed my helm cover and measured the +/- at each voltmeter, port was 12.58V and starboard was 13.11V. This match the display of the voltmeters, respectively, so the voltmeters are ok. Should there be a 2-3V voltage drop between the house batteries and the helm?
 
no they should essentially be the same at the meter and the battery.
Most overlooked is ground wires.
They need to be just as clean and tight as any positives it is a full circle in any electrical circuit.
 
There can be a difference from what you read at the batteries with a Volt meter and what you see at the helm. Could be accuracy of the meter, another factor is voltage drop. What size wire that is ran up to the helm and how far that distance is could affect it….

For you electricians familiar with the more classic Sea Ray cruisers, please help me out with a basic question: Should the voltage supplying the helm gauges be the same voltage as one measures at the house batteries when the ignition switch is on?

Here’s the context. My port and starboard voltmeters on the helm consistently ready low (11-12.5V), even when the engines are running, and I’m trying to sort out what might cause this. Today, as I was bulk charging my house batteries, and they were reading about 15-15.5V. I removed my helm cover and measured the +/- at each voltmeter, port was 12.58V and starboard was 13.11V. This match the display of the voltmeters, respectively, so the voltmeters are ok. Should there be a 2-3V voltage drop between the house batteries and the helm?
 
Thanks for the input. I used a Fluke multimeter on both batteries and helm readings, so I would agree that it is likely wire-size voltage drop or grounding. I’m leaning toward believing the latter.

Where are the grounding points that I should check?
 
Thanks for the input. I used a Fluke multimeter on both batteries and helm readings, so I would agree that it is likely wire-size voltage drop or grounding. I’m leaning toward believing the latter.

Where are the grounding points that I should check?

There will be a slight drop ~.2-.6v or so depending on how long the wire run is and the gauge wire used. But there should not be more then a volt at all The older boats usually have heavier wiring and are pretty good on the 12v side. As mentioned it sounds like a possible dirty ground some where, those are the toughest to find.

As long as your testing with the Fluke meter and not relying on the needle gauges you should be fine to t-shoot. Try measuring the voltage along the path of the wiring at every junction point including the 12v panel. Also keep in mind hat sometimes the connection will look fine but corrosion will be between the connection itself.
 
You may see a VERY slight drop in voltage between the two places - but as noted above, very small and relatively insignificant. The amount you're seeing is certainly not insignificant... also not surprising given that the electrical system is about 35 years old. And, of course, the biggest factor here is that it's an electrical system on a boat and it's subjected to harsh conditions.

Is everything else behind the dash seeing the same low voltage? Or is just the volt meters?

Run a temporary ground from one of the meters to a known good ground... or even a battery. See if that changes things. If it does - concentrate on the ground system. If it doesn't change things, look at the positive side.

In the end, you may very well have corrosion/broken wires (sometimes some of the wires break, but not all) on both sides.

Start with things in the bilge and behind the dash. Those areas are more likely to have the issue than somewhere in between.
 
Great advice, all. The voltage drop appears on all the gauges, but I have not tested the panel under the helm that feeds it. I do recall seeing different voltages every time I engage the ignition switches, so maybe that ground is corroded.

Which “cannonplug”?

I don’t have a wiring diagram of my boat, but found one for a 440 Express Cruiser that appears very similar.
 
Great advice, all. The voltage drop appears on all the gauges, but I have not tested the panel under the helm that feeds it. I do recall seeing different voltages every time I engage the ignition switches, so maybe that ground is corroded.

Which “cannonplug”?

I don’t have a wiring diagram of my boat, but found one for a 440 Express Cruiser that appears very similar.
Good find. Start there - especially if your switch feeds the gauges you tested (likely). It could be the wires/connections on the switch... or could be the switch itself. Check the supply wire to the switch vs feed wire to accessories.

Edit: This was already mentioned, but since it's both switches, a common ground is still high up on the list of culprits.
 
Great advice, all. The voltage drop appears on all the gauges, but I have not tested the panel under the helm that feeds it. I do recall seeing different voltages every time I engage the ignition switches, so maybe that ground is corroded.

Which “cannonplug”?

I don’t have a wiring diagram of my boat, but found one for a 440 Express Cruiser that appears very similar.

Your boat doesn't have a Mercruiser cannon plug. But you should have a terminal block either by the helm or in the engine room with breaker(s) on it.

Your gauges are fed directly from the engine wiring harness and I am not sure if there is a plug for that, but I don't think so, not in 89'.
 
On my boat the helm is powered by several switches. First, there are keyed switches separate for port and starboard on the main circuit panel, then breaker switches for each, also on the main circuit panel, then three-way switches (off/on/start) for port and starboard on the upper helm. So, lots of potential locations for corrosion and poor grounds. That’s where I’ll start. If that doesn’t help, I’ll start cleaning grounds and connections in the engine room.
 
Analog gauges and mechanical engines. For the Temp and pressure gauges the ground is the bias from the senders on the engines. Grounds to the gauges are required for lighting (obviously) and to operate the voltage, tachometers / hour meters. The gauge power comes from the key switches and engine ignition/start switches. Port powers port and starboard powers starboard. The question is are you getting the same voltage drop on both sides? And, where are you picking up the ground to measure the voltage?
It makes me wonder what has been added to the ignition circuit wiring over the years - quite possibly a voltage drop due to loads on that long 18 gauge wiring.....
 
On my boat the helm is powered by several switches. First, there are keyed switches separate for port and starboard on the main circuit panel, then breaker switches for each, also on the main circuit panel, then three-way switches (off/on/start) for port and starboard on the upper helm. So, lots of potential locations for corrosion and poor grounds. That’s where I’ll start. If that doesn’t help, I’ll start cleaning grounds and connections in the engine room.
Do you have a lower helm also?
 
No, just upper helm.
 
In a perfect world, voltage will be the same as it is at the battery. However, we know there will be a little voltage drop by time its reaches the helm. Any more then .5V would be a concern for me.
 
Just a follow up on progress with this issue, for those that may experience similar problems.

1. DC voltages between the house batteries and the salon DC panel are identical, so no loss there.
2. DC voltages at the keyed ignition switches and ignition breakers in the salon DC panel are same as house batteries.
3. Ergo, the voltage drop must be in the wire harness to the helm or at the helm itself.
4. Assuming the wire harness to be good, I cleaned all positive and negative terminals and bus bars under the helm, and verified that the voltage there was now equal to the house batteries. So far, so good.
5. Finally, I measured the voltages on the + and ground posts on the helm gauges (with the three-way helm ignition switches in the ON position). The voltages were higher than I had previously measured (port and starboard), but still 1-2 V lower than house batteries (15.5 vs 14.2 V). I ran a wire from a known good ground in the salon DC panel to the ground on the helm gauges, but saw no improvement in voltage.

So why the persistent voltage drop between the power bus under the helm and the gauges themselves? Is this because the gauges themselves are consuming power? Help me understand.
 
Just a follow up on progress with this issue, for those that may experience similar problems.

1. DC voltages between the house batteries and the salon DC panel are identical, so no loss there.
2. DC voltages at the keyed ignition switches and ignition breakers in the salon DC panel are same as house batteries.
3. Ergo, the voltage drop must be in the wire harness to the helm or at the helm itself.
4. Assuming the wire harness to be good, I cleaned all positive and negative terminals and bus bars under the helm, and verified that the voltage there was now equal to the house batteries. So far, so good.
5. Finally, I measured the voltages on the + and ground posts on the helm gauges (with the three-way helm ignition switches in the ON position). The voltages were higher than I had previously measured (port and starboard), but still 1-2 V lower than house batteries (15.5 vs 14.2 V). I ran a wire from a known good ground in the salon DC panel to the ground on the helm gauges, but saw no improvement in voltage.

So why the persistent voltage drop between the power bus under the helm and the gauges themselves? Is this because the gauges themselves are consuming power? Help me understand.
Brige across the Ign switches and see if it's the switches.
 
Just a follow up on progress with this issue, for those that may experience similar problems.

1. DC voltages between the house batteries and the salon DC panel are identical, so no loss there.
2. DC voltages at the keyed ignition switches and ignition breakers in the salon DC panel are same as house batteries.
3. Ergo, the voltage drop must be in the wire harness to the helm or at the helm itself.
4. Assuming the wire harness to be good, I cleaned all positive and negative terminals and bus bars under the helm, and verified that the voltage there was now equal to the house batteries. So far, so good.
5. Finally, I measured the voltages on the + and ground posts on the helm gauges (with the three-way helm ignition switches in the ON position). The voltages were higher than I had previously measured (port and starboard), but still 1-2 V lower than house batteries (15.5 vs 14.2 V). I ran a wire from a known good ground in the salon DC panel to the ground on the helm gauges, but saw no improvement in voltage.

So why the persistent voltage drop between the power bus under the helm and the gauges themselves? Is this because the gauges themselves are consuming power? Help me understand.
OK, so it seems you are narrowing down where the issue is.

-- You have the proper V at the bus bar
-- You DO NOT have proper V at the gauges

-- Follow each wire that leaves the bus bar and temporarily remove it from where it next attaches at. Measure V at the connector you just removed.
 
Right, I like your thinking (both of you), but I can't really access the 3-way ignition switches from under the helm. I might be able to get to the port switch, but just barely.
 
Now see if you have the same drop across the ground buss.

Check for any multiconductor plugs that join the main harness at some point. 1 loose or dirty pin can screw everything up.
 

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