Two Gauges / One Sender (Temperature and Oil Pressure)

[yvrmarc]

I have a 26' command bridge with helms in both the cabin and command bridge. I have the standard gauges at both stations but the temperature and oil pressure gauges both are connected to the one and only temperature/oil pressure senders on the engine. As a result the readings on my gauges are skewed. When I disconnect one of them at the sender the connected gauge reads correct. How are dual helm gauges suppose to connect to a single sender on the engine? Would I connect one gauge to the engine sender and connect the other gauge to this gauge? ... pairing one gauge of the other? Any feedback on this is greatly appreciated. Thanks

 

[UncleWillie]

No Title

You will need to add One SPST Switch near one Helm and a DPDT Switch near the other Helm.
Toggling either switch will transfer the Sender to the other Gage.

 

[yvrmarc]

Than you for your response, as well as the wiring diagram. Just so I understand your diagram ... the 2 dots represents the SPDT switch and the 6 dots represents the DPDT switch? Also I would need two of each as well correct? One set for my water temperature gauge and another set fot my oil pressure gauge? Or is there any way to have set of switches control both gauges?

 

[yvrmarc]

Thank you for your response, as well as the wiring diagram. Just so I understand your diagram ... the 2 dots represents the SPDT switch and the 6 dots represents the DPDT switch? Also I would need two of each as well correct? One set for my water temperature gauge and another set fot my oil pressure gauge? Or is there any way to have set of switches control both gauges?

 

[UncleWillie]

You could double up and use a DPDT and a 4PDT to switch both at the same time.
Adding a second set of Senders may be the simpler option also.

And Yes! 3 Dots = SPST. 6 Dots = DPDT.

 

[kjsAZ]

Dual helm setups require different senders with half the resistance of the senders used for single station! You can naturally use the switches and only use one instrument at a time but if you install the correct senders you won't have to run back and forth to switch on the correct place in case you forgot
See between first and second box in the attached PDF.
View attachment Sending-units-resistance-values_Faria.pdf

 

[UncleWillie]

Dual helm setups require different senders with half the resistance of the senders used for single station! You can naturally use the switches and only use one instrument at a time but if you install the correct senders you won't have to run back and forth to switch on the correct place in case you forgot

Bingo ! There is the real answer!
I wasn't aware that dual Helm Senders existed. But it makes complete sense in hindsight.

The question in the back of my mind all along is how the gauges ever worked from the manufacturer, and why do they not work now?
Did someone re-power the boat and install the wrong senders?

 

[kjsAZ]

I'd bet a used chewing gum against $100 that this was the case.... :watermelon:

On a more series note: Take an Ohm-meter and measure your sender. But as you already know that the instruments show the correct value with one only connected you know what senders you have.......

 

[yvrmarc]

Thanks for all your response. The boat is a 1974 and was repowered in 1990 with a Mercruiser 7.4 Bravo package. I have since had that engine completely rebuilt so I think that they wrong senders were installed, although they were taken off the old engine. I tried to find "dual application" senders for both water temperature and oil pressure but I have not been able to find any for my model. I do not have temperature and oil pressure alarms installed so I guess I can replace those senders with duplicates of what I have, but ideally I would have liked to install the alarms in the future.

I will keep researching the dual application senders to see if I can find one for my model year.

Thanks again for everyone's comments.

 

[UncleWillie]

The model year means nothing, just match the gage.
A search for "Dual Station Senders" gives a dozen hits.

The alarms are a separate Switch/Sender, and do not use the Gage Sender connections.
You add a Low Pressure switch, and a High Temperature switch for the Alarm function.