Can't get gauges to work...

[Holy Shamolee]

I have a 1980 25S Tollycraft. Someone replaced the motor and never got the gauges to work afterward.
I just put a new 5.7 Mercruiser engine in it.
It was wired for a Volvo.
I can not get anything but the tach to work.
When I got the boat, all the gauges were pegged right.
I put a new SW oil gauge in it,
It sort of worked. It went up to 50 when I started the engine but soon pegged left and then shot up to 50 again. Pegged left and quit working.
Even the volt meter will not work.
Light blue for the oil sender.
Grey for the tach.
I'm not sure about the water temp as on the mercruiser it is blue and goes into the electronic ignition module.
I have been at it for weeks and am losing my mind!!!!
Help Please.

 

[glenn property of pam]

Re: Can't get gauges to work...

sounds like a ground problem if you have a volt meter put one probe on any black wire of the gauges and then put the other probe on the battery dc- post if it reads any voltage then you have a bad ground between the 2 points. check for bad connections (rusty etc) on all the black wires. start simple and just try to get the volt meter on the dash to work first as thats a simple one and the chances are that when you find why that one is not working you will find the real problem

 

[Holy Shamolee]

Re: Can't get gauges to work...

The volt meter has 3 terminals.
GND
I-Ignition which I believe is 12V from the Ignition switch.
S - Sender.
It reads about 10 volts with nothing hooked to the S terminal.
If I hook 12v to the S then it pegs left.
I don't see a sending unit for the volt meter.
I would imagine it would be a power wire from the battery.
or even the ignition switch

 

[Silvertip]

Re: Can't get gauges to work...

There is a sticky at the very top of this forum (not this page) titled "Generic Boat Wiring Diagram). Study it and you will see that the only ENGINE related gauges are those that require senders. the tach sense comes from the ignition coil, the fuel gauge sender is in the fuel tank, the temp sender is on the engine as is the oil pressure. +12 volts for all gauges comes from the "I" terminal on the ignition switch. Ground is wherever you find it at the helm. Those two wires are simply daisy chained from one gauge to the next. If the tach works then follow the +12 volt and ground wires to each of the other gauges. The voltmeter is a voltmeter and only has two leads (+12 volts and ground) so again +12 volts should come from the same wire that the tach operates from (or the same terminal on any other gauge. It has no sender. The voltmeter may have an "S" terminal on it but it should not be used -- just the "I" (+12 volt) and ground terminals are used. The gauges normally have an internal light so the "L" terminal is again jumpered from one gauge to the next and that terminal is powered from the NAV position of the NAV/ANC switch. Gauges normally peg when the "S" terminal is grounded. That tells the gauge there is very low resistance in the circuit which represents a full scale reading.

 

[Holy Shamolee]

Re: Can't get gauges to work...

This is the way it is wired. Exactly as you said and like the diagram
Even though it is a brand new engine and there is probably oil pressure i hate to run it for even a minute unless i can see oil pressure.
I took the new meter to the engine compartment.
I hooked 12v ti the I terminal.
Ground to the ground terminal.
The sending unit to the S terminal.
It started with 50 psi and pegged left back to 0 psi
it did this a couple times.
I stopped the engine and am still scratching my head.
It's highly unlikely, but could this sending unit be made for a light?
As I said, when I got the boat all the gauges were pegged to the right. Power on or off, the would not move. They have since returned to normal after I hooked up the new engine.
I wonder if someone has fried them?

There is a sticky at the very top of this forum (not this page) titled "Generic Boat Wiring Diagram). Study it and you will see that the only ENGINE related gauges are those that require senders. the tach sense comes from the ignition coil, the fuel gauge sender is in the fuel tank, the temp sender is on the engine as is the oil pressure. +12 volts for all gauges comes from the "I" terminal on the ignition switch. Ground is wherever you find it at the helm. Those two wires are simply daisy chained from one gauge to the next. If the tach works then follow the +12 volt and ground wires to each of the other gauges. The voltmeter is a voltmeter and only has two leads (+12 volts and ground) so again +12 volts should come from the same wire that the tach operates from (or the same terminal on any other gauge. It has no sender. The voltmeter may have an "S" terminal on it but it should not be used -- just the "I" (+12 volt) and ground terminals are used. The gauges normally have an internal light so the "L" terminal is again jumpered from one gauge to the next and that terminal is powered from the NAV position of the NAV/ANC switch. Gauges normally peg when the "S" terminal is grounded. That tells the gauge there is very low resistance in the circuit which represents a full scale reading.

 

[Holy Shamolee]

Re: Can't get gauges to work...

I went and bought a mechanical oil gauge and a tee.
Plugged in both gauges and started it up.
Idling the mechanical gauge gives me 50lbs.
Electrical was still screwed up
Went to the command bridge and unplugged all the purple wires.(the ones that go to the I on the gauges.
Went back down and looked at my gauges.
Everything was working except my water temp.
It is a brand new engine, and I seem to have some sort of air lock in it. I'm sure after I run it a while and the thermostat opens and things get flowing I can get rid of it.
Maybe then my water temp will work. It's not as simple as the other gauges to track down as it goes into my electronic ignition.

 

[glenn property of pam]

Re: Can't get gauges to work...

the electrical oil pressure gauge is connected to a oil pressure sender or a oil pressure switch? the sender which changes resistance with pressure is diffrent from a oil pressure switch and must be matched with the gauge. same as the water temp sender. no idea what you mean by un-plugging the purple at the command bridge then went down to gauges (do you have 2 sets of gauges on the boat?)

 

[Holy Shamolee]

Re: Can't get gauges to work...

Yes 2 sets of gauges.

 

[glenn property of pam]

Re: Can't get gauges to work...

ok well that explains why they dont work. oil pressure, temp, fuel gauge all have to be dual gauge sender units (they have half the resistance range of a single gauge unit). the other option is to install switch/switch's to transfer readings to the second set of gauges so only one set works at a time which is easy if you understand electronics but difficult to wire if you dont.

 

[Holy Shamolee]

Re: Can't get gauges to work...

All that is up top is Tach...which seems to be working. Water and oil.

Switches for oil and water might be within my capabilities.

 

[glenn property of pam]

Re: Can't get gauges to work...

if you are happy to have only one switch on the lower controls then a simple dual spdt switch will do just wire the sense to common then a wire going to the sense input on each gauges on top and bottom. one side of switch for oil one for water. if you want switchs top and bottom then thats easier with a relay. you are making and breaking the sense wire to the gauges (to stop the resistance change) not the ign wire as that will possible make the gauges read inacurrate. you can put in a power switch if you want to shut the other gauges down but it is not required.

 

[Holy Shamolee]

Re: Can't get gauges to work...

That sounds pretty simple. I can probably do that.
I still do not have my water temp gauge working though.
The wire goes from the sending unit to the electronic distributor.
That's the way the motor came wired.
Don't know why it goes there, Just complicates everything.
I like it simple.

 

[Holy Shamolee]

Re: Can't get gauges to work...

Please excuse my stupidity..(inexperience.
The sensor that goes into the ignition is a knock sensor.
No temp sender came with the engine.
Apparently in mercs it is in the thermostat housing.
I will have to get one or maybe i can take one out of the old engine.

 

[glenn property of pam]

Re: Can't get gauges to work...

they dont cost alot so maybe buy the dual then just get a dual for the oil pressure and job done both gauges will work