want to add temperature guage to 1978 SSV-177

[Neutron68]

I posted this question on another Glastron forum and got some responses, but none of the responders were sure.
The boat is up at the cabin, so I can't crawl under the dash and look.  When I can, I will.

This particular SSV-177 does not have a temperature gauge, just and idiot light labeled TEMP.

I found a temp gauge of the same vintage as the rest of the gauges in the control panel and I'd like to put it into one of the unused gauge locations.
(see below)

Is there an easy way to get the old gauge blank out of the panel? 
Or do I need to use a hole saw to remove it?

Eric

[75starflight]

You should not need to use a hole saw to remove it. There should be a U type clamp holding it to the dash with 2 nuts holding it to the gauge. remove the nuts and the clamp and it should pull towards you when sitting in the seat to remove it.

[V153]

Yeah, I would think it'd be anchored like Brandon says. Should be a big deal to remove'n replace?

[Neutron68]

I hope you're right! 

I'll report back once I have a look at it.

Eric

[Bayflite73]

I have the same dash with the same only sort of helpful light. That's a great idea!

[Neutron68]

I looked at the back side of the instrument panel this weekend.

The is no removable plug.  The whole panel is 1 solid piece of molded plastic.
It looks like each instrument had a hole cut and it was dropped into the hole.

See the photos:







Hole saw?

[Hyperacme]

Yep !

[75starflight]

Yep !

I agree, but I would first see if I could remove the dummy gauge face first so you get the proper size hole cut to insert a gauge.

[Jason]

I remember drilling mine to install a tach on my 74 V173. Just find a fine tooth hole saw and take it easy.

[Neutron68]

I remember drilling mine to install a tach on my 74 V173. Just find a fine tooth hole saw and take it easy.

Was your V173 dash built like the SSV-177?
Was there a gauge plug or gauge cover to remove?
Or did you just have to drill and hole-saw?

Eric

[Jason]

There was no plug. It had this metal cover to look like a gauge but it was just the molded plastic and wood behind it. yep, used a hole saw.

[Neutron68]

I finally found out how it was built!

There is a plastic dummy gauge (like a drink coaster) glued into the circular depression in the solid plastic dash.
As advised, I tried to pry the plastic dummy gauge and it did come off with some effort.

After that, the2 inch hole saw took less than 10 seconds to cut through the plastic dash.

[75starflight]

Very nice!

[Neutron68]

WEIRD!

When I got the temperature gauge connected up with JUST the input (purple) and output (tan) of the indicator needle coil, it was working normally.  I got a reading on the temp scale.

But, after I connected up the power and ground wires for the light bulb (which I expected would be a totally isolated circuit), the gauge reading dropped off the scale - zero or below!

When I measured from the needle input to ground resistance, I found 500 Ohms, where I expected an open circuit!
When I measured from the needle output to ground resistance, I found 400 Ohms, where I expected an open circuit!

Now, I'm wondering if I have a bad temperature gauge or if this is normal temp gauge behavior?

See the drawings of what I expected and the reality of this gauge.

[Rich_V174SS]

Purple is your 12v+ power from the ignition key switch, black is ground. Tan is the sensor wire from the temperature sender on the engine. The gauge only needs these 3 wires to operate. When cold the gauge should read at the low end of the scale when the key is turned on. To test the gauge momentarily jump the ground and sensor wire terminals on the gauge together and the needle should peg to the other extreme end of the scale.

[Neutron68]

Purple is your 12v+ power from the ignition key switch, black is ground. Tan is the sensor wire from the temperature sender on the engine.

You are correct on your wire colors.   I don't think the black ground wire should be connected to the gauge's needle coil inside the gauge housing.  I think the ground screw is only for the light bulb's ground connection.

When cold the gauge should read at the low end of the scale when the key is turned on. To test the gauge momentarily jump the ground and sensor wire terminals on the gauge together and the needle should peg to the other extreme end of the scale.

I can't perform that test for a week or 2.  The boat is 80 miles away from my house, in the city.

Here is what I think the internal connections of the temp gauge should be:


When I disconnected the ground wire from the gauge's ground screw (only the purple and tan wires were connected), the needle would deflect and give a reading, with the ignition turned on - expected operation.

Can someone measure the resistance between the connections of a known-good temperature gauge for me?
Check to see if the ground screw is connected to anything other than the light bulb.
If the ground screw is connected to anything else inside the gauge, how much resistance between the ground screw and the other connection?

Thanks!
Eric

[Hyperacme]

The " 70's Stern Drive & Jet " owners manual has a wiring diagram in it ...
Might help ...

http://forum.cgoamn.com/index.php?topic=2919.0

[Neutron68]

I think the mystery has been solved!

Rich was right - the gauge does need the ground wire to operate properly.

I wrote to the makers of Teleflex gauges and asked how it's wired inside so I could compare to the unexpected readings I took.
The answer is that there are 3 coils inside, not just 1! 
The other 2 coils account for the resistance readings I saw between the Sender terminal to Ground terminal and between the Ignition terminal to Ground terminal.

Given that the lowest temperature on the temperature gauge is 100F, the behavior I saw where the needle sucked downward off the scale is consistent with the 50F temperature of the boat engine in the 50F garage.  I just never expected the needle to go out of sight.  I expected it would just stay near the bottom like it does with no power applied.

Here's the explanation:

I can tell you that temperature gauges usually have 3 coils in them. One coil is the across Ignition and Ground and two coils at a right angle from each other are across Sender and Ground. What happens is that the magnetic field created by the "I" and "G" coil is acted upon the field created by "S"
and "G" coils which change depending on the voltage drop of the sender resistance, this magnetic field acts on the pointer driving it the position it was calibrated to.

If you look at the front of the gauge and were able to tilt it to see the very edge of the dial internally you would see 2 small dots near the edge, there would be a total of 3 groups of them. They were used to verify calibration at the factory prior to having the sealed from the front. You can connect a resistor across sender terminal and ground to simulate the sender and check the calibration to see if the gauge is functioning, please also remember to attach power to "I" and ground to "G". The resistance values are below:

300 ohms - 100 deg F
100 ohms - 160 deg F
30 ohms - 200 deg F

I have also included a .pdf file on the way to test the gauges that is the easiest. I hope this clears everything up for you.