Wiring help/Electronic gauge

[nola mike]

Went ahead and bought this gauge mostly to replace my speedo with a GPS unit. I'd also very much like an accurate tach as well, as I have a new engine and am trying to dial in my carb and prop. This also comes with voltmeter, fuel gauge, oil pressure, and temp capabilities. Haven't taken it out on the water yet, but have some questions about the wiring:
1. Is it (hopefully somewhat easily) possible to have the electronic gauge and my analog gauges peacefully coexist? I'm guessing the electronic gauge is sending 12v down the sender and comparing the voltage drop to a reference 12v signal, but not sure. Different than an analog gauge though. I don't want to add an additional sender and wiring for OP, fuel, and temp, but didn't know if there was another way. Not the end of the world if not, but I don't like the gauge flashing "0 psi" at me.
2. Bigger issue: Wildly fluctuating RPMs. There's a calibration setting on there, which I'm trying to figure out (the instructions are wrong), but either way I don't think it would account for the fluctuations, would it? Initially I wired it into the lug for the analog tach sender. Then tried disconnecting the gray sender wire and connecting it directly to the new gauge. Finally ran a wire directly from the gauge to coil neg. None of it made a difference.

The gauge is actually pretty cool for the $75 I paid for it, and probably still worth it for what I paid, but I'd like to get all the functions working if possible, and redundancy is always nice.

Video:

 

[nola mike]

Anybody have any thoughts?

 

[nola mike]

TL;DR Could I splice the gauge input into the grn/wht wire from my TB IV module? @achris ?

Long version:
OK, so I contacted the gauge seller, who told me that the gauge won't accept a coil neg input. He said it would take the input from a regular magnetic 2 wire sensor, which he offered to send me. Problem is that it needs to take the signal off of the flywheel somehow, needs drilled into the flywheel cover, etc. I'm trying to figure out another solution. They have some fairly pricey (~$100) boxes that might work, but still not very elegant, especially for a $80 gauge.

 

[achris]

TL;DR Could I splice the gauge input into the grn/wht wire from my TB IV module? @achris ?

Possibly. The wht/grn (not grn/wht ) is a 0 to 5v signal. I would try it and see (unlikely you'll hurt any of the Merc electronics. Remember that wht/grn gets grounded by the shift cut out)..

1. Is it (hopefully somewhat easily) possible to have the electronic gauge and my analog gauges peacefully coexist? I'm guessing the electronic gauge is sending 12v down the sender and comparing the voltage drop to a reference 12v signal, but not sure. Different than an analog gauge though. I don't want to add an additional sender and wiring for OP, fuel, and temp, but didn't know if there was another way. Not the end of the world if not, but I don't like the gauge flashing "0 psi" at me.

Had a look at the gauge specs with the link you included. It will not be possible to jump off the existing gauges. You will need to pull a new multicore cable for the senders, and you'll need additional senders. Even if you connect the new wire to the existing senders effectively in parallel, they will not play nice with each other. This guage is a completely standalone system to the Merc gauges. Nothing you can do about that. Merc do make 'dual station' senders, but that would only work if you can configure the multi-gauge to accept 'standard' input values, and from what I can see, the only input that is standard (33-240 ohm) is the fuel gauge. If you don't want to run a new cable(s), then if you can configure the new gauge for 33-240 senders you could use it INSTEAD of the Merc analogs.

Chris......

 

[sam am I]

The front end of the tach could be being over driven, but I also think your tach is just picking up the varying freq's from the "ringing" that occurs when the coil is switching off and on, its sample rate is such that it's displaying various area's of the ringing. I think they're real just not needed, the tach just needs to have it's signal averaged better.

Add a resistor (maybe around 10K) in series with the tach on it's signal wire (gray usually) will not only reduce the signal level (if it's being over driven), it will also form a better averaging filter using the inherent capacitance of the gauge HOWEVER, if we need more filtering/averaging, a external cap to ground on the tach side of the resistor also can be added.

 

[nola mike]

Possibly. The wht/grn (not grn/wht ) is a 0 to 5v signal. I would try it and see (unlikely you'll hurt any of the Merc electronics. Remember that wht/grn gets grounded by the shift cut out)..

Had high hopes for this. After hooking up and then trying to figure out why the engine wouldn't start (gee, maybe it's that new electrical connection, dumbass), it looks like the gauge somehow grounds out this wire. Wish I had a DSO to figure out what's going on, but was getting about 2.5v off of WHT/grn and 10v off wht/red. I tried reading hz off the wht/grn, but that also killed spark--not sure why. I neglected to see if engine speed changed the voltage from wht/grn, but I can't imagine the module doesn't send some type of pulsed signal to the amplifier.

Had a look at the gauge specs with the link you included. It will not be possible to jump off the existing gauges. You will need to pull a new multicore cable for the senders, and you'll need additional senders. Even if you connect the new wire to the existing senders effectively in parallel, they will not play nice with each other. This guage is a completely standalone system to the Merc gauges. Nothing you can do about that. Merc do make 'dual station' senders, but that would only work if you can configure the multi-gauge to accept 'standard' input values, and from what I can see, the only input that is standard (33-240 ohm) is the fuel gauge. If you don't want to run a new cable(s), then if you can configure the new gauge for 33-240 senders you could use it INSTEAD of the Merc analogs.

Chris......

Yeah, it works fine instead. Was hoping there would be an easy solution by using a dual station sender and some resistors or something. When hooked in parallel the analog gauges work correctly and the electronic gauge didn't read anything.

The front end of the tach could be being over driven, but I also think your tach is just picking up the varying freq's from the "ringing" that occurs when the coil is switching off and on, its sample rate is such that it's displaying various area's of the ringing. I think they're real just not needed, the tach just needs to have it's signal averaged better.

Add a resistor (maybe around 10K) in series with the tach on it's signal wire (gray usually) will not only reduce the signal level (if it's being over driven), it will also form a better averaging filter using the inherent capacitance of the gauge HOWEVER, if we need more filtering/averaging, a external cap to ground on the tach side of the resistor also can be added.

I had thought of this, that if I could somehow change the sampling rate that that might work. Strangely (I think?) with the dmm on hz measuring from coil neg that was also all over the place. That was coil neg -->ground. Thought I might get a reading going across the coil but didn't want to fry anything.

At this point I'm keeping the gauge, and I'm going to get that damn tach working at least. I'll try the resistor, though don't know where to get one these days without radio shack...
So would the resistor just attenuate all the signals and essentially just let the tach pickup only the strongest? The cap I understand would act as a high pass filter? I have no idea what kind of capacitor I'd need.

 

[sam am I]

That was coil neg -->ground. Thought I might get a reading going across the coil but didn't want to fry anything.

The tach's sig SHOULD be taken from the neg side of the coil as that is the side that is switching and creates the sig. Recall the points (mech or electronic) open and close the neg side of the coil to ground while the pos side is tied to 12V. Each time the points open (after being closed), the coil's secondary side get an induced voltage (20KV for example) and fires a plug..........This switching is a pulse train is the RPM sig AND is what you want to read. HOWEVER, it is noisy as all get out as you're discovering.

"I'll try the resistor, though don't know where to get one these days without radio shack..."

I tear things apart and steal parts sometimes.....Got and old printed circuit board out of a Radio? Dishwasher? A/C unit? Anything? I save too much junk perhaps because I'm too cheap

"So would the resistor just attenuate all the signals and essentially just let the tach pickup only the strongest?"

Yes........In combo with the gauge's inherent capacitance, It forms a low pass filter and will average (integrate) the DC pulses.

"The cap I understand would act as a high pass filter?"

No, the cap(inherent or added and AFTER the added series resistor) to ground forms a low pass (you want to filter/attenuate high ringing freq's and pass low freg RPM pulses). What essentually happens is the RC filter network will strip off the high and leave the low.

"I have no idea what kind of capacitor I'd need."

Start with .1uf, ceramic or mica would be fine, by default they'd be 50/100V

 

[sam am I]

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