470 tach electrical- ground wire destination? And Positive side

[aarons 470]

Hello All.

I am rewiring most of my 1977 Cobia boat, and tracing the rest. It has a Mercruiser 470.

The Tachometer has three wires coming off of it studs.

One is pink or peach in color, connected on the positive side of the tach. I believe this goes to the coils positive side?

Then there are two ground wires. One has a common ground connection to the other gauges in the panel.

My other question is the other ground wire. It is a bigger wire, 10 gauge. It comes off of the tachometer brown, then goes to a harness behind the dash. After that there isn't a brown wire. So I am not sure which wire it is that continues.

Does anyone know where the larger ground from the Tach is connected to? Can i just ground it to a solid ground, or is there a special place it needs to go to in the engine area etc?

Thanks

 

[Don S]

Re: 470 tach electrical- ground wire destination? And Positive side

You should have 3 wires going to your tach. White is 12V+ from the ign. switch, Black for ground and a Brown wire to the + terminal of the coil.
Other white and black wires may spit off and go to other instruments as they are common for all the instruments. But the brown wire should be all alone on it's terminal.

 

[aarons 470]

Re: 470 tach electrical- ground wire destination? And Positive side

Ok, I may have a problem? So there are two studs on back of my tachometer.

One side says negative. Right now it has a small ground wire off it that ties in with all the other gauges ground wires. And there's also larger 10 gauge brown wire coming off the negative as well.

The Side marked with an "S" I am guessing that means switched power? So all i need there is 12 volts when key is turned? Right now it has one peach/light colored wire off of it.

I am wondering if i should just rewire all of this?

 

[Don S]

Re: 470 tach electrical- ground wire destination? And Positive side

The S is for sender.

Post a picture of the back of you tach, who knows what you have there, or who did what when on a 35 year old boat.

 

[aarons 470]

Re: 470 tach electrical- ground wire destination? And Positive side

The S is for sender.

Post a picture of the back of you tach, who knows what you have there, or who did what when on a 35 year old boat.

Ok, here is a picture

The blue wire goes to a bulb.

I marked the gauge in black ink with what it reads on the back. The thick brown wire goes into a harness behind the gauge cluster, and there is no brown wire out the other side. So not sure what it goes to.

I am not really sure where the light colored wire ends up either.

When i got the boat, i could hot start it from the solenoid "sometimes" and occasionally it would start from the ignition switch. Either way, when it started, the key wouldn't kill the engine. I had to turn off battery kill switch. So I figured i had a ground out somewhere due to the way it did different things. Or it was the solenoid, the ignition switch, maybe the starter? But it seems to turn over great when it gets the signal.

I cleaned basically every wire terminal, in dash and engine area. took out the old toggles switches, added a new toggle panel for the basic accessories which are working good now.

Replaced the ignition 4 way switch (only 3 terminals were used) with a new new brass basic 3 way ignition switch, the same way they had it connected. Not sure it was right, but I am assuming it was......

disconnected the stock charging system. Incase it was grounding out somewhere. alternator is going in this week.

after doing this, Still wont turn over from key switch.

Today i was poking my tester around the ammeter. I noticed the wire from the ignition switch marked "BAT" goes to the "NEG" side of the Ammeter. I thought this seemed strange.

When i turn on the ignition switch to accessory. The ammeter gets power to the positive side from a 10 gauge orange wire from the main engine harness. What i thought was weird, is the negative side of the ammeter lights up with my tester, Should voltage be going through the ammeter to the negative stud side? It isnt marked ground, so maybe this is normal?

I will leave it at that for now, one- or maybe 3 things at a time

I may have to get a manual for engines that just shows point A to point B for a basic engine

Thanks Aaron

 

[aarons 470]

Re: 470 tach electrical- ground wire destination? And Positive side

I forgot to mention, that i did replace the solenoid, and same result