Ignition mystery and gauge questions

[thebishop]

I am in the process of putting back the gauges and fittings taken off when painting my boat. In the process I needed to disconnect and reconnect the gauges. It is obvious the boat was rewired prior to me owning it. Seems simple enough, I do so first attaching the tachometer. All seems fine turn the key to the first position everything lights up. Proceed to rewire the rest of the gauges. Turn it to the first position, nothing. No lights, no trim or tilt. Mind you have not touched any wiring to do with the ignition or binnacle. So begin to trace wires.  Battery working fine feed off battery switch is allowing panel connections to work, just no power to gauges or engine despite their being power going into as affirmed tracing line back to engine using a voltmeter. So I assume must be something with the ignition switch, trace wires and realize nowhere, that I can see is the ignition attached to the battery. Both the harness into the back of the tachometer and ignition harness go straight into the bilge from the center console back to the motor. I have an E-tec with a magneto switch, not sure if that is relevant. At this point I am  confused to how the motor ever turned over before. Specifically, how was it ever getting power to the harness that go to the tachometer and ignition? Did I cut a wire or not reconnect one when wiring the gauges that somehow feed the whole system, pane aside.

I change the ignition rewire attaching the same  wires to the same terminals on the new Sierra ignition. Still does not turn over. At this point I disconnect the connection for battery on the ignition and run a wire from the battery switch to the corresponding connection. I get power, but the trim tilt still do not work. I reattach the old battery wire along with the new one and now everything is fine. I have power to the gauges and the trim is working.   Has anyone every heard of  a wiring something like this? It is obvious that the old battery connection is also feeding the binnacle, is that normal? I am concerned I am going to screw something up by doubling up on that connection.

Moreover, the gauges which are not lighting up. So i switch around what the grounds and hots which I assume were improperly wired when it was rewired before I touched it. Now they light up but are pinned to the top and the battery gauge does not work,  with the exception of the light. Tachometer appears to be fine. Again power source seems to be coming from engine and nowhere are the gauges connected to the battery.  From what I have thus far read the power for the gauge lights should be coming off the navigation switch. Is it as simple as leaving the tachometer connection and  monitoring feeds to the gauges in place, and wiring the light from the navigation lights? If so, it appears there is a power source feeding the gauges from the harness behind the tachometer, do I need to be concerned with having an additional power source? As I assume the harness behind the tachometer is now providing power to them. I am  confused by this and the last thing I want to do is  screw something up. Any help would be greatly appreciated.

Thanks,

Greg

[seabob4]

Greg,
First, assuming you have standard analog gauges with the "SystemCheck" function in the tach.  Now, this is how gauges work.  They get their power through the engine harness, as well as the tach sender, which is the gray wire.  The purple wire is the 12V+ from the harness.  With the key in the off position, their will be no voltage on the purple.

Now when you switched hot and ground, the gauges were getting power, but reversed.  The "pegging" of the gauges shows that the ground to them was incorrect.  Fuel gauges, for instance, will peg to full if the ground is bad or missing.  So that explains that.

As far as the ignition attached to the batt, well, yes it is, just not directly.  You'll notice on the positive terminal on the starter motor (which IS connected to the batt), there are a couple of other smaller (16GA) wires terminated there as well.  One of those is the red wire in the harness that goes to the ignition switch.  So, yes, the switch is attached to the batt, through the motor.

And as far as the gauge lights, yes, you are correct, they should be wired to the nav lights.  Nobody needs to have their gauge lights on during the day.  On many of the boats I re-wire, particularly Yamahas, the gauge lights will be energized by the ignition hot.  Just a matter of disconnecting the blue wires from that source and pulling power from the nav light circuit.

[thebishop]

Thank you so much.
One thing I am not clear on is does this mean I should not be jumping the ignition straight from the battery?

[seabob4]

Thank you so much.
One thing I am not clear on is does this mean I should not be jumping the ignition straight from the battery?

While that won't hurt anything, there should be no need...unless the ignition feed in the engine harness has gone bad, i.e. broke, or whatever.  12V is 12V, no matter where it's source of origination is.  That's what the ignition circuit wants...

[thebishop]

Bob-

First, thanks so much for the help.

I know the 12v + wire, should provide power, but it doesn't. It does, however, still control the trim/tilt.   One other question, while the electricity is now  properly wired to gauges with the exception of tach and tilt  I cannot get any reading on my gauges. Does this have something to do with the I labeled spades on the gauges? Interesting the hot purple while which is connect through the key is attached to the last gauge, the trim  which seems weird. If I want to put the lights on a switch would I remove that feed and wire it from the panel purple into switch at panel? Or is that wrong.

Greg

[GoneFission]

Trim/tilt is not powered from the dash - it comes from the engine and the up/down switch just connects the solenoids on the trim unit.  Sounds like you have a positive feed problem - could be corrosion or a broken lead.

[seabob4]

OMC gauges are wired, typically, where the purple from the engine harness goes to the "I", or ignition, post on the tach, then daisy-chains to the remaining gauges.  All this lead is doing is suppling power to the gauges when the ignition key is in the "run" position.  The Tach sending lead (gray) provides the tach signal, the trim sending lead (brown or tan) provides the trim signal, and the fuel sending lead (pink, from th hull harness), provides the fuel signal.

The backlighting circuit is independent of the gauge save the ground.  Daisy-chain the positive (blue) and tie it into your nav lgt wire (gray).