Tachometer issue, 2003 Larson 210 LXI

[eskimo2k]

I recently purchased a 2003 Larson 210 LXI with a 5.0 VP GXi motor. Boat has just 227 hours and is in beautiful condition, other than the tachometer not working. After trying the "Faria Rap" (aka, smacking it) and getting no results I started troubleshooting. The gauge is getting 12v at the BAT connection. When turning the key the gauge doesn't jump at all and looking at the Faria troubleshooter that's a pretty good sign it's bad. The ground wire is shared with other gauges that are working so more evidence this gauge was the problem. Tonight the replacement came, I dropped it, wired it up and when I turn the key to on the gauge needle jumps to 0. When I start the boat though the gauge just sits there. Turning on the nav lights the gauge does light up. And yes, the new one has the little dial set to 3, for 8cyl motor.

This was the gauge before I removed any wires:

3 purple wires are wired to BAT and 3 black wires are wired to GND. The two wires on the spade terminal are plugged in at the top of the gauge and on the gauge itself that terminal is just bridged down to the GND terminal that the 3 black wires are connected to. 2 of the purple wires are just jumpered to the gauges to the left and right of the tach and get 12V when the key is moved to on. The 3rd purple wire goes into the harness and I can't tell where it goes from there (harness is buried under the dash). It shows 0v with the key off, on or the engine running. A very similar looking purple wire re-appears in the engine compartment and plugs into the alternator.

A couple things confuse me here.
1. Why is there nothing connected to the SIG terminal.
2. I assume this 3rd wire should be giving some kind of signal.
3. Attaching this 3rd wire to the SIG terminal makes no difference.

I disconnected the purple wire from the alternator (it has a snap on weatherproof connector) and tried to probe for voltage at the plug on the alternator and found nothing.

Any suggestions where to go next?

 

[Silvertip]

The SIG terminal is connected to the Ignition system (coil). These are the pulses the tech counts to determine engine rpm. So yes there needs to be a wire on that terminal.

 

[eskimo2k]

I thought the same thing, but I don't see a disconnected wire anywhere around the tach. Anyone have a picture or wiring diagram of where the signal wire attaches to a 5.0 GXI at the engine? Hoping I can identify it by color/stripe and find it in the harness under the dash. Worse case I'll run a temporary wire and just see if that gets the tach responding.

 

[GA_Boater]

If Larson followed the ABYC color codes back in 2003 and owners haven't made changes, the tach signal wire is grey. iboats has a color code chart in the How To library - http://www.iboats.com/basics/marine_wire.html

I see one grey in the bundle under the tach and maybe some more about 7 or 8 o'clock by the tach.

The color code is not for engine wiring.

 

[eskimo2k]

Thanks for the chart, that's great. This isn't the first time I've seen someone say the signal wire is generally gray too. I went home on lunch and started looking for any wire that could reach the tach that was disconnected and couldn't find anything. I did however find this which looks pretty suspect:

That's clearly a couple ring terminals bolted together with some shrink wrap. They look really out of place the way they're coming out of the harness and are pretty much the identical length of the other wires that run to the tach. Step one tonight will be cutting off that shrink wrap and seeing what's going on there, what the motor/other gauges do when I disconnect those two gray wires and see if I'm getting any signal off of either of them.

 

[eskimo2k]

Between bad weather and picking up a new puppy last weekend I took a while to get around to investigating that shrink wrapped gray wire. Last night finally pulled the boat out in the driveway and dug into it. Under the shrink wrap was a philips screw and a nut holding two ring connector gray wires together and it didn't look factory at all. First thing I tried was separating them and seeing if all the existing gauges still worked, which they did. I then started the boat up and tried touching one to the tach signal lead, and the tach jumped to life. I took that one off and attached the other one, tach did nothing. I wired up the original tach just to see if it was actually fine but it was indeed dead. Decided to attach both gray wires to the signal terminal since the boat had been running perfectly with them bolted together and I didn't feel like trying to trace the single wire through the massive harness. Tach works perfectly now, though I only revved it a little bit since I was running on the flushing port with a hose.

My theory is someone attempted to troubleshoot the bad tach and then couldn't figure out where the wires were supposed to go. They then came up with this bolted together and shrink wrapped idea to cover up their mess? Who knows. I'm just happy I have a perfectly working tach again. Now the question is how long before my OCD kicks in over the RPM gauge not being a perfect match with the rest of the gauges (it's really close) and I ship the original back to Faria for a rebuild.

Thanks for the help. Definitely wanted to update the board on the resolution in case someone finds this thread with a similar issue in the future.