"Jumping" engine gauge displays

Claygr1 · June 09, 2008, 08:41:36 PM

So, our 1989 C34 has developed an interesting problem. While the engine is running, all three gauges (tachometer, temperature and voltmeter) will "jump" forward every three to five seconds. They are perfectly synchronized. It is a momentary jump forward and then back. The movement is not particularly large but it is noticeable. The frequency appears to be increasing as we've operated the engine the last several times. Has anyone experienced something similar?

Stu Jackson · June 09, 2008, 11:35:42 PM

Do you have an autopilot and is it on when this happens?

Tom Soko · June 10, 2008, 10:32:53 AM

Has the wiring harness been upgraded? It sounds like a bad ground to effect all three gauges at the same time.

Claygr1 · June 10, 2008, 12:07:18 PM

I made an error in my original posting. The tachometer does not "jump." Only the temperature gauge and the voltmeter move.

We do have a newly-installed S1 Wheelpilot but the condition has occurred before installation and after installation. It also happens with and without the autopilot engaged.

In answer to the wire harness question, the answer is sort of. We don't have the molded rubber plug connections. PO or his designate replaced those with butt connections. I spoke to Seaward about this last winter and they recommended moving to the termstrips. The wiring does not look to be in great condition (no doubt original to the boat) so we ordered the wire harness and the termstrips from Seaward this spring. It is on the list of things to do this summer.

Jon Schneider · June 10, 2008, 12:37:34 PM

The question is, was the orange battery charging wire (from alternator) re-directed from a full loop to the panel and back to the starter, or is it still configured to send the alternator output through the panel. If this is the case (or even if it's been corrected), it is quite possible that you've developed a short in your panel wiring, especially around the wires connected to the ignition key terminals. Take the panel off (just pull it back after unscrewing) and examine the condition of the wires very carefully. It could be that a couple of wires are beginning to meld together (happened to me) causing intermittent (but soon to be constant) shorting.

Stu Jackson · June 10, 2008, 02:27:01 PM

Jon's point is well taken. You need to know your wiring. That old orange wire connecting the alternator output and starter may have been changed by a PO so that the starter was only connected to the 1-2-B switch for power and the alternator output either sent directly to the house bank or still back to the switch. I say this because on our old 1986 boat, there were two wires (#4) to the C post on the 1-2-B switch, one from the alternator and one to the starter. Usually there was only one with the small orange wire going to the starter from the alternator. My guess for the reason for this is that the PO had installed an Auto Mac voltage regulator. There's another orange wire that goes all the way back to the panel, so we may need to be more specific about which orange wire we're talking about. To be any more specific without seeing your boat and its wiring is difficult, so let's leave it up to you.

In order to grok this, you may want to go to Projects (click on the link at the top of the MB page) and scroll down to the Engine Wiring Harness link and read it and the wiring diagrams with it.

One suggestion: many panels are mounted differently, so be careful before you just unscrew it. I've seen some where it's easy to get off because the screws on the outside white support are just sheet metal screws holding it all in. Others, like mine, have machine screws holding the silver panel itself into the fiberglass. If you just back those screws out, you'll lose the nuts behind the panel. Check out how it's screwed in first before you remove any screws.

Ron Hill · June 10, 2008, 06:09:38 PM

Clay : The only thing that will make the temperature gage "jump forward" is that it's being grounded out and then ungrounded! I installed a "Hi Temp press to test" and that's what it does intentionally (so I can hear the alarm sound)!!
Not to sure about the V-meter.

Claygr1 · June 11, 2008, 04:18:20 PM

Thanks for the ideas. It sounds like we're moving the replacement engine harness up in the priority list. Another no doubt simple and naive question - where do you mount the termstrips at each end? One of the schematics in the project section suggests that there is a fiberglass housing behind the engine panel. I know that we have no such housing. Behind the engine panel, there is nothing but air and then hull.

Ron Hill · June 11, 2008, 05:16:42 PM

Clay : As I wrote up in the Mainsheet (with pictures), I put mine in small "Rubbermade" boxes so I could snap on a lid. I cut one inch holes in the side with chaff guard to protect the wires. The lid keeps the wire connections protected from shorting with any others and keeps any dripping liquid out.

With all that said, I just had to remove/reinstall the engine from the boat TWICE and both times I disconnected all of the wires from the engine -- SO, I didn't use the connectors that I had installed!!
You might want to "hard" wire and just solder (then cover with heat shrink) those connections. It's a lot easier than those "euro strip connectors". Wish I would have done that, now that I know it's easier to disconnect all of the wires from the engine anyway!!!!!! A few thoughts.

Jon Schneider · June 11, 2008, 05:53:42 PM

Quote from: Claygr1 on June 11, 2008, 04:18:20 PM
where do you mount the termstrips at each end? One of the schematics in the project section suggests that there is a fiberglass housing behind the engine panel. I know that we have no such housing. Behind the engine panel, there is nothing but air and then hull.

You don't have to attach the termstrip to anything, but it would be better if you could attach a cable tie to something solid around both ends of the harness wires near the termstrip. In the engine compartment, I screwed the termstrip to the wall adjacent to the head. Regarding the panel housing, there might be an additional fiberglass cover behind the panel on newer boats, but on mine (year 1990), the housing is the recessed unit that the panel mounts into with nothing behind it (and I just bought a new housing, and it didn't come with any backing).

Stu Jackson · June 11, 2008, 08:48:20 PM

If you look at the gif files in the engine harness Seaward article, they show the two parts of the cockpit panel: the silver faceplate that holds the actual gages in place and the white "enclosure" around it (with the clear plexiglass faceplate in front of those two parts). See: http://www.c34.org/projects/images/harness/harness2.gif

That enclosure IS the "housing." The termstrips float in thin air, held up by the wires themselves, just like in the sketch. And at the engine end, too.