View Full Version : Tach Chatter, gauge cutout, and MDC controller

07-11-2008, 12:15 PM
I replaced the MDC 1600 controller in my 99 Mobius a couple years agobecause it had water in it. Since then I have had sporadic behavior of the gauges. I will start it up and everything does what it is supposed to, then after a few minutes all gauges quit. After that a variety of things seem to have an impact on getting them back.

1. Shut it off and add gas.
2. Crawl under dash and press all connectors on controller and circuit board to make sure they are snug.
3. Sometime just shutting down and restarting.

The only things these have in common is shutdown - startup. So I started thinking it might be tied to the ignition switch. While I was under the dash and testing to see if pressing connectors helped I turned the key and noticed that the rattling sound the gauges make when they all fire up only happened when the key was in the right place. So thought it might be somehow tied to the ignition and the ground that it creates. And that maybe different people apply different pressure to the key and that maybe some do not turn it far enough??

The other thing we noticed is that the Tach makes a lot of noise when running normally. If you put your ear on it while the motor is running it is quite loud, and erratic. The erratic nature seems to cause unsteady behavior of the needle. Not huge - but detectable.

Any thoughts? Maybe a bad ground in the tach causing prolems for the controller in general?

07-17-2008, 12:44 AM
This has been a pretty busy group so I thought I would touch this and raise it back to the top of the list in case someone with input might have missed it ..

Heading back up to lake tomorrow so any response between now and 16:00 tomorrow would be great ..

07-28-2008, 01:59 PM
Anybody ?? I thought this had been dealt with by simply wiggling wires. But it just hit me again. I guess the good nes is that the hour meter seems to also be impacted - so the boat is not aging as fast.

But if anyone has input I would really appreciatre hearing. Right now I am running with GPS and do not have oil or temp gauges....


08-05-2008, 10:35 PM
Hey same issues here... The guages don't work at all though. It's a 2002 Moomba Mobius V-drive with the carbed 310 Assault. I've checked the connections and looked to see what the voltages are from the guage harness to each individual guage. They look to be all different readings. I've read something about a small black box that converts the readings to the circuit board and into the guages. The boat actually stalls randomly and havn't a clue what the issue is!!!

08-05-2008, 10:52 PM
On my boat the black box is the MDC 1600 controller. I have already replaced that once due to water in the unit, presumably from a break in the spedo transducer. I am thinking in this case that the tach may be causing general grounding issues that are effecting all the gauges, but was hoping for more help from the crowd. ....

08-06-2008, 06:04 PM
When the tach flunctuates do the other meters fluctuate also? Sounds like a floating ground problem or resistance on your positive lead to the controller. I would recommend running a jumper from the fuse panel to the controller for both the ground and positive wire. If that corrects the problem then the wiring needs to be redone.

08-07-2008, 01:42 AM
I am reluctant to get into that wiring harness. Can I run a parallel ground from tach to battery, i.e., just a stray wire without going through the circuit board? Or maybe replace the tach if there is an internal ground issue with the tach? The other gauges do not seem to have the same chatter thing going. But about once every week or so the gauges will quit for a couple of passes, maybe half a day. And then they start working again. Maybe it is heat/moisture sensitive? Need to pay closer attention to temp and humidity when it occurs.

08-07-2008, 12:13 PM
Funny, after my message I took my boat out and I had instrumentation issues after I turned on the bow light. The water temp gauge jumped about 10 degrees and when I turned off the engine all of the guages pegged out until I turned off the bow light. I have yet to find the controller on my 98 Mobius so I'm not sure if I have one but I do know I have a floating ground on the instrument cluster. For your situation, I would connect a ground to the tach and see if that works. The problem with the instument cluster is the grounds are connected together and somewhere the attachment point to the battery ground has resistance so the easiest path for current to flow is through light bulb filiments to ground so you never have a full 12 volts to the components. Adding a wire from the battery grounding block to the components would alleviate a lot of issues.