View Full Version : Tach

07-13-2011, 09:18 PM
OK, Tach bounces around when I turn the key on. It never resets back to zero with the engine off. Any Ideas?

07-14-2011, 05:11 AM
Sounds like a bad ground. Does the needle still move when you increase RPM?

07-14-2011, 06:46 AM
Yes, and where would the ground be because I checked the plug in the back of the tach and it's fine.

07-14-2011, 07:48 AM
What kind of tach is this? (original or aftermarket)
You should have 4 to 5 posts at the back of your tach:
Ground = black (this is usually coming from the ground post of previous gauge and going to the ground post of the next gauge)
Send = gray (this is the RPM signal coming from the coil)
positive = red or purple power when ignited
LT= This is switched post for the backlight of the gauge (only on with nav lights) sometimes there are two connections here

Your ground might be connected properly at the back of your tach but since its connected to the next gauge and then on to the next gauge etc, any faulty connection/corrosion along the line could cause the problem. I would try diconnecting the tach ground from the other gauges and run it directly to the battery ground and see if the problem remains. If the problem goes away you've found the culprit.

BTW: on most gauges the needle only really goes back to zero when you turn the key, just before cranking.

07-14-2011, 08:08 AM

I am going to have to try to just jump the ground to see if it helps. And that is when i check everything, I turn the key to the run position, let the gauges reset, then look at them.

Thanks for the advice though, I will check it hen i go home from work today.


07-16-2011, 10:53 AM
I've been having some issues with my guages too. At first I had nothing and I was able to come across an earlier article that helped me out to this point.

Refering to: http://www.mastercraft.com/teamtalk/showthread.php?t=31131
I went ahead and replaced the MMDC under the dash and that gave me all of gauges back except for two, tach and engine temp.

I've hooked a computer up to the engine and was able to read both signals but the gauges are not showing what I'm seeing on the computer. I've got a 2001 and the engine electrical harness was definitely showing some wear, I replaced the harness thinking that it might resolve my issues with the tach and engine temp but no luck.

Any suggestions? If the gauges are bad, which I'd imagine could definitely be the case, will Medallion repair gauges or am I looking at having to buy new gauges to replace the bad ones?

07-20-2011, 05:35 AM
Ever solve your tach issue V? My teleflex tach would only ground through the LT post. Finally opened the gauge and grounded it from inside: working now

07-20-2011, 06:42 AM
No, it's intermediate, I think I might have to do that.