Still looking for help with tach and trim gauges?!?!

I have a 1993 Mercury 115 and I have been having problems with the tach and the charging system (read my other posts!!).
I narrowed my previous problem down to a voltage regulator, which I replaced. After doing that, the charging system worked and the tach worked fine for about 20min. I shut off the motor and restarted and now the tach doesn't work anymore. The needle moves up and down at random going a various speeds. The boat is still charging the battery.
I did the bench test on the new voltage regulator after this happened, and everything checks out but the grey tach wire. I am not getting any readings on it.
Is it possible that the tach part of the voltage regulator would fail while leaving the other parts to work properly and what would cause it to fail in the first place?

I then attached the grey tach wire right onto my terminal block (with a suggestion from Chris1956)where the yellow wire from the stator joins the yellow wire going to the VR and my tach still isn't working properly. Even when the key is off, the needle never falls below the 1000 RPM range and at WOT it goes into the 7000 RPM range which I know is not correct. Should I be getting an accurate tach by this method and if I'm not, does that mean that there is something wrong with my tach?
Also, my trim gauge doesn't work at all and I checked the resistence at the trim sender and it appears to be working properly. Could the tach and trim gauge be connected in failing to work?
I checked the voltage at both gauges with the key on and I am only getting 4.5v on each gauge. Should I not be getting 12v?

Any help would be appreciated.

Re: Still looking for help with tach and trim gauges?!?!

Both gauges require +12VDC and ground to work as well as a signal from their individual sensors. it is not unusual for a tach to freeze where it is when engine is cut off. However, when ign key is turned to run position, it should zero.

Fix the voltage to the gauges first. then see what works or doesn't

Re: Still looking for help with tach and trim gauges?!?!

Thanks Chris1956. I figured that I needed to have 12v at the gauges and that is where my problem lies. I will try fixing that and then go from there.

Re: Still looking for help with tach and trim gauges?!?!

Okay, I do have 12.17v at each gauge so that is not the problem. I cannot figure this out and it is driving me crazy!
My trim sender is working because I have resistance that changes when I raise or lower the trim, so I figure it is something to do with my gauge.
My tach is not working even though it is connected directly to one of the yellow stator wires and is bypassing the VR.
As an aside, the tach is zeroing when I turn the key on.
I am about ready to give up and just live with the gauges not working.

Re: Still looking for help with tach and trim gauges?!?!

Not sure what to recommend. Can you look up the trim gauge brand and see if it is compatable with the sender? I presume the sender is Merc? It will have a particular resistance range. Maybe the gauge doesn't work in that range.

See if you have some AC voltage on the stator (to ground), with the motor running. If so wither the tach wire is grounded somewhere, or the tach is bad.