Voltage Drop from ECM?????

WARNING IF THIS POST DOES NOT CONFUSE YOU, then you are a more confused individual than I am and that may be scary.

Ok I was having voltage problems in my 88GT.  Dropping as low as 10.9v under load with the A/C and lights on, I had to rev it to 3000 just to get it up to 12.5. 

I added an extra ground from the battery to the block, and added an extra power power from the battery to the junction studs below the main connector near the battery. (sorry can't remember what it is called)

Voltage improved only slightly.  So I went and got a new Delco 105amp alternator.  I installed the new alternator and voltage on the Gage on the dash is good 14-14.8v, and voltage at the battery is charging at 14.1v idle.  However when I plug in the scan tool and watch the battery voltage readings from the ECM it is showing high of 13.8 with everything off and dropping as low as 12.8 when I start turning things on.  Idle with the A/C is 12.8v (from ECM) when the battery and dash are reading 13.5 with my proper Voltmeter.

This just seems odd to me.  I can't figure this out.  I checked the Main ECM ground at the base of the centre console under the ECM and it is good and solid.  I made sure all the ECM plugs were in solid.  I I am kinda stumped as where to start.

As a side note that may or may not have any implications.

My dash temp Gage when reading 104C (a tick below the middle) is reading on the ECM as 108C and the rad fan clicks on at 109C until the ECM See's the temp drop to below 105C.

So the Temp sender for the ECM  is either showing 4c high and the rad fan is coming on proper, or the dash Gage is right and both the ECM and Fan ON temps are wrong.

The Tach is reading 24% high.  As 2450 rpms in the ECM it is reading 3100 on the dash  I have just gotten used to reading it like that.  I am not sure which to believe the ECM or the Gage on the dash.

Anyone got any idea why so many of my gages and even ECM readings would be so wonky. 

I am going to talk to Watts about tweaking my chip that he made for me to better set it up for the up coming road trip Lisa and I are leaving on. 

sounds to me like you have a bad wire between the power and ECM which is bleeding current or just not getting it. Check the voltage at the direct terminal on the ECM. Could be a weak Capacitor in the ECM. Just a hint... I had a problem with my truck much along the same senario. Took me abit to find it but turned out to be a wire that had corroded inside the insulation 3 inches up from any terminals or junctions. What happens Dave, the crap they are spraying on the roads for deicing in the winter is "MAG". It is a highly concentrated sea-water. How it is made is by dyking tide pools and then letting the sun and air evaporate the water leaving behind the liquified salt. They repaet this for close to four years, reflood and evaporate. When it is finally used it is like a slime so you can imagine how corrosive it is. The worst thing about it is the way it travels inside wiring insulation, then attacking and corroding the wire. In most cases, the wire will appear a bit swollen and/or have the green colour of the corrosion present. I have found some to be a soft spot in the insulation and it feels quite easy to stretch. Just something to keep in mind as you hunt down the loss.