I measured 4.98 and I did add a 1 amp load to it also. It needs 5.1 volts to work right. 7805 cant ever produce that.

 

You are correct, the the range of the gauge will be slightly off.

Increasing the voltage will increase the span of the gauge. The only gauge that actually has true values is the gas gauge. The other gauges have "normal".

The Mustang gauges are also non linear based on the resistance ranges of the senders and the gauge reading. Many people have issues when they change out the senders and have them indicate at a new point on the gauge.

Mine do read low as you suggest. A full tank shows as being 7/8 full and empty is a little below the empty line.

I have also installed electric gauges under the dash so I have redundant indication (with actual indications) for Volts, water, oil pressure and oil temp to be safe.

 

Have you checked to see if the plug connector did't become loose enough to cut the power but not enough for the plug to come apart.

 

I'll chime in and also recommend buying or making an electronic cluster voltage regulator. Those replacment ones are not very good.

 

I replaced the voltage regulator on the back of the instrument gauges and now my headlights and gauges dont work. It seems like the gas gauge is out of whack too. Any ideas on what could of happened?

 

Which one did you get? If you got a regular replacement one, that very well could be the problem.

I have had 2 or 3 of them and non of them worked right. My original one still works but the others all had varying issues. I have a home made electronic one now. I think that NPD and a couple other suppliers offer an electronic regulator.

 

I picked it up from Cj pony parts..

 

Was it this one? If so, it might be the problem, but I can't say for sure that it is.

http://www.cjponyparts.com/product.asp?pn=HW1566

 

yea i think thats the one

 

Do you have a multimeter? If so measure the output from it with the key on. See if if its high or low or erratic or nonexistant.