i have a turbo 2 in a 1st gen with 2nd gen alternator and volts are good with nothing (13.8v) on but when fan turns on it idles funny and is at 12.88 volts. when i turn the lights on it dips to 12.08 and then starts to go down little by little to 11.8v. does this mean i have a weak alternator or bad ground or something?

 

Get the alternator tested at a parts store. If it's dropping under 12.5V with a load, it's draining the battery.

 

What kind of fan?

 

sounds like grounding issues to me.
im not sure how accurate the stock voltmeter is. i have an underdrive alt pulley, and daytime its fine but with the lights on and radio on it dips to about 12 volts at idle. if i also turn on the heater and rear defrost it dips to 11.8 at idle. off idle its almost always 13ish volts and it was more normal before the pulley swap so i think my grounds are fine. my point is its been like this for months and im still on the same battery. no problems at all with battery drain. which leads me to think the stock voltmeter isnt completely accurate.

 

i have a ground from block to chassis. should i add another ground for the battery its located in the back and ground with a 4 gauge to chassis.

 

You should be testing voltage with a DMM across the battery terminals or between the neg. terminal and the pos. lead on the alternator. A charged battery will have 12.5 to 12.8volts, and the whole idea behind the alternator is to charge it. It's not going to be charging if the load is greater than the alternator output.

I wasted a ton of time running new battery cables awhile back when I had a charging problem, and it ended up being a bad regulator in my brand new alternator. Save yourself some time and get it tested. The testers they have in parts stores will tell you more than just monitoring voltage with a DMM.