Question:
Well my reliable 1997 T-600 has been since I purchased car 9 months ago dropping from 13.75 volts to 12 .1 volts when I put lights on.The car does not hahe an amp meter. I never had any starting problems or any lights dimming. Last week the volts dropped to abouy or below 10. the dash lights dimmed with all running lights, didn't
seem to effect headlights. I turned off lights for a minute and when I turned lights back on voltage was back to normal for about 10 minutes,
then problem started all over again. I removed alternater and had it tested. It was fluctuacting
so I replaced alternater. I also disconected all 3 batteries and had checked all checked good. I also cleaned all battery connections. The voltage
still stays at about 12.1 and 12.2 with lights on.
I will see a voltage drop when I turn on a/c blower moter also, down to about 13.25 volts. With all oter accesseries off I can turn on my 600 watt inverter connected straight to batteries
with small refridge. and tv on and not see a drop.
I was told Icould have a bad ground. I was going to try a good pair uf jumping cables to alternater ground as well as to battery ground. Some say that between 12 & 13 volts is normal with all lights on.I welcome any advice
thanks Ronnie

Answer:

Hi Ronnie,
Tilt your steering wheel back, unscrew the main dash panel and swing it out of the way. Stand on the step and look past all the wires to the firewall. There is a ground stud back there, and the nut is either loose, or has fallen off. It's metric, so if it's off, you'll have to scrounge one up! If you have a hard time finding it, look on the engine side, up high, below the wiper motor, you'll see the other end of it.
Ian
When you turn over enough rocks, you cease to be surprised at what runs out.

Answer:

You didn't say what kind of engine you have but on my Cummins that I just got rid of, the alternator ground was on the left side of the motor. I had it come loose one day and caused the same problem, plus burned up my alternator. You might want to check that out.
car safe.
The proper following distance for a car is one car length for every ten miles per hour. Please do not compromise my following distance by cutting in too close when passing me. Wait for the lights.

Answer:

Thanks Ian & Guardrail, I tried to ground alternator & battery to chassis and had no results. I will look behind the dash for loose ground. I will post results.

Answer:

Dash Dimmer switch may be problem, also did you check the resistors in the battery boxes- 50amp and 135 amp (black). once corrision starts it can travel the length of wire. May also be a battery cable that you can't see. We solved that problem when we ordered last Kw's. All those resistors and solenoids goes on the firewall. Problem solved!!!

Answer:

the Voltage Regulator.
I had one 1 time that was not working proper.
Sunnrunner,makin money

Answer:

Redwing you are right about the dash dimmer switch. I accidently stumbled on the dimmer switch when dusting dash off. I turned dash lights off and had all lights on during daylite
and notice I had 13.5 volts.I played with switch and volts dropped ! Thanks everone for the help.