Voltage Drop

[diesel freak]

I replaced my alternator belt and it seems to be pretty tight. I am reading 13 volts on my Voltmeter or Amp meter but at night when I turn my headlights on the meter drops down to 11 volts and my headlights dim and the radio goes on and off. Interior lights also dim. What is going on? Could it be my voltage regulator, is the new belt too slack or is my alternator not putiing out enough. The brushes looked fine and it runs great in the day time. Would appreciate some advice. I am now afraid of the dark. By the way my ride is a 1986 Golf Diesel with air.

[TonyB]

You most likely have a poor connection somewhere. I'd measure the voltage at the alternator terminal - from the terminal to the alternator housing. That should be 13.8 - 14.2 volts or thereabouts. If that's OK, then measure from the alternator body to the car body - that value will be the voltage drop in the ground connections. Ideally should be 0, but .1-.3v is OK. Then from the alternator terminal to the battery - that will give you the voltage drop from the alternator to the battery (+). Again it should be low. Same for the battery(-) to the car body. All tests with the car running and headlights on.

You should be able to track down the connection(s) where you're losing voltage using this stategy. Ground connections are always suspect. When you find a connection with a high voltage drop, take it apart and clean it well.

TonyB
81 Dasher
81 Caddy

[tylernt]

Inspect the wires from the alternator where they attach to the battery. Most importantly -- peel back a bit of insulation to look at the metal underneath. On my car, the copper underneath was all corroded a nasty puffy white/green, I presume from battery fumes. Just to be safe, I replaced it all the way back to the alternator with new wire.

[82vdub]

You can also bring the car to most shops and they can test your system for you, if you don't have the capability to do this. Could be that the alternator has also decided to take a stroll through the weeds at the same time you did the belt.

[coke]

I would pull the brushes/regulator assembly out and see if there is any meat on them.

[Fatmobile]

Even a poorly grounded regulator can cause that.