Charging/Voltage Question

stevedee · stevedee's Garage

After getting my 74 2.0 started (finally!), I noticed that the voltmeter on the dash sits a little bit above 12V while driving during the day with no lights on, and a little above 10V while driving at night with the lights on. Day or night, using the turn signals or the brakes causes the voltmeter to drop another 2V from previous levels.

Is this normal? I say no. The PO said the car had had a charging problem, where the battery would go too low to start the car after about a week, and they thought it was the voltage regulator. They gave me a new VR when I bought the car as they had not had time to install it. I think it might be the alternator or a bad ground somewhere.

Anybody seen this, or is it normal operation?

Thanks.

SD

lapuwali · 04-02-2004, 05:09 AM

This isn't normal. It should read 13-14v while running, 12v engine off/key on, and 9-10v only while cranking. However, the first thing to check is the voltmeter and associated wiring itself. Try connecting a voltmeter directly to the battery terminals. If you're still getting low readings, then it could be any number of things. Bad engine ground, bad alternator connections, or even just a duff battery. If the charging (G) light on the dash is going out, it's probably not the alternator itself. It *may* be the regulator, but I'd check the other items first.

jamcleod · jamcleod's Garage

it may be that the factory gauges and their indications are not the most accurate... put a VOM across the battery terminals when the engine is running and measure the V. you can see the voltage fluctuations when the turn signal is on, lights are on....

stevedee · stevedee's Garage

Thanks. That's good info. Took a good Fluke DVM home from work today. I'm probably going straight to Hell for doing it. Looks like I need to buy some better test equipment. These little Radio Shack gizmos I have ain't gonna cut it any more.

SD

lapuwali · 04-02-2004, 07:15 PM

Oh, I suspect the Radio Shack DVM is plenty accurate (hope so, I can't afford Fluke stuff). It's the in-dash voltmeter (esp. the gauge that came with the center console) that's likely way off. It's not known to be all that accurate. Plus, connectors age and corrode, so who knows how much voltage drop you're reading just from that.

Connecting a DVM (any DVM) directly to the battery should remove any doubt about the health of the charging system. If there is a problem, you still won't know if it's the alternator, the battery, or the wiring between them, but you can sort that out step by step.

If you do discover the in-dash voltmeter is reading low, start cleaning connections, and consider buying an aftermarket VDO, which will probably read more accurately.

914GT · 04-03-2004, 06:56 AM

You can pick up a good digital multimeter at Harbor Freight for $12.95. I bought a waterproof digital dwell-tach-VOM at Autozone a few years ago that was inexpensive and have had no trouble with it.

I remember I used to 'borrow' stuff from work all the time, then forget to take it back. Now with $$ tight they don't want to buy new equipment any more so I find myself having to take back to work the stuff I borrowed over the years.

pbanders · pbanders's Garage

For checking battery voltage, IMO, the cheapest Radio Shack analog meter is as good or better than any of the high $$ DMM's I own. I'd rather have an analog movement when watching the cranking, helps you spot any weird stuff a lot easier.