Always only 11.5 volts while running

klaucke · 04:03 PM

EDIT: new problem on same topic, please see newer post below...

My red warning light is always on, so I did a voltage test at the battery, and found:
-With the engine off and accessories off, the voltage is 12 volts exactly.
-With the engine running [fresh air fan running etc, but no lights] it is a 11.5 volts exactly.
-With the headlights on, it drops to 11.25 volts
Engine RPM has no affect at all on the needle.

Does this sound like bad alternator [or hence diodes] or a bad voltage regulator? Is there anyway to trouble shoot the voltage regulator?

pwd72s · 04-07-2004, 07:03 PM

could be either...I'm guessing alternator. But the V regulator is easier and cheaper to replace, so try that first?

ischmitz · ischmitz's Garage

It can be all of the above: Bad or worn brushes, bad regulator, 14 pin connector in the engine bay, loose wire at the alternator.

Before throwing parts at it check the easy things like bad wiring and corrosion first.

Ingo

klaucke · 04-08-2004, 09:53 AM

I checked all the connections first, ground straps, etc. Everything is top notch right now.

304065 · 04-08-2004, 11:04 AM

First, do a search here under the word "alternator."

Then search under "full-field."

klaucke · 07-24-2004, 04:03 PM

Alright, quick update:

The alternator "fixed" itself when driving around when I first got the car back together, soon after I first posted this thread. The red light would be on when the car first starting, but after a quick rev over about 3k RPM it would go out and stay out.

Then, driving one day, it turned back on, and seems to stay on always, at the same brightness. My voltage is the same as my above post:
"-With the engine off and accessories off, the voltage is 12 volts exactly.
-With the engine running [fresh air fan running etc, but no lights] it is a 11.5 volts exactly.
-With the headlights on, it drops to 11.25 volts"

I'll take a ride, and the light will go out sometimes, but after I shut the car off, and start it again, it won't go out. Also, I noticed if I *really* get get on it, and take the engine up to 5500 RPM (about), the light will go off, but then go back on when the engine drops back down in RPM. Does this sound like the voltage regulator, a bad alternator, or a loose connection? I've checked the ground straps, etc, and I can find any loose wiring, any tips? Could it be the battery (unlikely?)?

Thanks in advance!

vash · vash's Garage

do you have a battery charger to get your battery up past 12V? that would be the first thing i would do. from what i have gathered, our alts are pretty lame at bringing low voltage up, and will damage itself trying. then check all the wires behind the alt. and while you are there, take it out and take it to a reputable rebuilder, and have him/her test it. solved all my issues that way. and i got anal with all the connections. i emory board roughed them up and put a tiny bit of dieletric grease on each and every connection.

klaucke · 07-24-2004, 04:28 PM

She's on the charger now... my car sits for about a week b/w drives, and I know I have a drain due to the clock (it's noisy) so I suppose that could be problematic? However, the light popped on while driving after having driven for probably ~45 min so the battery should have been fully charged.

89911 · 07-25-2004, 04:43 AM

You can mask a charging problem for a long time by charging your battery up and making short trips. My car died while driving home from the track a few weeks ago. The battery completely discharged and I couldn't get it to turn over. My voltage was never very high when I would check it, 12-13v when running. It now measures 13.5 plus when running with a rebuilt alternator. It might be time for a new one for you.

KTL · 08:04 AM

Put your voltmeter on the system (put it pretty much anywhere) and drive around to see how the voltage changes, if at all. If no change, then your system is not charging properly. The change should be slight. Not a big amount like 2 volts. The fact that your voltage is at 11.5 V when running is not good. Like 89911 said, the system voltage should be around 13.5 - 14 V with the motor running

There's places inside the car you can connect the voltmeter so you can see what the voltage is through the system as you're driving around. Try the ignition switch underneath the dash. That's where I tapped-in my the lighting for my voltmeter and cyl. head temp. gauges. You could even put the meter on the ashtray light (if the 74 has that feature), as it's easy to get at. Just pull the light/wires out of the rubber grommet.

It's been my experience (limited) that bad VR's give you voltage spiking. A constant low voltage output would lead me to believe it's the alternator itself that's not getting the job done.

pwd72s · 07-25-2004, 08:49 AM

Good advice from Kevin...a cheap and quick way to have a portable V-meter is to buy a male cigarette lighter plug in from Radio Shack or others. You may have to beef it up a bit in order for it to stay put in the larger german receptacle...I use plastic from an old milk jug & electrical tape. Then hook a multmeter to this...set it on the passenger seat for readings as you drive.

89911 · 07-25-2004, 02:34 PM

My bell radar detector has a voltmeter built into it. Nice feature. Take that Valentine!