Signs of needing a new alternator?

chrisreale · 12-03-2002, 09:13 AM

When driving, with no accessories, voltage is fine. When I am idleing with lights on, the voltage drops to 11. As I drive off, it goes back to above 12. When I turn the blinker on, the volt guage ticks back and forth with the blinker. The generator light seems to always be glowing, never fully light, but never off. Are these signs of needing to replace the alternator in the near future?

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Signs of two problems.

One, you have dirty fuses. Fuse #8 (or is it #9?) provides power to the alternator light. Replace it and clean off the metal fingers that hold it. No, really.

Two, the stock voltmeter is there mostly for entertainment. Figure out where it usually reads and then only worry if it behaves differently than "usual". It will not really tell you much about the health of your charging system; at least not in absolute terms. In other words, "they all do that".

--DD

tryan · 12-03-2002, 09:51 AM

my console gauge is about 1.5 volts different that what i read at the battery.

search the posts for headlights and idle. check/clean the fuses

it's all entertainment is correct. that big round one in the middle is the best one.

John Rogers · 12-03-2002, 01:20 PM

You did not mention how old the batt is or how well it holds a charge if brought up to full voltage? I have found that the dash light will tell you which way the current is flowing in the electrical system, i.e. light off batt is getting current, light on dimmly batt is giving a little current and if bright then batt is giving a lot of current(power). I also have found with these fairly old fashioned electrical systems that when the batt starts to wear out then the alternator will start having to work more which causes more load on the voltage regulator and they generally will fail at about the same time. The easiest check is to put in a new batt and see what happens and then if the light stays on the alt and reg will need replacement. Some will say just do one, but they are pretty closely related and in the long run better to do both. Finally I found that anything except Bosh alt's don't seem to work well since the alt is used in other cars. Good luck.

bob174 · 12-03-2002, 06:39 PM

Agree with what's said about the guage. However the dimly lit alternator light gives some credence to a charging system problem. Your best bet is to put an engine analyzer onto the car that will check the condition of the charging system. They will typically allow testing of the direct output voltage of the alternator, and also allow you to verify the condition of the voltage regulator. It could just be a voltage regulator that's tired.

scg · 12-03-2002, 08:52 PM

Could be a bad diode...

A system check as described above will help find the problem.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Replacing the fuses and cleaning the "fingers" is both cheap and easy. It's a very good first step. It's probably easier than finding the time to drag the car to a shop that has an "analyzer"...

You can also use a real voltmeter to measure the voltage across the battery terminals themselves. Not the wires, not the clamps, but the posts. You should see over 12.6V with all the lights and such on, as long as you are over ~1500 RPM. Over 14.5V is not good either.

Check the "alternator troubleshooting" tech article for more info.

But I really do suggest cleaning up those fuse holders and replacing the fuses first.

--DD

tod914 · 12-05-2002, 06:35 PM

new voltage regs are cheap and easy to put in. See if that helps

bob174 · 12-05-2002, 06:37 PM

Dave, I've got an "engine analyzer" I bought from Sears in '87 when I bought my first 914. It's got all kinds of testing capability for charging systems and breaker point ignition systems. With the proliferation of computer controlled ignition and solid state charging systems, they probably don't make them any more. But it was $57 in '87.

chrisreale · 12-05-2002, 07:08 PM

Well, I changed the fuses, cleaned off the fingers (not the best cleaning job, might have to re-do it) and the light still is dim. Idleing, with everything on, I read 12.65 volts at the battery. My guage says less. My guess is its a dirty contact somewhere.

tod914 · 12-05-2002, 08:39 PM

i had dim dash lights too - it was the engine wiring harness. The part that connects under the relay box in the engine comp was loose.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

What kind of voltage do you get at 2000 RPM? If it's below 13.5V, you definitely have a charging problem.

Check this tech article, it should help you pinpoint your problem:
http://www.pelicanparts.com/techarticles/914_alternator_troubleshoot/914_alternator_troubleshoot.htm

--DD