Calling all electrical gurus........., my alternator saga continues Options

[East coaster]

I had a strange electrical problem with my 914 and I thought I had it resolved, but now I'm wondering.

A while back, I was driving to work and the car died. I found that the battery was dead. I removed the battery, charged it, and made it to work/home. I assumed my alternator was bad, so I ordered a new alt (alt/reg) and replaced it. I'm running 911 gauges and don't have a volt meter/amp gauge and the idiot light was not working, so I really had no indication while driving other than my stereo would crap out due to low voltage a few minutes before the engine would be affected. This gave a little warning that something was awry.

Once the alt was replaced, things seemed good for about a month or so and then it happened again. I inspected every ground and found nothing. I restricted my driving to my local hood until I figured this out and I finally thought I had.

I fired it up for a drive a few weeks back and it cranked over rapdily and started right up (as it usually does). I proceeded to back out of my driveway and started heading down the street and within 3 blocks (<1/16 mile) it began to die. I reasoned that no electrical problem can take a fully charged battery down that quickly without frying something? I could arc weld with a battery and not kill it that quick! So, I thought the battery itself is the only thing that could cause this symptom.

So, I got the battery replaced under warrantee as it checked "bad" when I returned it and it's been working OK since.

Here's my dilema (after the long winded above description!), I replaced the bulb in the idiot light and now I have a new concern. When I start the car the light is off and remains off until the rpms hit 3800 or above and then it comes on and stays on until I shut the engine off and restart. once restarted, it stays off until I hit 3800 revs. With the light on I metered the voltage and it looks good (14.2-14.4), so it seems the alt is working fine........so what's up with the damn Alt light??????

[charliew]

I had a battery develop a short that was intermittent on a 69 camaro once and it ruined the brand new regulator I had put in trying to fix the problem. When I took the battery in for a check it started smoking the test leads. Maybe your battery messed up your voltage regulator. On the chey thats where the light was controlled from. Some systems need the light to complete the charging circuit.
Put the meter on the battery terminals before you start it. Read the voltage. Start it up and read the voltage. See what happens on the meter at 3800. My older cars didn't start charging till you rev the motor off idle a little. They used the light to bleed a little voltage to the alt. regulator to make it charge.

Charliew

[Spoke]

When you start the car and the gen light is off, what is the voltage at the battery? Is the system charging at this point?

After first starting up and gen light is off, rev to 3800 while measuring the voltage at the battery. Does the battery voltage change when the gen light comes on?

If the Gen light comes on during operation, this tells you that the alternator circuit for the gen light and voltage regulator is not producing voltage. The gen light and VR have their own set of diodes (ie, positive voltage) from the ALT. Another set of diodes charges the battery.

No voltage for the gen light/VR could be the wiring or the diodes in the ALT. You replaced the alt so diodes should be ok.

Check all wiring to be sure they are securely connected.

One test you could do is check ALT by itself by removing the VR and jumpering lugs D+ and DF together. These are on the relay board where VR connects. This simulates the VR commanding the alternator for full output. You should see the battery voltage go up over 15V. This is not a test you should run for a long time (like hours), maybe only for minutes. This test will take the VR out of the equation. Rev engine to 3800 and see if the gen light comes on. Measure battery voltage before revving and after.

The D+ and DF lugs on the relay board are the 2 side-by-side lugs on the side of the board towards the front of the car. DF is the left one (driver side) and D+ is the one on the right (pass side). D+ is the one that connects to the gen light and the ALT output.

The other lug is D- which should connect to ground. Test this connection by putting your multimeter on OHMs and measuring from D- to the chassis. You should read 0 ohms or close to it. For safety of your meter, you may want to disconnect battery NEG before checking resistance.

BTW, the gen light plays an important role in the starting up of the alternator. With the gen light burned out, it is possible that the ALT will not produce voltage.

The VR gets power from either the ALT (normal operating condition) or the gen light (starting).

The gen light provides initial power to the VR when starting. The VR in turn powers the ALT armature (spinning part). Armature magnitizes with power from VR and thus the ALT generates voltage when the armature is turning. The ALT may work even without the gen light as the armature possesses a small amount of residual magnetism even w/o power from the VR.

The characteristic of gen light staying on after first startup before revving is because the gen light is like a resistor so the VR doesn't get full 12V and thus only magnetizes the armature a little bit when the engine is started w/o revving therefore the ALT produces little voltage....Until the engine is revved, the ALT spins faster, makes more voltage which powers the VR/armature and bingo: ALT starts charging and powers the VR full voltage and gen light goes out.

[Allan]

and the idiot light was not working

Not working how? Bulb burned out? Not wired in?

The bulb is part of the circuit. If it's burned out or not tied in, the alternator won't charge the battery.

[East coaster]

Idiot light was not installed when I first put the car on the road (guess I'm the idiot!). I never knew the light was a critical part of the circuit. I still have trouble believing that a stupid a$$ bulb which could burn out at any time would be a consciously critical component of a charging system!!! Why wouldn't they use a shunt res or something??

When I wired the car I didn't have the correct bulb/housing for the alt light because I'm using 911 gauges now and the 914 light was totally different. I figured I would get the correct bulb/housing someday and when/if I had to pull the gauge panel out I would addres it then. Having learned that the bulb may be a critical part of the system, I recently pulled the panel and put the bulb in.

When I start the car, the voltage is about 12.8 and the light is off. When I rev the motor the voltage climbs to 14.2 -14.4v and the light kicks on at 3800 rpm. When the light is on I'm indicating 14+ volts and when the rpms drop the light stays on and voltage is still looking good.

[TheCabinetmaker]

Gen light takes it own special bulb. It is not the same as the rest of the dash gauges.

[effutuo101]

That is a 5W bulb correct?

[Spoke]

Why wouldn't they use a shunt res or something??

The gen light is simple and provides instant notification of ALT failure. It's a VW...think KISS.

When I wired the car I didn't have the correct bulb/housing for the alt light because I'm using 911 gauges now and the 914 light was totally different. I figured I would get the correct bulb/housing someday and when/if I had to pull the gauge panel out I would addres it then. Having learned that the bulb may be a critical part of the system, I recently pulled the panel and put the bulb in.

Has the car worked correctly since the 911 gauges were put in?

When I start the car, the voltage is about 12.8 and the light is off. When I rev the motor the voltage climbs to 14.2 -14.4v and the light kicks on at 3800 rpm. When the light is on I'm indicating 14+ volts and when the rpms drop the light stays on and voltage is still looking good.

When the gen light comes on, this indicates that something is not right with the ALT +VR. With the light on, the VR is not powered much at all and one could assume the ALT is also not working. When the light comes on at 3800, does the battery voltage drop even a little bit? This would indicate ALT not charging and the longer you run the car on battery power, the lower the battery voltage will get.

Before the gen light comes on, does battery voltage vary with engine speed? You know, like 14.2 at idle, 14.4 at 2000? If so, once the gen light comes on, does the battery voltage also show the same voltage vs RPM characteristic? Also try this experiment with the lights on. This will give heavy electric load and will hasten the dropping of battery voltage if the ALT is not functioning properly.

If you have a jumper wire, try the test with VR removed and D+ and DF shorted. Rev engine to 3800 and see if the gen light comes on. If you don't have a convenient jumper wire, you can make one with a short piece of wire and 2 crimp-on spade connectors.

[sww914]

I would buy a cheap multimeter and compare it to the gauge. gauges can be wrong.
With the key on and the car not running the alt light should be on.
If it isn't the alt won't charge.
With the car running the alt light should be off. Sometimes you need to rev the engine up to 1500 or so to get it going.
With a fully charged battery the voltage should be near 14.2 with the car running and the alt light out.
The fan shroud must be grounded to the case for the alt to work.
Somebody near you might have known good VR for you to try.

[East coaster]

Spoke, Thanks for the input. The car has been on the road for almost 2 years without the gen light being hooked up and the problem I'm having began last fall, so it worked great for over a year without it.

I've metered the voltage at idle (with the gen light on) and I have about 13.8 volts at idle with every electrical load I can impart (high beams,stereo w/subwoofer amp, flashers, wipers, fresh air blower) and the voltage climbs with the rpms. So, it appears to be working OK. I just got back from a "test drive" and I now have about 60 + miles of driving with the light on and so far no signs of reduced battery capacity.....Am I chasing a ghost???

I don't think I can do the jumper too easily as the alt is buried under the cooling housing on a 911 motor. You really can't even see the alt/reg.

**SWW914, You bring up a good point that I failed to mention, when I turn the key on the light does NOT come on. The car starts, light stays off and will not light until 3800+ rpms is hit. I could drive it all day long @3500 revs and never see the light

[sww914]

The alt energizer circuit runs through the alt light, When the key is on one side of the bulb is energized by the ignition switch and the other side is grounded through the not turning alt. Once the car is running the alt is energized and there is + on both sides of the light and the light goes out.
key>bulb>alt DF. If the light comes on at higher RPM's but not with the engine stopped it sounds like maybe a bad diode in the alt, but I can't remember right now.

[sww914]

Here's a good article on 914 charging systems, it might help.
http://www.pelicanparts.com/914/914qa/914Q..._alternator.htm

[markb]

Gen light takes it own special bulb. It is not the same as the rest of the dash gauges.

I never knew this. What's different, and can you supply the specs?

[TheCabinetmaker]

Well, not sure of the specifics of the bulb itself, but I do know they are different.

Bulb on right is standard bulb for all instruments. Bulb on left is alt bulb. It's marked as "osram 12/1.2" On the far left is the holder for the alt bulb.

[Spoke]

I don't think I can do the jumper too easily as the alt is buried under the cooling housing on a 911 motor. You really can't even see the alt/reg.

**SWW914, You bring up a good point that I failed to mention, when I turn the key on the light does NOT come on. The car starts, light stays off and will not light until 3800+ rpms is hit. I could drive it all day long @3500 revs and never see the light

You can use the jumper by removing the VR. The VR is mounted on the relay board and once removed, the 3 lugs from the ALT will be visible and easily accessible. You'll need to remove the VR to check wiring to your gen light.

If the gen light does not come on when you first turn the key, then it sounds like you have some wiring issue. The gen light must come on when key is turned else there is an issue with it's connection in the ALT circuit. This may be your problem.

You can check the bulb wiring by removing the bulb and the VR. On the bulb socket, one side is +12 through the ignition switch and a fuse to the battery. Turn the key to on (you may want to disconnect the +12 to the coil as you could fry Pertronix or damage points etc. if key is left on with engine not running). One side of the gen light should be 12V. This voltage should switch on and off with the ignition key.

The other contact of the gen socket goes to D+. D+ is accessible when the VR is removed. D+ is the lug towards the front of the car and on the right side. Measure resistance from this lug to the gen socket. Should be 0 ohms.

Someone also mentioned checking resistance from ALT case to engine case and chassis. These measurements must also be 0 ohms.

If you don't have a multimeter, buy one. You'll need it again and again with these cars. Trying to debug an electrical problem like this w/o a meter is like trying to time your engine w/o a timing light.

[Cap'n Krusty]

Gen light takes it own special bulb. It is not the same as the rest of the dash gauges.

Well, that's a crock. The 911 takes the SAME instrument bulbs as the 914 (given cars of the same era), and the alternator/generator bulb is the SAME as all the other dash light bulbs (with the exception of the little bulb for the heater slide control unit). It's 2 watts. The alternator exciter circuit doesn't work without the bulb, unless someone's kludged up a low amp substitute.

The Cap'n

[TheCabinetmaker]

Then why are they different? Enlighten me oh crusty one.

[East coaster]

You can use the jumper by removing the VR. The VR is mounted on the relay board and once removed, the 3 lugs from the ALT will be visible and easily accessible. You'll need to remove the VR to check wiring to your gen light.

This is a 914-6 conversion with a 1992 3.6 Carerra engine and does not have a relay board. The regulator is built into the alternator.

I'm wondering if the regulator is bad in such a way that the gen light is working eroneously, but the alternator is charging correctly. If not, then I don't understand why the battery measures 14.4v when the light is on and less when the light is off?? I am using a digital multi-meter for the voltage measurements.