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??????

[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

[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.