claydwilli

It's a bit of a long story, but hopefully someone can help me out.

I have a 1980 Vette. The other day while driving on the highway, we noticed that the battery volt meter was up in the red, followed by a burning smell, then the car died. Just pooped out and coasted to the shoulder. After a costly tow and mechanic visit, we were told by our mechanic he fixed the ‘fried wires and blown fuses, fixed the battery (which had blown it’s top off and leaked a little water), and charged it back up.’ The Vette seemed to run fine on the drive home (other than the dead stereo/radio, which was working before this occurred) but when we went to drive it the next time the battery was dead! We re-charged the battery and the process of driving fine and then dying after it was turned off repeated itself. (Oh, and we have a kill switch installed on the battery, so battery is “killed” when car is parked – shouldn’t be a secret ongoing drain anywhere.) So I got a volt meter and checked the battery and the alternator. Found the alternator only read what power the battery had (e.g. ~12), and nothing more. So we figured we had a bad alternator, bought a new one, and installed it. Thinking all our troubles are over we started her up. I checked the alternator and now it’s putting out over 15 volts; the battery gauge is back in the red; and from what I can tell the instrument gauges (MPH and RPM) are all totally dead!

Now when I picked up the new alternator I verified it as the same as the one I was swapping with them, and I installed it correctly (not really that many wires involved there), but either I have done something wrong, or there is something far more sinister afoot. Could it be the alternator regulator --- is that internal in the alternator or separate?

Does anyone have any ideas on this? I hate to just take it back to the mechanic to give him more of my hard earned money, but as it is, I don’t feel safe driving it and am getting more frustrated at every turn -- keep thinking the problem is fixed, only to run into a new one. I read on forum the other day owning one of these can be like a marriage – you love it and hate it at the same time. For me these days, how true that is.

Gordonm

Where to start on this. No pun intended. First I would fire the mechanic and don't go back. He obviously has no idea what he is doing. There could be multiple problems now from fried wiring to a obviously bad battery. A battery tha thas had its top blown off cannot be repaired by a "mechanic". I have seen a couple of them blown up like this and they are toast. The wiring harness will have to be inspected and maybe replaced with the correct wires and fuseable links. Who knows what else got fried in the process. Nothing that can't be fixed with time and money but get someone who knows wha tthey are doing first.

7T1vette

My "guess" is that the 'feedback' wire (going from battery voltage line back to the alternator via the 2-connector plug) has a break in it somewhere so that the alternator 'thinks' it needs to pump up the voltage. You can check this out by pulling that connector off the alternator, then starting the car and checking the voltage between the terminal at the 'red' wire and ground. If it fluctuates or reads low (or no) voltage, that wire is broken; it should read whatever the battery voltage is at the time. A low voltage signal on that line would cause the alternator to crank out max voltage....which would eventually fry your battery, etc.

If your voltage measurement does read the same as battery voltage, there is a different electrical problem buried in your wiring and/or grounding connections.

claydwilli

Thanks you guys, I'll take another crack at it this weekend and see what I can find out.

claydwilli

Thanks again for the help.

Here's what I did this weekend. I checked all the fuses, and found one to be blown (it was the Instrument lights, tail lights, etc).

I tested the feedback wire and it's testing good.

I also spent some more time testing the alternator and it seems to be putting out a steady 15 volts.

So, my question is... Am I crazy, and everything is fine? Was it just a strange accident that the gauges died at the same time? Should an Alternator be putting out less than 15, or is 15 safe?

Basically, I'm worried that something else will get fried, but I think maybe I'm just freaking myself out..

Thanks again for your input.

7T1vette

15 volts output is near the maximum capability of the alternator. With the battery fully charged, the alt. output voltage should be around 13.4 vdc. If the alternator keeps charging at that [15 vdc] rate, it will eventually damage the battery or burn out the alternator. Unless the battery was fairly well drained when you did your testing, the alternator [or wiring to it] still has a problem.

claydwilli

Hm, Ok.

The Battery was showing 12.5 when I first tested it. Is it possible that the battery was damaged when it popped it's top, and that's why the alternator is putting out 15? Would it be wise to replace the battery before I dive into the rest of the wiring?

Thanks again!

claydwilli

Hey everyone, I'm back again...

So I replaced the battery to test and see if that's what the was causing the high output from the alternator. Hooked it up and the vette started up no problem, and the Alternator is putting out a steady 14 volts.

I'm wondering if this is normal for this car... I didn't do any testing to see what the alternator was putting out when everything was working so I don't have a baseline.

So far the issues that have come up are the Radio is dead (I think it might have been fried when the car originally had it's trouble (see first post)), and the instrument panel is dead (RPMs stay all the way over past 7.0 and the MPH are all the way under 0). The other gauges are fine, the lights all work, etc.

Right now we don't even drive it because I don't want to cause more trouble, and my wife gets depressed any time she goes into the garage... It's her baby after all.

The car is a 1980 with power windows, locks and rear defrost. Does anyone know what a good baseline voltage reading from the alternator might be?

Thanks again!

mrvette

Yes, with a fresh new fully charged battery, you alt should put out not over 14 volts when first started...ok I can go 14.8 if you cranked a few seconds....say 15 seconds of actual starter time....

but that should relax in a few seconds to 14.x and stay there for a little while, then relax further down to 13.4 or so after say ten minits running....

sounds like you are good to go, dunno about that old battery and the batty mechanic.....

Project80

claydwilli,

Sounds like you still have concerns over the charging voltage. The charging system should put out at minimum of 1 volt over battery voltage (12.6v). Your charging range is from approximately 13.6 volts up to 15.5 volts. Higher than 15.5 volts is going create problems. The regulator will change the charging rate voltage according to the battery voltage. Without computers to supply voltage for, the 1980 system is ok at around 13.5 to 14 volts if the battery was fully charged. Did you use a digital or analog meter to check the voltage?

claydwilli

It's an analog. I thought about that after I posted, thinking maybe It's just a little hard to read. If acceptable readings are up to 14, then it sounds like I'm doing ok. I might be stressing over nothing (and that's a good thing!).

Project80

Unless the analog meter is "mirrored" to help with the accuracy of the reading, it could be slightly off as you look at it. Craftsman (Sears) sells an OK digital meter for about $20.00 (wait until it's on sale). I prefer the digital when it comes to checking the charging system.
Even with the analog, check it a couple more times to make sure your in the target voltage.

http://www.craftsman.com/shc/s/p_101...lectrical+Shop

claydwilli

Thanks Project80 (and everyone). There is a Sears just down the road from me, so I'll check that out and see if I can pick up a more accurate meter. I checked it again yesterday and it's looking like it's still right around 14. I didn't drive the car or let it idle for too long, and it always takes about 10-20 sec to crank up the first time, so I'm thinking mrvette is right about that.

oh, and also the RPM gauge randomly works now.....Not to sure what that's all about (shrug) but who am I to look a gift horse in the mouth.... MPH gauge is unknown right now as I didn't drive it, but plan on taking her out and around the block this weekend to see how she does.