OK, I've been e-mailing with a member who's been very helpful but now I thought I'd throw it open for any ideas and/or help-please.
91 L-98, 6 Speed & 45ish on the clock.
The other night I was out with the top down, lights and radio only on. The battery icon pops on the display and the volt needle is down around 6/7 volts steady. I spin around and head home. About a 1/2 mile more and I see the needle slowly rise back to normal for me, 3o'clockish+. I spin again towards my destination feeling it was just a glitch and knowing full well it's never just a glitch. Another 4 miles down the road and same thing. Icon on display and 6/7 steady volts showing on gauge. I go home and pull in the garage, shut it down and refire it 2 or 3 times with nothing different. Still 6/7 volt position. I went to bed.
Sunday I searched the archives, did some research and e-mailed a member.
Monday I fired it up and presto gone-o no problem. Back to normal.
Here's what I've found so far while it's operating normal: Battery voltage is/was just under 12 volts. Good continuity in alt main wire to positive battery connection behind battery (solenoid?). Also good from that point to positive cable end, mostly. More on the mostly later. The three wire plug-in connector at the alt; all three when tested to ground showed battery voltage. Almost 12 volts as stated earlier. The alt put out 14.5 at the alt yet a little less at the battery positive terminal. With this info I stopped to think for the night-Budweiser! Wed I went to breakfast with the guys and took the Vette. Once again everything seemed normal at the onset. Made a few stops after and it reacted strangely, again. This time though the dash needle seemed to fall off slowly. It tried to recover once before falling to the 6/7 volt area. I pulled in to the garage , left the engine running and started checking voltage. The idle was erratic so by the time I settled that out and got the gauge on the alt output the dash gauge had recovered to around 10 volts and the alt was putting out 14. May have been the 14.5 but I was fumbling. I shut it down and called a form recommended guy in Sacramento. He informs me that the dash gauge is just a indication of the voltage in the battery and as we know dash gauges are not necessarily accurate. Although helpful he didn't think it was the alt and that I should look towards the battery first. Last night I pulled the batt and put it on the trickle charger and before I went in it had recovered to 12.6 volts on my gauge. This morning it's down to 12, hummm. OK, back two the positive cable. In an attempt to check continuity of the cables I noticed that if I wiggle the screw/bolt part around in it's cable case I can brake the circuit. Is this normal and if not can I somehow just replace the bolts? Any direction or ideas on what's causing the voltage drop. Would an intermittent direct short cause the dash gauge to act in the manner described? Thanks for your input. I'm going to the garage to put back the battery and it's box back in the car....Frank

 

I am no expert, but I did have problems once that were at least in part similar to yours. The culprit was a bad connection at the cable due to corrosion. I would cetainly find out why you can lose continuity by moving a cable.
Good luck.

 

The bolt in the cable.. this is the one connected at the battery?

If so yes you can replace them.. try that first.. Also how old is the battery? maybe on of the Cell's is on the way out.. if the battery is over 4 years old it is good preventive maintenance.

Also as for the Battery gauge. I belive it shows battery voltage but on my 89 when the car is running I think it is showing the actual chrage coming from the Alt since there is a direct line from the Alt. to the battery and the Alt may have a higher voltage since it is essentially charging the battery as well

Also the soleniod looking thing behind the battery is actually just a terminal junction block.

 

I think I was losing continuity because the cable nut was moving around in the disconnected cable. Sometimes touching and sometimes not. Maybe it's suppose to. Anyway I've been able to remove the old hold down bolts from the cable ends and will replace with old new ones. Do I remember something about cleaning the ends or rather how not to and what not to use/do. Something about the process affecting the circuit or ECM. Ring any bells? Frank

 

Yes Jeff, It is the one in the cable end and thanks I've got them out. The battery is about one year old per the guy I bought the car from in Sept. It's a Continental 6000. I checked it last night with the charger still attached which is why it was 12.6 and 12 this morning detached. I've got a 2nd Toyota battery that's good and did the same thing. 12.6 attached and 12 detached. Junction block works for me. Thanks, back to the garage.

 

Glad thins worked out. Every once in a while cleaning the battery cable ends with baking soda and water help keep good connections. Sounds funny, but crazy glue a penny or two to the battery casing approx. 1/2 away from the positive terminal helps keep the connections goood. The coppper draws corrosion from the battery connection.

 

Hasn't worked out yet Bob. Here's new data. Reconnected battery. Why do those headlight motors keep cycling when I attach the battery to the system?
Started car.
Alt output at alt is only 11.25
Alt output at batt pos is also 11.25
Engine off, key on, 3 wire alt plug:All 11.5
Dash volt meter after starting and running, which is usually at 3 o'clock+, is steady regaining a volt or so after starting and reads at 10 volts ish. I'm back to a bad alt. Now what do you guys think? Frank

 

If you can trickle charge your battery overnight and it is at 12 volts, then I think you can rule out the battery. Throw out the wimpy 5/16 GM batt connector bolts and buy some BIG brass batt terminal bolts (5/8 in) for a good low resistance connection to your battery! Clean the cable lugs - and + so they are bright before reconnecting them. If you can wiggle either batt cable and see a variation in voltage, then you have a broken connection from cable to lug and that cable should be replaced. Your alternator at idle with low car electrical loads should never read 11 volts or it is defective. The voltage regulator in the alternator attempts to maintain 14.3 to 14.7 volts output and when the alternator gets warm, its output will fall to 13.7 because the regulator is not perfectly temperature compensated. Buy a 10 amp battery charger and charge your battery all the way up. This will take 4 full days. Your trickle charger will take a month to fully charge your battery. Keep your voltmeter with you and if the batt light comes on and your dash voltmeter reads anything lower than 12 volts, stop with the engine running and measure the battery terminal volts and compare it with the dash. I suspect the dash voltmeter has a poor connection and has a large error. Good Luck.

 

If you're not totally baffled yet.... You could have a bad cell in the battery. Sometimes the vibration in the vettes suspension can cause one or more of the cells to break connection and can come and go with temperature position, angle of the car. Seen it happen lots in boats and 4x4s.

Just my .02 good luck and post what happened.

 

Well, so far I'm still puzzled. My new friend Richard, a alt rebuilder, out in Sacramento isn't so fast to say it's the alt. He is still leaning towards the battery like some have suggested. When I gave him the numbers he said junk the battery until he found out I was using a tiny analog sweep face gauge. I checked my other cars (3) and got varying numbers but all had low (for him) battery numbers. Alt output numbers at batt were 14vts for two and 13.5 vts at alt and batt post for the third. Batts were 12, 11.5 and 12 respectively. He didn't like the battery voltages as he thought they were too low. I'm on my way to Radio Shack to get a new digital gauge and recheck. I'll let you know...Frank