Voltage Fluctuation???
Thread Starter
Melting Slicks
Joined: Jul 2010
Posts: 2,762
Likes: 820
From: SUFFIELD CT USA 2023 C8 CORVETTE UN-MODIFIED FINALIST
2023 C8 of the Year Finalist - Unmodified
Voltage Fluctuation???
This morning about 1 mile short of work I stop for a red light in my '77 4 speed and my Generator warning lite starts flickering. It will do this if my idle is too low but I noticed my voltage gauge was swinging between 13 and 10 volts, this is definitely not normal. The light changed and I drove about a half mile with the voltage needle swinging and then everything went normal.
When I got to work I checked the belt and wiring on the back of the alternator and all was normal, no smoke, smell or anything. At a coffee brake I idled the car for 15 minutes and there were no unusual things going on under the hood or on the panel.
After work I drove the vette about 4 miles to the airport hanger where it lives and 2 of my friends ( both pro mechanics ) checked all the wires and tapped and shook everything while I watched the gauges and I could not repeat the issue. I took 2 more short test drives, again nothing!
Has this happened to anyone else???
Vette has 106,000 miles, 3 year old battery cranks strong, alternator is 5 + years old mileage on it unknown!
When I got to work I checked the belt and wiring on the back of the alternator and all was normal, no smoke, smell or anything. At a coffee brake I idled the car for 15 minutes and there were no unusual things going on under the hood or on the panel.
After work I drove the vette about 4 miles to the airport hanger where it lives and 2 of my friends ( both pro mechanics ) checked all the wires and tapped and shook everything while I watched the gauges and I could not repeat the issue. I took 2 more short test drives, again nothing!
Has this happened to anyone else???
Vette has 106,000 miles, 3 year old battery cranks strong, alternator is 5 + years old mileage on it unknown!
Last edited by BPHORSEGUY; Sep 13, 2014 at 05:31 PM.
Thread Starter
Melting Slicks
Joined: Jul 2010
Posts: 2,762
Likes: 820
From: SUFFIELD CT USA 2023 C8 CORVETTE UN-MODIFIED FINALIST
2023 C8 of the Year Finalist - Unmodified
I just don't want to replace the alternator and then find out that wasn't it. I can't get it to fail again!
Race Director
Joined: Apr 2007
Posts: 11,150
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From: South Western Ontario
The main lead from the alternator passes through the firewall plug to the solenoid. I'd check that wire to ensure it's got good connections. I believe this wire passes into the cockpit where it is spliced to a number of wires to power things and then passes out on another pin going to the solenoid. The firewall plug connections on this wire give issues since it's always passing higher currents.
Terminal 2 on the alternator plug is the remote voltage sensing and provides voltage to the regulator. Also check that the terminals on that wire are in good shape. I believe it passes through the firewall plugs by just looping in and back out.. Then, it goes to the solenoid probably with a fusible link. An intermittent on that wire could cause the issue you were seeing.
Terminal 1 with the light connected is just used to get the alternator working. Once it's producing power the light could be disconnected without affecting it. So, this isn't likely to be the problem.
Terminal 2 on the alternator plug is the remote voltage sensing and provides voltage to the regulator. Also check that the terminals on that wire are in good shape. I believe it passes through the firewall plugs by just looping in and back out.. Then, it goes to the solenoid probably with a fusible link. An intermittent on that wire could cause the issue you were seeing.
Terminal 1 with the light connected is just used to get the alternator working. Once it's producing power the light could be disconnected without affecting it. So, this isn't likely to be the problem.
Last edited by lionelhutz; Sep 15, 2014 at 11:01 AM.
Thread Starter
Melting Slicks
Joined: Jul 2010
Posts: 2,762
Likes: 820
From: SUFFIELD CT USA 2023 C8 CORVETTE UN-MODIFIED FINALIST
2023 C8 of the Year Finalist - Unmodified
The main lead from the alternator passes through the firewall plug to the solenoid. I'd check that wire to ensure it's got good connections. I believe this wire passes into the cockpit where it is spliced to a number of wires to power things and then passes out on another pin going to the solenoid. The firewall plug connections on this wire give issues since it's always passing higher currents.
Terminal 2 on the alternator plug is the remote voltage sensing and provides voltage to the regulator. Also check that the terminals on that wire are in good shape. I believe it passes through the firewall plugs by just looping in and back out.. Then, it goes to the solenoid probably with a fusible link. An intermittent on that wire could cause the issue you were seeing.
Terminal 1 with the light connected is just used to get the alternator working. Once it's producing power the light could be disconnected without affecting it. So, this isn't likely to be the problem.
Terminal 2 on the alternator plug is the remote voltage sensing and provides voltage to the regulator. Also check that the terminals on that wire are in good shape. I believe it passes through the firewall plugs by just looping in and back out.. Then, it goes to the solenoid probably with a fusible link. An intermittent on that wire could cause the issue you were seeing.
Terminal 1 with the light connected is just used to get the alternator working. Once it's producing power the light could be disconnected without affecting it. So, this isn't likely to be the problem.
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Thread Starter
Melting Slicks
Joined: Jul 2010
Posts: 2,762
Likes: 820
From: SUFFIELD CT USA 2023 C8 CORVETTE UN-MODIFIED FINALIST
2023 C8 of the Year Finalist - Unmodified
All my test runs were run during the day in warm weather. I just remembered as I was parking the car tonite that I had the heater blower on full because the top was off and the radio and all lights were on. Under these conditions I believe the alternator was barely keeping up with the load or perhaps not keeping up, when I stopped for the light I may have been discharging or discharging for the previous 20 minutes!