Weird Electrical Problem? - Pontiac GTO Forum
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post #1 of 10 (permalink) Old 03-03-2019, 01:22 PM Thread Starter
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Weird Electrical Problem?

I have a 1968 GTO convertible that is basically stock; 400/4-speed. I tuned it up a while ago with new cap, rotor, points and condenser and set it to spec and it ran great. It's a fun driver but I don't take it out much in the cold weather so I start it once a week and let it warm up to operating temp, maybe drive it up and down my street. Recently the battery went dead even though it was on a trickle charger and only 3 years old, so I changed that. Then I noticed when I started it that the GEN light was on so I checked and the alternator was putting about 18 volts into the battery and while it was idling every now and then the rpm's would drop and occasionally it would stall but would start right back up. Since I thought 18 volts to the battery was too high I changed the voltage regulator. Now when I start it and let it run at idle the GEN light is off but the voltmeter gauge swings back and forth between 14 and 16 volts in a rythmic cadence, like a turn signal is on (it's not). If I get the rpms up to about 2K and hold it steady there, the voltmeter stays at a steady 14 volts. If I drop it back to idle, it will continue to swing between 14 and 16.

The few operational gray cells that I have left tell me to pull the alternator off and get it checked but before I do that I thought I would reach out to the folks in this forum for their thoughts. Thanks in advance for your help.
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post #2 of 10 (permalink) Old 03-03-2019, 01:51 PM
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I would look at the simple things first. Remove the battery cables one at a time and inspect/clean the post and the cable connector. If you are going to take the alternator down for a check up, take the battery also. This next step is a little more involved but I would remove the wiring to the starter and inspect for corrosion, clean and reinstall. On my car, the alternator charges the battery thru the connection on the starter. YMMV
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post #3 of 10 (permalink) Old 03-04-2019, 11:17 AM
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Sounds like the voltage regulator is not working properly.

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #4 of 10 (permalink) Old 03-04-2019, 08:44 PM
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Yes could be regulator, also if it pulses and RPM remain constant......could be a short somewhere, a surge.....check your flasher under the dash near parking brake, the round silver thing just bigger than your it flashing .....clicking? Disconnect it and see if there is any could have a short in the bunker circuit and it is flashing......just something easy to check...

The wiring to the regulator should be checked as Cj mentioned.....also grounds must be tight all around. Could be internal to alternator as well even if new ....but make sure all your wiring connects are tight. Dead battery cells should be considered as well, when your battery runs way down and your alternator tries to charge it, can burn up the alternator and or regulator.

Alternators are designed to “maintain” a properly charged battery. Trickle chargers should not be used as they really hurt a battery. A battery maintainer, with the ability to give a strong charge when needed or a small charge when needed is preferred.

The old cheap battery chargers can do more harm than good. You have to check if the battery is good with a load tester, either a micro load or a full load. A volt meter is not sufficient if the Battery is suspect. Garages have a VAT tester, they can test it in a minute. So definitely test both battery and Alternator.

Now if your idle RPM is surging......could be even more stuff. You will get it, stay with it.
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post #5 of 10 (permalink) Old 03-06-2019, 07:59 PM
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Voltage regulator most likely. And if you ran it for any length of time with the over-charging condition, you may have burnt your points. Check those visually. As a side note, you are doing much more harm than good by starting your car and running it for short periods of time. If you start it, you should drive it 5 to 10 miles minimum. Starting and shutting down or running around the block in cold weather causes moisture from combustion to build up in the engine oil and turn corrosive on the internals. Also a great way to rot out an exhaust system and cause excessive wear due to many cold start cycles. Better off leaving the car alone during the non-driving months. Trust me....your car will thank you for it.
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post #6 of 10 (permalink) Old 03-14-2019, 12:37 PM Thread Starter
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Update to Weird Electrical Problem

Well, I've done everything that everyone has suggested. I replaced the voltage regulator (again), pulled the flashers out, took the alternator off and had it tested (it's fine) and (one at a time) swapped out the cap, rotor, condenser and the points. Nothing changed until I swapped out the points to the old set that I took out a while ago. I adjusted the dwell and the car now starts and runs fine. So, the suggestion about burning the points (they actually look fine, though) was a good one. That seemed to solve the runabililty/stalling problem. However, I still have the weird voltage pulsation at idle. I checked the voltage to the coil with the ignition on and it's a steady 6.5 volts. At run, it is a steady 14 volts. Same at the battery. But the voltage is definitely going up and down (rhythmically) at idle because the interior lights get bright and dim in rhythm with the voltmeter.

Is it possible I have twice put in the wrong voltage regulator? I can't figure out what is causing this!
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post #7 of 10 (permalink) Old 03-14-2019, 01:08 PM
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So, if you've done all this and you're still having this voltage, it sounds to me like there's still a drain on the system coming from somewhere. If I were you I would literally unplug EVERYTHING not associated with actually starting the engine and running it. Disconnect all wire harnesses going to the headlights, tail lights, interior lights etc. You should only have your engine harness plugged in. Once you unplug all of these things hopefully there is no longer the voltage fluctuation, if there is, you know its something related to the battery, charging system or ignition system 100%. If the voltage levels out, slowly start to plug all other wire harnesses back in, or replace fuses etc. keep an eye on the voltage meter and see which device you plug in triggers the voltage to bounce again. Good luck
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post #8 of 10 (permalink) Old 03-14-2019, 04:24 PM Thread Starter
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Actually I did that by pulling all the fuses one at a time. So I definitely think it is something in the charging circuit. Thinking about this further, I remembered that both the alternator and regulator were replaced years ago. The regulator was not a Delco Remy. It looked the same, but now I'm thinking that something about it was different. I'm going to pursue that line for the moment and see where it leads. Thanks for your reply.
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post #9 of 10 (permalink) Old 03-14-2019, 07:26 PM
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Wilma - "I checked the voltage to the coil with the ignition on and it's a steady 6.5 volts. At run, it is a steady 14 volts. Same at the battery."

PJ - Big problem right there. With engine running, the voltage to the points should be about what you have when you simply turn the ignition on (no engine running), 6.5-7 volts. When you turn the ignition to "Start," that is when you should have 12 volt battery voltage only to supply the coil with a good hot "kick" to fire up the engine and when you snap the key back to "Run," the resistor wire takes over to drop the voltage down to 6.5-7 volts so the points do not burn out. 14 volts to the coil with the engine running means you have an electrical problem that is providing too much voltage.

If you, or someone else, has ever done an upgrade to electronic ignition, these typically require 12 volts to work and the resistor wire going to the coil is either removed & replaced, or a wire is re-routed to the coil drawing from a known 12volt source.

So first you want to look into the wire (s) going to the coil of which you should have 2 of them, the 12volt sourced wire when starting the engine and the resistor wire that the engine uses to run on so you do not burn your points. It sounds like the resistor wire is in place and working seeing you have 6.5 volts with the key in the "On/Run" position with the engine off. You need to figure out why 14 volts with the engine running.

Make sure that no one has wrongly wired up an additional wire from your starter to the coil. You should only have a "purple" colored wire going to the "S" terminal on the solenoid that activates the starter to spin when you hit the ignition switch to start your engine.

Next would be your ignition switch. These go bad. It is possible that something has been switched or jumped on the back side where the connector plugs in OR there is a short internally in the switch itself.

You will want a wiring diagram to trace wires and test them to isolate your wiring problem.
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post #10 of 10 (permalink) Old 03-16-2019, 08:48 PM
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If your alternator has a lifetime warranty take it and have it swapped out. They have told me mine was good in my f250 only to find out they were wrong. I asked for a replacement and sure enough, the problem was fixed. Not sure if a bad one will make your voltage go higher, but I have seen stranger things.
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