Here are the symptoms with engine idling or off.
Stock headlights go out where high beams are turned on.
Brake lights don’t work.
Turn signals stop working when any additional electrical load is introduced.
New battery as 2018 battery dropped to 5 volts when attempting to start. Battery tender functions.
Stock alternator. Maybe original 1971.
Car is in San Diego and I’m in Sacramento. Will be going to SD after New Year.
Intend to do the following diagnostics.
Check alternator function. Check for voltage drop when accessories are activated. Check Headlight and taillights grounds.
If alternator is defective, any thoughts on replacement of alternator with a 3G Ford or Delco 10/12 ci?
Any suggestions for further diagnostic tests?
The factory wiring is good to 42 Amps. The replacement alternators put out way more than that. So complete wiring harness replacement is needed if you go that route.
The brake lamp is unrelated to the headlamps. Likely you have more than one problem.
Thanks Royce. I know I need to check brake light circuit from fuse to lights, Correct me if I’m wrong, wire sizes and condition are designed for demand, not for supply i.e. if the regulator is functional , excess voltage is not pumped into the wire harness
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Well there is a problem with your thinking. The factory regulator is simply an on / off switch that connects the alternator when the voltage is below a certain point. Amperage is uncontrolled. Smoke will emit from the wiring. Then it will not be any good any more.
Royce I think you have to be more specific. The charge lead from the alternator may be undersized resulting in heat when you try to run a modern alternator and it is trying to dump a bunch of current into your low impedance battery. This requires you to upsize one wire from the alternator to the battery side of the solenoid. All other circuits are fuse or circuit breaker protected in some way and the amount of current they pull is a function of the resistance in the circuit. The battery in your car has incredibly immense current capability far exceeding the alternator. So having a bigger alternator is not going to compare the the current potential you already have.
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I appreciate the information. If I up grade my alternator, I will certainty upgrade the wire to the battery. If I use a 3G alternator, likely, it will be necessary to rework the alternator wire harness.
Back to the original post. Voltage dropping to 5V while cranking indicates excessive current draw to the starter, most likely bad connections, corroded connections, or wiring that is no longer up to snuff.
The other functions you mention indicate that the car is running on the battery and not the alternator, so you need to examine the voltage regulator and alternator and associated wiring closely. Most auto stores will check the alternator and battery to see if they are good or not.
Midlife, after installing new battery, car starts as it should. We are on the same page as far as testing the alternator and regulator. This car sat for 5 years before I bought it in August. I need to get the electric charging system in order before I start trouble shooting the light issues.
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To save trouble and extra trips, have any alternator you plan to purchase tested before you leave the store with it. Same goes for starters.
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It sounds like we are troubleshooting multiple issues here…
If they are newer halogen lamps then you may be tripping the relay in the headlight switch. Normally this takes a few minutes and the lights will cycle off, then come back on when the relay cools, but if the switch is old / worn out then it may show different symptoms.
This could be related to a bad turn signal switch. Or may be two seperate issues.
Six year old battery. Dropping to 5V is a good indicator that the battery has reached the end of its useful lifetime, IMO.
As for checking alternator function, that’s fairly easy. Start the car and check the voltage at the battery. You should see about 14.5V between the battery posts with the car running. If so, your alternator and voltage regulator are most likely good (there IS a possibility of a good output with a bad diode in the alternator, but that’s not very common).
If I’m way off-base then I’m sure someone here will correct me 
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Thanks for your input.
The headlight switch contains a circuit breaker, not a relay.
The best thing to do for the lighting system, regardless of headlight type, is to install a relay harness in the headlight circuit.
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Is it actually a circuit breaker, or is it a bi-metallic relay? I’ve never disassembled one, but it seems to me it behaves more like a bi-metallic relay.
Relay uses an electromagnetic coil to open and close contacts to operate other circuits. Headlight switch contains a bimetal switch that functions as a circuit breaker to open the contacts when it gets hot due to overcurrent.
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I have always seen and heard it described as a circuit breaker.
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Relays generally will not reset them selves. This circut breaker will reset when the excessive load goes away
sfhess That is the plan after I install a set of H4 lights.
All this discussion about tripping the headlight switch circuit breaker, makes me think that some of you believe my headlights going out, when high beams switched on, is due to excessive draw, My cougar has stock (very old ) lights.
The original headlights shouldn’t draw more power as they age, so if the breaker is opening, it would more likely be due to an intermittent short somewhere in the wiring to the lights, or a weak breaker.
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Yes, that is one type of relay. There are also thermal relays that use a bimetalic strip to open and close contacts, like a switch, and are self-resetting.
Relays can be self-resetting just like a circuit breaker.
Circuit breakers protect against overcurrent conditions.
Bimetallic Relays protect against high current draw that causes overheating of components, like wiring.