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Discussion Starter · #1 ·
Just purchased a 65 fastback but the entire electrical system pulses when the lights are turned on. Took a chance and replaced the voltage regulator (no help) and took the alternator off and had it checked. Works like a new one. Does anybody have any ideas on what to check next. There's nothing else taxing the otherwise healthy 289.
 
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Discussion Starter · #3 ·
No. That's the only time I SEE the problem. I'm sure it's occuring all the time. Your idea is worth a shot checking though. I'll stick a voltmeter on it tomorrow and check it out
 

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Leave the headlights on for a while, then check to see if the headlight switch is hot. Be careful. I will be real hot. Had the same problem with my '70. Had a broken wire at the headlight switch...
 

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Does your car have halogen headlights? If so, the switch won't
handle the additonal amp draw & neither will the wiring. You might
also check for a loose ground wire for the lights.
 
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Discussion Starter · #6 ·
If all other ideas pan out negative, check the ground (screws tight?) for the Volt reg or the connection in the plug from wiring harness to the Volt reg. I found pulsing in mine came from poor connection with the plug into the Volt reg.

Shop suggested a new harness and made noises about how long it would take. I took it home, fiddled around, and all better. May or may not be your issue, but a free check to see. Good luck.
 
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Discussion Starter · #7 ·
My 65 coupe does the same (when it's idling), my neighbor has a 65 fastback and it does the same too.

When parked with the engine at idle and you open a door you can see the courtsy lights pulse; if you rev the engine up a little the pulse goes away.
 

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This is a copy of a reply I sent yesterday to a VMFer who
had the same problem:

I had EXACTLY the same situation with my '66 vert. This pulsing is normal with a mechanical voltage regulator. One of the relays inside the regulator
is switching the alternator field winding 'on' and 'off'.
This is causing the alternator to 'generate' or 'not generate' charging voltage. The switching rate will vary based upon alternator RPM and electrical system load. I
had checked all wiring connections, grounds & belts and still had this 'problem'. I cured the problem by simply upgrading to a Motorcraft electronic voltage regulator. It has the same
mounting hole spacing and electrical connector. Electronic regulators switch the field winding so rapidly that you don't notice the pulsing. I bought it from NPD and it
was about $26.

In your situation, the pulsing becomes more noticable when the headlights are turned on (more current is flowing
through the battery). With headlights on, system voltage is lower when the alternator is 'not generating' charging voltage and the greater voltage flucuations become more visible.
Good Luck...
 

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My primary search would be:

1) Headlight switch - these animals get worn out over time. Additionally, if you do convert to Halogen lamps, the old headlight switch can fail. I have installed relays to provide the 12vdc from the battery to the headlamps, and the headlight switch controls the relays. My headlight switch will last a long, long time that way.
2) Grounds! - broken, cracked or loose grounds can cause lots of trouble! Circuits won't work if only the positive side is there. I had a problem with the turn signal indicator dimly illuminating when the headlights were one. It turned out that the ground wire for the headlight/turnsignal on one side was broken. Lots of fun troubleshooting that one. Now that I know, it is usually the first thing I check!
 
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