Pulsing Lights/Electrical Issue

[B-Co Kid]

1987 B-Co; 351w; Carb'd, C-6 Trans; Non-EEC from factory; 3G alternator upgrade

I've recently noticed some weird electrical issues with my rig. First, when cranking cold and the electric choke on (above idle RPMs), the battery light is flashing, approx. 1 flash/second. When I open the door, and the dome light comes on, the battery light stops flashing. When I close the door, the battery light starts back flashing. In addition, interior lights, headlights, tail lights are pulsing, just enough to be noticeable. Once the engine has warmed and at normal temp and idling, the flashing battery light goes away, but the dome lights, headlights, and tail lights still pulse. I've checked the battery, before starting, with choke on, and at normal idle, and the charging system seems to be working. I also checked with an alternator tester, and it tested 'good'. I'm not certain what could be causing these issue; any help is greatly appreciated.

 

[L\Bronco]

Hey B-CO
Sounds a lot like a voltage regulator that is on its way out.
Check the battery voltage when the lights are pulsing. If its fluctuating up and down, it is likely a failing voltage regulator or The brushes are on the verge of wearing out.
Don't rule out a bad engine to body ground connection either.
Hope that helps
Cheers

 

[B-Co Kid]

Hey B-CO
Sounds a lot like a voltage regulator that is on its way out.
Check the battery voltage when the lights are pulsing. If its fluctuating up and down, it is likely a failing voltage regulator or The brushes are on the verge of wearing out.
Don't rule out a bad engine to body ground connection either.
Hope that helps
Cheers

Thank you for the feedback L/B. I checked the voltage as you suggested; there was some minor fluctuations, but nothing out of the ordinary, and the fluctuations did not occur with the pattern of the pulsing. The ground points are good and secure. I will look to testing the voltage regulator. I did a 3G alternator upgrade from a 93 Taurus/3.8L, which has the voltage regulator attached to the back of the alt. If you, or anyone here, knows how to test that specific component, please chime in. Thanks.

 

[ShadetreeSeattle]

You have a tricky one here. I literally just posted a 2G to 3G upgrade walkthru today, so i'm keen on the electronics side of this. Immediately what comes to mind is a failing alternator, (ripple current/failing diodes internally can cause strobing of the alt lamp. but we need more info. can you pull some info from a multimeter? also...

Does the charge warning light stay on under load? you open the door and it goes away or stays illuminated? what about if you turn on other loads? like blower motor, headlights or a/c?

what does a voltage check look like under full load? is it showing less than 13.0v or does it hold steady?

What voltage are you seeing at the battery when running?

Does voltage stay steady when revving engine or does it rise in relative proportion to engine speed?

try these tests out and report back I suppose.

Thinking about it, often a high-impedance situation, on the high side or low side can cause these situations. a crummy body ground, a poor 12V connection thru the ignition switch to the field circuit of the alternator, ehh. it could be a handful of things.

 

[B-Co Kid]

Thanks for responding Shade. The warning light is only strobing when I first start the engine when the choke is on and RPMs are increased. Once the engine warms up and the RPMs drop to normal, the battery light is no longer strobing or on. With the engine warmed, and under load, again, the battery light is not strobing or on. The only issue present, after the engine drops to normal RPMs is the interior/exterior lights slightly pulsing/dimming; this particular issue occurs with the engine warmed or not. With engine cold and sitting overnight, before cranking I’m seeing 12.62V. With the engine started, and choke on/RPMs Increased, I’m seeing 14.9V, with the choke off, and engine at normal op temp/normal RPMs, I’m seeing 14.72V. The voltage is relatively steady when revving the engine.

 

[B-Co Kid]

After searching a bit more online, I came across another owner that had a similar issue, with a slightly older model than my rig. For that owner, the issue was the plug/wiring to the alternator/voltage regulator (VR). So, I unplugged and re-plugged the connector to the VR, which is mounted to the backside of the alternator, started the engine, and the issue was gone. In hindsight, I should have started the engine first, and then push the plug in more firmly, that way I would have known for certain it was the plug/wiring to the VR. In any case, the issue is resolved for now, will report any further issues. Thanks to everyone’s input.

 

[L\Bronco]

After searching a bit more online, I came across another owner that had a similar issue, with a slightly older model than my rig. For that owner, the issue was the plug/wiring to the alternator/voltage regulator (VR). So, I unplugged and re-plugged the connector to the VR, which is mounted to the backside of the alternator, started the engine, and the issue was gone. In hindsight, I should have started the engine first, and then push the plug in more firmly, that way I would have known for certain it was the plug/wiring to the VR. In any case, the issue is resolved for now, will report any further issues. Thanks to everyone’s input.

Glad you got it handled, sorry I didn’t get back to you, head down tail up up here getting ready for winter, plus Im prepping for the march meet in Bakersfield next weekend.
Cheers