Lights dim/radio dies

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Belvedere66

Belvedere66

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I am almost embarrassed to have two threads with different issues but here goes....last night while coming to a stop my lights dimmed almost to nothing and my radio cut out. After a second it all comes back to normal. I chirped the accelerator a few times to see if it would do it consistently and sure enough once the RPMs dipped after taking my foot off the pedal, lights almost die and radio cut out. The last time I did it my radio/turn signal/backup lights fuse blew. Could this be a bad regulator?
 
I guess it could be but it more sounds like a weak supply of power from the battery to your accessories.
The battery should power those things just fine when the alternator isn't running fast enough to do it.
 
Hm that is a good point, never thought of the battery. It's weird thought it would blow a fuse due to not enough juice. Figured that's only for too much lol
 
^^I would lean towards this as well. If your alternator is "dropping out" at low idle, there still should be plenty of battery voltage. Start by reading the infamous MAD article, and make some voltage tests

MadElectrical.com - Electrical Tech

This one on ammeters

Catalog

There's a simplified diagram in the article which illustrates primary power distribution in these cars, and points up a few places they fail

amp-ga18.jpg


Follow along:

The FIRST big place of voltage drop problems is the bulkhead connector. Notice that power comes off the battery, through the fuse link (RED) and through the bulkhead connector

Next for problems is the ammeter, the terminals themselves as well as the ammeter internally

Next down the line, in the BLACK ammeter lead is the WELDED SPLICE. This is RARE but it has happened. Notice that splice branches off to headlights, the ignition switch feed (also for accessories!!) and the "hot" buss to the fuse panel (brake lights, etch). If that splice comes apart, you will have drop problems.

Next is in the fuse panel, poor connections at fuses, etc.

Only way to FIND this is to get a multimeter, and make voltage tests. Compare "what you have" down the line, at the various points............to battery voltage.

Also, in this particular case, the drop from the alternator output stud, from there to and through the bulkhead (BLACK) and back to the ammeter can be a factor.
 
Did a simple test just to see output. While idling alternator output was 15.2 and battery was at 14.6. While not running battery sits at 12.5 which is normal. Sound ok so far?
 
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Also checked some voltage drop locations. Gets pretty consistent numbers all the way to the fuse box. That little 20a fuse for the radio is blowing as soon as I start the car now. The voltage jumps on startup and eventually settles but will spike occasionally under heavy load. 14.9volts to the fuse box seems high
 
Belvedere66 said:
Did a simple test just to see output. While idling alternator output was 15.2 and battery was at 14.6. While not running battery sits at 12.5 which is normal. Sound ok so far?
Click to expand...
Should not be that far apart in voltage when running, sounds like bulhead connector has high resistance.
 
It is. This may or may not but MAY be related to the problem

Here's the deal, "original wiring"

"The path" from the battery all the way to the voltage regulator (including the ground path) MUST be as close to battery voltage as you can make it.

On the plus side, the path is battery.....fuse link.....bulkhead connector......ammeter connections,......through the ammeter...........to the welded splice.....(in the black ammeter wire)......and branches off to ignition switch, fuse panel and headlights, a couple of other things "some years............"

Then continuing at the ignition switch connector.........through the switch.......back out the switch connector,......and out the bulkhead on the dark blue "run" wire (IGN1).......and to the VR ign terminal

Each one of those points is a potential for and probably IS a voltage drop. If it's bad enough, voltage can sag sometimes.

HOW TO CHECK....

You have a two edged sword, here, I would shoot one problem FIRST and then check the OTHER

So start with the VR and you MIGHT fix both problems.

With the key in "run" but with engine stopped, measure between VR "ign" terminal and battery PLUS. This produces a VERY low voltage, the lower the better. More than about .3V (3/10 of one volt) means you need to attend to it. Each bit of voltage in that measurement ADDS to the charging voltage. That is, if the regulator is at "set at" 14, and the measurement just describes produces 1.5V drop, then the battery will RUN at 14+ 1.5, that is 15.5V
 
If you fix the VR and you still have problems, attack them again. Check the fuse panel busses (there are two, one "hot" and the other fed from "accessory" and if THEY show a difference to the battery, then trace that path back. ANYTHING you check MUST be loaded. EXAMPLE. If you are looking for drop in the accessory section of the fuse panel, turn on "stuff" like the heater, radio, whatever you can 'get' to come on to load the system.
 
Well now that fuse is blowing when I turn the key to run. I can watch the filament bend. Then once they is turned to start, boom, fuse dead. Something has to be grounding out or something.
 
Does fuse blow in accessory position, does ammeter go 'way into discharge as fuse blows? Old regulators get stuck contacts but should be "trying" to keep meter centered if battery is already fully charged.
Read the FSM section on mechanical regulator adjustment, but it certainly does sound like something is drawing too much current, creating a voltage drop at points of high resistance.
 
Belvedere66 said:
That little 20a fuse for the radio is blowing as soon as I start the car now.
Click to expand...

That will be a separate problem (like a short under the dash in the radio or cig lighter wire.)
A bad lighter insert can do this, as a can anything inside the socket that does not belong in there (like a penny) :D
Might want to just leave that fuse out until you find the problem there and continue trouble shooting the other stuff first.
I am assuming the main problem still exists after the fuse blows, right?
 
Mildly irrelevant note: Only thing in my 66 Belvedere that bypasses the ammeter is the conv top switch. If the top is operated with the engine off, the ammeter does not respond. If the engine is running, the hydraulic motor load causes the ammeter to go halfway into the "charge" zone, because the load causes the voltage to drop, and the regulator responds, but it's "fooled" by connection to the input side of the ammeter.
This serms to have been the factory configuration, there is a dedicated wire for the top motor with a ring terminal, it was that way when I got the car in 1977, and I didn't find anything else to suggest it had been fooled with.



Posted from my 1966 Plymouth Belvedere II convertible.
 
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