Lights dim and then...

[jmanscharger]

We had a car show last night at the local fair. I drove my 69 Yellow Charger and noticed the interior lights dimming when I take my foot off the gas- and the radio going out. Other than that the car runs great. Two of my friends and our wives and kids took out three Chargers total. Afterwards I let one of my friends drive the yellowcharger and the car totally dies on him, no lights, engine dies. It had melted an inline plug in fuse in the wiring harness. It was an adventure finding and replacing the fuse (teamwork, one friend spotted the problem, another had a plug fuse) I did not know this fuse was there until this problem. What do I look for on this power drain to troubleshoot? Alternator? Voltage regulator? Something shorting?

[Nacho-RT74]

this is a common fail on Mopars.

it could be several reasons:
-Battery damaged.
-terminals loosen/dirty/rusted somewhere, commonly at bulkhead conector... even melted.
-ammeter wires loosen on the back ( studs ).
-Alternator damaged, usually Diodes burned or Rotor shorted or broken coil ( it could be also stator but this is very rare ).
-Of course, regulator damaged.

To check if is regulator, just feed directly the brushes ( bypassing the regulator ) from batt. If you get output, then is regulator. Becarefull and don't presss full teh gas pedal, just idle since with regulator bypassed you will get A LOT OF JUICE FROM ALT, and could burn some in the car.

To check alt rotor conditions, check for continuity between brushes. You must get between 5 and 10 Ohms. If is double field alt, also check between both brushes and chassis... it must be isolated. If is single field then check only on the wired brush.
Note about this... if you notice some short, it could be also brush isolator broken, not necesarilly rotor, check for that. Diodes are easy to see: a burned diode normally it's gone LOL.

Wires are easy, just unplug, clean and plug them again tight.

Ammeter, just check behind the dash and look at studs nuts if they are loosen.

BUt it could be just the fuse link damaged with continous overheating throught the years... that could mean alt is sending around the fuse limit to drive or plugs are dirty or loosen causing overheating on wires...

[jmanscharger]

Most of the wiring was redone by a previous owner and everything looks cosmetically good.  All the gauges work, including some aftermarket back ups below the dash. But anything that puts a diffrent drain on the system- if you shift in reverse radio goes out. I thought at first it had something to do with the reverse lights, found a wire grounded in the trunk. The starter also seems a little slow sometimes. The battery is 6 months old. I will start down the list this weekend Nacho. That plug in fuse didn't blow- it melted. I'm still thinking regulator?

[Nacho-RT74]

I only trust on wiring made by me... and EVEN ON THAT WAY...

[jmanscharger]

Yeah looks good but fuses don't melt unless theres a problem ... I emailed a local Charger friend who has more electrical expertise, we'll go down your list, he has testing equipment.

[Plumcrazy]

Sounds like you are running off the battery, no output from the alternator. That would explain the dimming lights.

The inline fuse problem sounds like a bad connection at the fuse.  Was the fuse blown? If not a poor connection causes high resistance that causes heat.   That would explain the melted connector, too much current would have blown the fuse.

[Nacho-RT74]

The inline fuse problem sounds like a bad connection at the fuse. Was the fuse blown? If not a poor connection causes high resistance that causes heat.   That would explain the melted connector, too much current would have blown the fuse.

That is my firts guess

[71_deputy]

 

[69bananabeast]

had the same problem back in the day , wiring was shotty and had splices everywhere , couldnt figure it out so re-wired whole car with no more problems . Although you said it had been wired by previous owner so I dont see why you would be having problems . Im not much for electrical but i'd check all the surrounding wires and see if they melted any look at all splices if there are any .

[jmanscharger]

If the alternator has been upgraded to a 65 amp and the fusible link going to the interior only has a 30 amp fuse could this be part of my problem? If we bypass the voltage regulator the alternator still puts out only 10 or less at idle on the aftermarket gauge. At road speed or high rev the alternator puts out 14 but if you "womp down on it" break and stop the 30 amp fuse over heats and the car dies. I want to try a new better fusible link, but should it have a larger fuse?

[Nacho-RT74]

definitelly no... you are talking about an aftermarket voltimeter, Voltage is able to run through any gauge wire, and the drop would be allmost unnoticeable, difference about gauge reading is related with amperes and reads on ammeter.

Voltage drops could it be regulator or damaged diodes on alternator... also somekind of short on alt.

In fact, mostly of aftermarket voltimeters gauges are 18 or even 20 wired

[jmanscharger]

The wiring around this fuse is spliced on both sides and under the dash and this fuse melted again, the fuse is on the engine bay side and overheats maybe from the engine bay heat. The wire plug itself is starting to melt. I have a new fuse plug to splice in, I'll go back with a 30, then it's back to checking the alternator. 

[Nacho-RT74]

if the problem with voltimeter reading is wiring then resistance problem on wiring because rust/melted/sulfated areas is GIIIIIIIIAAAAAAANT, but anyway easy to save.

[jmanscharger]

replaced bad wire. had alternator tested. Bad diode, looks like I'll be getting a new alternator, any suggestions?

[Chryco Psycho]

not a powermaster

[RD]

just curious, do you have a lead running off of your negative cable that grounds to your radiator core support?

[2Gunz]

Im not sure what your problem is.

However you need to remember that Voltage and Amperage are related.

Amps = Watts/Volts

So lets say that your car is drawing 350 watts of power. And that the car electical system is healthy running at around 14 volts.

350/14 = 25 Amps

On the other hand ........ The car is drawing 350 Watts , and the electical system has a funky alternator and only working at 9 volts.

350/9 = 38.8 Amps


As you can see a 30 amp fuse would be fine IF the car alternator is running correctly. However if the alternator is shot and the electrical system can only provide 9 volts then the Fuse ( and the prolly the wiring ) is to small.

Keep in mind that this is the math behind it and not a real world example.  In reality the spread is prolly much closer. 12.5 to 13 Volts with battery load and a working alternator. And a battery that has been in this situation for a bit at around 10 Volts with no alternator.

350/13 = 26.9 Amps

350/10 = 35 Amps

Also the 350 Watt figure I used doesnt mean anything I just picked it out of the air. It could be any number, depending on what you are running at the time in the car (headlights, tailights, radio, CB, Heater, whatever is on that fuse).

..........................................................................

Some more general electrical information that hopefully will help you sovle your problem.

Amperage is a funny thing. And it is directly affected by other factors. The two main ones are Wattage and Voltage. However amperage is also affected by resistance. Resistance in a nut shell is how much "work" the electricity has to do to get to where its going.  As the electricy runs into obstacles, it requires more of it to get where its going.  Think of it as your truck pulling the ole charger. On level ground its fine. But go up a large high and it will take more gas, or require a bigger truck.

So if you have bad grounds, small wiring, rotted wiring and lose connections your 20 watt lightbuld could be drawing 30 watts.

Resistance also creates heat (much like a space heater), heat creates more resistance and on and on. Untill finally something gives. Normally a fuse but in some cases the wire itself.

...................................................................................................

Personally I think you have a collection of a few things going on.  A bad alternator, with some wiring issues. With it leading up to you blowing the fuse in your car. To me the power dip and the fuse blowing are a logical chain of events. Voltage goes down amperage goes up and the fuse blows. Generally however things like that are factored into the design, so you must have other issues as well.

I would change the alternator, inspect the wiring and take a good long look at the amperage gauge in the dash. The design is junk to begin with and given that the car is 30+ years old its prolly toast.  I bypassed mine years ago after having electrical problems, and never replaced it.  Running all the cars power through a small gauge in the dash is a flaw IMHO. Which is also prolly why you dont see it in cars anymore. My dads lawnmower has one HAH.


Sorry for such a long post     It could be something as simple a loose wire. But it appears you have done the "easy" stuff and I figured I get into the hows and whys of it all. Hopefully this will somehow make a lightbulb turn on in your head and say "Oh ya its got to be the...."

2Gunz

[Ghoste]

If I can tack on to the end of what you just wrote there...
My car was showing some minor electrical problems among them an overcharge issue and a hard start on occasion.   There were a few other little bugs but just piddly stuff that would crop up.
Anyway, I have new wiring bumper to bumper, new electronic regulator, new alternator.   Everything said it should be fine.   I tried cleaning up every ground and every connection in the car hoping to lessen the resistance as 2Gunz has pointed out.
Today, I solved it.   I had one old part remaining.   It was a fusible link.   It wasn't blown but it was old.   I took it out on a whim and it came out green on the ends and just in crappy shape overall.   Put in a new one, and ta-daa!   So everything 2Gunz wrote about resistance affecting the total picture, was completely true in my case.