Ballast Resistor FAIL

[billschroeder5842]

So my trusty Charger left me stranded today. Fortunately it was in my home town and only 4 miles from home. The Charger was doing just fine then then motor stopped with all other electrical working.

I did a diagnosis on the road side while waiting for my wife. I went home grabbed some tools and a spare ballast resistor and headed back. I did the swap and the Charger popped right off and I drove her home.

What would cause the  ballast resistor to go bad? I hear these little buggers fail lots so is there anything I can do as preventative maintenance? I just ordered a spare...just in case.

Thanks!

[D13vyl]

Hi Bill

I have a 68 charger and was wondering where you bought the ballast resistor, im looking at stockin up on spares at the moment as u just dont know when these things fail.

Many thanks

Rene

[ODZKing]

I keep one in the glove box

[wingcar]

Many years ago I was driving my 1970 Charger down the freeway when all of a sudden the dome light bulb exploded.  This was followed by the quiet as my engine shut down.....yes, the ballast resistor had failed.   It seems as if the dome light must have had the least resistance and therefore blew out first.   The reason for the ballast resistor fail was obvious after opening the hood and finding it "oil soaked" and dripping with oil.....my front seal had been leaking for a time and decided it had had enough and let go.  After cleaning up the engine compartment and replacing the ballast resistor the Charger started right up.  And, yes I replaced the front seal shortly after this.....................lesson learn:  oil and ballast resistors do not mix. 

(By the way, I alway carry a second ballast resistor in the trunk)

[Chatt69chgr]

Aftermarket ballasts are available at any parts store.  They don't look exactly like the original from a physical standpoint.  A reproduction of the original two terminal ballast with correct numbers on it is available from Mancini.   

The ballast is just a wirewound resistor.  Too much current through them will heat them up such that they will eventually fail.  They form part of a circuit which includes the coil primary.  The idea is that when the car is in the run position, the voltage to the coil is 9V.  I would think that if the coil primary shorted or partially shorted then the resistance would be lowered increasing the current through the ballast which, in turn, would heat it up causing it to fail.  Also, if a coil that had too low primary resistance was substituted for the correct coil then that would essentially do the same thing.  Obviously, these ballasts are not seal against the environment so water soaking into them or oil would probably reduce their current carryiing ability----there again causing them to fail do to heat buildup.

[hemi68charger]

I get the resistors from my local auto parts store and just replace the bracket with the original. I'm sure if someone wanted to, they could get the ohms drop and create a solid state version.

[Rolling_Thunder]

I get the resistors from my local auto parts store and just replace the bracket with the original. I'm sure if someone wanted to, they could get the ohms drop and create a solid state version.

Sounds like a fun project...       anyone know the factory ohm drop?

[hemi68charger]

I get the resistors from my local auto parts store and just replace the bracket with the original. I'm sure if someone wanted to, they could get the ohms drop and create a solid state version.

Sounds like a fun project...       anyone know the factory ohm drop?

If noone's piped in before I get home, I'll look in my factory Service Manual. I believe it is discussed in there.

[terrible one]

  Think it's 1.2 ohms but someone find out for sure!

[Chatt69chgr]

You could drop the voltage from the charging system to about 9 volts at the coil by using 7 Silicon Diodes in series in place of the ballast (0.7 Volts each).  They would need to be able to handle the primary current.  If the coils are about 1-Ohm and you have 9 Volts across them then the current would be about 9-Amps.  You would want your diodes to handle at least twice this amount.  The ballast is a much cheaper way of getting the required voltage drop.  They probably burn out mostly because they are probably not rated for a high enough Wattage.  If they dropped 5 volts and you ran 9 Amps through them they would be dissapating 45 Watts.  Just from their physical size they look like they are awfully small to be dissipating this amount of current. 

[aussiemuscle]

australian valiants used the same design ballast resistor. i blew two in the four years i owned that charger. (second time around i knew to check it) 

[Plumcrazy]

The resistance through the ballast resistor varies with current flow which varies with engine rpm.  This naturally causes the resistor to expand and contract from heat.  That's why they eventually fail.  If they are still available I would buy one from your local dealer. I am not a fan of aftermarket electrical parts. The quality is too hit or miss.

[skip68]

I had 2 that failed and they were new.       
Cheap parts made in China.  I now run MSD and bypassed the ballast.   No more problems.     

[hemi68charger]

I had 2 that failed and they were new.      
Cheap parts made in China.  I now run MSD and bypassed the ballast.   No more problems.    

I sort of did that. I have a Pertronix Ignitor II on my Daytona. I changed out the ballast coil for a straight wire in between the two spades inside the ceramic housing.. Works great as well.

[Brock Lee]

It pays to keep spares as well as spare voltage regulators, a coil and fuses in the console.

[BrianShaughnessy]

I've had the same MSD 8214 ballast resistor for years.      It's .8 ohm.    Works good.

The stock resto type look like the same crap parts store ones that have been failing for over 40 years.

[resq302]

I keep one in the glove box

yup, same here!

[Cooter]

I had 2 that failed and they were new.       
Cheap parts made in China.  I now run MSD and bypassed the ballast.   No more problems.     

ZACTLY!

[KS71owner]

I went through several when I first got my Charger.....I too learned the value of keeping a spare one in the glovebox.   

After I switched to electronic ignition and new wiring I had no more problems. Also probably because it got relegated to occasional status and was no longer a daily driver.

[Chatt69chgr]

Most wirewound resistors are made of nichrome wire wound around a ceramic bobbin and coated with a ceramic compound.  If the starting resistance of the ballast was 1.2 Ohms at a temp of 80 degrees F and it was increased to 400 degrees F due to heating it's resistance would increase to about 1.28 Ohms.  Not much of a change.  As the wire heats, the resistance increases thereby lowering the voltage at the coil which would be undesirable I would think.  I would agree that heating of the wire causing it to expand and contract which, in turn, would cause the outer layer of ceramic to crack off exposing the wire to the elements is probably the cause of them failing.  I can also see how increased rpm would increase the current flow through the resistor causing it to heat up.  I think that the ballast was marginally acceptable from a power dissipation standpoint.  Were a larger resistor (ballast) designed to handle the heat load been  originally specified then I doubt that these would fail very often.  Aftermarket suppliers probably just copy the original design.  And I doubt that Chrysler makes these.  They go out on the open market and have them made by someone.  Probably to their original specification. 

[ACUDANUT]

 How hot is too hot, when you touch these ?

[billschroeder5842]

Funny but the spare I installed had a "closed" back side with some sort of filler to cover (protect?) the wire. My old was was open and when I examined it I saw a burnt wire.

Any different between the clsoed and not closed? I ordered a spare and all I coudl find was the open model.

[GreenMachine]

No need to carry a spare, just connect the 2 wires together, it'll get you home. It's bypassed while starting your engine anyway. I've heard if you leave it like that for too long though, it could burn up the coil.

[ACUDANUT]

 Does the car that had a B.R. fail have electronic ignition. ?