Faulty ballast resistor?

[GlenwoodCJ7]

Had a no start issue and checked that I was getting fuel from the pump and all checked ok. Checked the voltage at the coil and was only getting 3.5 volts. I have a ballast resistor in line and get 12v on the hot side and only 3.5 on the side going to the coil. I assume that is the problem. I use to get 9 on that side. I have the mallory unilite. Would you say that is a correct assumption?


Thanks

 

[k-2]

fuel from pump? with a carb ok - FI mist have PSI checked.

I agree That is a lot of voltage drop, and your past readings of 9v seams to condemn ballast.
My only thought is I do not remember a ballast failing higher often going open - but a 6$ part and testing vs R&R just get one.

for testing only jump 12v past resistor - does it start?

 

[superj]

i agree. run a jumper just to test

 

[RestorationRides]

I agree too. The voltage should be somewhere closer to 6v to 7v if I remember right. This is based on the fact that most coils wereb designed along the lines of the original six volt car systems.

But, one thing that's important to note, and nobody's mentioned so far, is that in cranking mode the ballast resistor is normally bypassed giving you the full 12+ volts - providing some extra power at the coil just for that brief period of starting.

Thought:

Check to be sure that you have a good grounding between chassis and frame and engine. A faulty ground would, to that electrical circuit, appear as additional resistance beyond the calibrated value that the ballast resistor is designed to deliver. Additional resistance would yield a greater voltage drop across the resistor then would be expected...

Another thought:

Be certain that the coil that you're using is a non-ballasted coil. A ballasted coil has the internal resistance so that an external ballast resistor is not required. If you use an externally ballasted resistor on an internally ballasted coil, you'll have too much voltage drop and very little power at the coil... :-(

Regards,
Restoration Rides ;-)

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