Ok so I went out to start my 71 Duster this morning and although it winds over strong she wont fire. Was running fine a week ago when parked. I've been over everything I can check with a meter and all conections seem ok. Having spent some time searching the forum for answers I have read a number of things I'd like to clarify.
1 If the voltage on the coil when ign on + should be just below battery voltage - should be less than 2v ( I have 10.5 on positive side and 8.5 on negitive side)
2 ballast resistor is a 4 connection one. one side is supposed to be 5ohm the other 0.5 ohm. When measured we dont even come close to these readings. in fact one side I cant get continuity.

So question time, will the ballast resistor prevent the car from starting if its non operational.
Do the ignition modules fail
Do I need a ballast resistor if the car has breakerless ignition

 

No continuity is burnt out (open) ballast resistor. Needed on almost any ignition to supply reduced voltage to coil while running.

When the key is in "start" a higher voltage is supplied to the coil to compensate for the voltage drop created by the starter motor when it is cranking.

Ignition modules do fail but try the ballast first and buy two to keep one in car for any future failures.

 

If you are certain you measured the ballast correctly, it is bad. The ballast is in reality TWO resistors in one "box" and one of them is the same (or close to same) as the older breaker points resistor. In other words, one terminal to the other "the long way" down the length of the resistor

Your voltage readings are confusing

Your situation gets "more confusing" because you could have 1 of three conditions..........

An original 5 pin ECU with correct 4 pin resistor

A newer 4 pin ECU which DOES NOT NEED a 4 pin resistor, and so you could either have a 2 pin or 4 pin resistor.

So if you have a newer 4 pin ECU, the "second half" of the resistor is not needed

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With key on "in run" the coil PLUS should be somewhat below battery, showing current through the coil and resistor. This might be anywhere from 5-9 volts, assuming battery is "up."

If you move your meter to the "ignition run" wire on the resistor, IE the incoming power, this should be "same as battery."

If you measure coil NEG, this should be very low, perhaps 1/2 to 1 1/2 volts. This shows the coil is drawing current, the ECU is at least passing current, and is grounded.

The ECU MUST be grounded.

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With 5 pin ECU / 4 pin resistor circuit, a bad balllast can CERTAINLY prevent the vehicle from firing.

With the newer 4 pin ECU and either 2 or 4 pin resistor, things are "different". What happens here is that the bypass circuit in start will FIRE the car for a moment, and when the key is released to "run" the engine will die. Often guys "play" with the switch to find that it will run. This is hard on the switch, and bypasses the resistor.

 

Ok double checked things after some more research, the coil reads ok but the ballast resistor the top two pins show no continuity while the bottom two read continuity and the correct 0.5ohms. It doesn't look like the four pin resistors are available down here in NZ. so I'm going to have to buy in from the states and wait two weeks for them to arrive

 

found a two pin resistor and used it to replace the side that wasn't working, car runs. Now to order 4 pin ones

 

Leave the ballast hanging there for originality looks only and get a coil that doesn't require that piece of crap. The coils probably about the same price as the ballast and you won't have to worry about that issue again.

 

No. Sorry. Wrong. There is a VERY good reason the design used a ballast. People bitch about ballast resistors going bad but the fact is that I've replaced no more than "maybe" one or two over the years from 70 something to present, and "in a previous life" I sold auto parts for about 17 years. I don't recall that we sold them by the "basket load"

 

^^^^

 

I agree with Dodger on this one.......

 

My mistake. Their longevity is probably why they don't use them anymore.