'62 Ballast Resistor Help

[Bill O.]

I need your help again.

The Vette always runs great with the exception of spark plug wires occasionally jumping off. But within a day after I replaced a perfectly good Delco replacement Ballast Resistor with a used original (NCRS judge pointed out that it needed "round shoulders") the car started running rough, buck jumping at even speeds and backfiring on acceleration. One friend tells me that a bad Ballast Resister can fry the points....if too much voltage is passed through. Another says a BR either works when the starter is engaged or it doesn't...like a off/on switch....that the description of the problem suggests the points are burned, maybe by leaving the ignition on with the points closed (I don't remember leaving the switch on). Still another friend suggested I put the old BR back on and that the problem might go away since the car has not been driven much with the "new" BA.

I put the old BR back on and the problem still exists...but seems to have moderated some. I even replaced my old 091 coil and put on a service replacement I had. Made no difference.

I'm going to replace the points because I can see "black" on one side of the contacts, and we'll see what happens. But even if this corrects the problem, any ideas what caused it to begin with?

As always, my thanks for help and advise.

Bill

[Mike M.]

Re: '62 Ballast Resistor Help

the function of a BR is all or none. that is, it either works or doesn't. i suspect you've cooked the points, either by leaving the ign switch in the on position without the engine running , or the ign switch, solenoid, BR, coil wiring is incorrect. mike

[Bill O.]

Re: '62 Ballast Resistor Help

Thanks, Mike. The wiring has not changed on any of those parts and the wiring switch from the old BR to my the new "original' one was exactly as it had been. Soooo, switch on, motor off, points closed must be the culprit. That means I should be OK with putting the new original BR back on the car after she's running well again.

Bill

[Duke W.]

Re: '62 Ballast Resistor Help

Use a good digital multimeter to measure ballast resistance at room temperature. GM used both 0.3 and 1.8 ohm ballasts.

I believe all '62 Corvette engines had the 0.3 ohm ballast as OE, which yields greater primary current (for more secondary spark energy), but it was tough on points.

As a running change for the '63 model year, the 250/300-HP engines were equipped with the higher resistance ballast along with the ...087 coil. SHP/FI engines continued with the 0.3 ohm ballast/...091 coil through the '64 model year.

If the ballast fails, it should fail open - no ignition. The way it is designed it would be very difficult to fail short.

Duke

[Bill O.]

Re: '62 Ballast Resistor Help

Duke:
.
Is this an accurate summary?

" When the engine is running, you can get by with a lot less current at the points. That's the purpose of the ballast resistor. If the points were to receive full battery current/voltage at all times, they would only last a few hundred miles before needing replacement.
At the time of cranking (when the starter is operating), a separate wire gives the points the full 12 volts, bypassing the ballast resistor. When you release the key from "start" to "on", all the power to the points now has to flow thru the ballast resistor, preserving the points. If the BR fails, it fails "open" causing the engine to shut down....meaning no juice gets to the points"

It also seems unlikely that in less than 10 miles, my new "original" BR could ever be responsible for cooking the points or otherwise adversely affecting the run quality of the engine. BUT, what would happen if my new "original" is a 1.8 ohm BR (rather than the expected 0.3) hooked with a 091 coil?....too little juice to the points for smooth running? (assuming the points are not toast)


Thanks,


Bill

[Duke W.]

Re: '62 Ballast Resistor Help

That pretty much sums it up. At idle and low engine speed the coil is "saturated" i.e. current reaches the steady state DC value. The lower resistance ballast yields greater steady state current.

As revs increase the points are not closed long enough for the steady state DC current to be achieved, so spark energy is reduced, but the lower value ballast yields higher current at high rev for more spark energy.

The points in my SWC burned after about two years, but it never happened again, and I was never aware of the '63 TSB on the subject until the eighties.

It's a particular problem in cold weather, because the ballast's resistance lessens as its temperature decreases. The ballast heats up after startup, which increases its temperature - and resistance.

Again, the most important data is to know the actual resistance of the ballasts you have.

Duke