Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Morgan 4/4 1600 1972 - electrical issue

Ballast resistor is mounted on the inner wing near coil, its a small ceramic oblong about 1/2' wide and 2" long

Arwyn

Mine was right next to the coil. Follow the wire from the positive terminal until you find it.

Thanks - I have that wiring diagram but it doesn’t seem to tally entirely with the car!

That's fairly normal with Morgan's as you will have gathered.

Good luck.

Using the guidance offered, for which thanks, I’ve come to the conclusion that I don’t have a ballast resistor. Wires from the coil connect to the distributor or straight into the wiring loom which disappears (or appears, depending on which way you are tracing it) into the bulkhead by the fuse box.

Not sure what this means for the spec for the coil, if I’m to replace that, but if I can get it off I might be able to find some identifying codes on it.

Mark

I wonder if you've got a 9 volt coil and, as Arwyn suggests above, someone's removed the ballast resistor in the past leading to 12 volts going permanently through a 9 volt coil and the coil overheating. This could explain why the car fires when it cools down.

If it's a Lucas coil it should have something stamped on the bottom.

Ballast coil is usually rated at 9 volts whereas non-ballast is 12 volts. Often, there is a label saying “use with ballast”. If no identifying marks, there are two alternatives. Have a multimeter ready, set on DC voltage range, and switch on ignition, but do not start engine. Measure voltage between + terminal (or “sw” terminal, if so marked) on coil to earth. If it’s a ballast type it should read about 9 volts; if not then 12 volts or so. Alternatively, disconnect small wires from coil and measure its resistance across the two small terminals. A 12 volt coil will be about 3 ohms whereas a ballast one will be about 1.5 ohms. (Approx figures, as the test leads themselves will present some resistance depending on length and diameter.)

[/quote]
Ballast coil is usually rated at 9 volts whereas non-ballast is 12 volts. Often, there is a label saying “use with ballast”. If no identifying marks, there are two alternatives. Have a multimeter ready, set on DC voltage range, and switch on ignition, but do not start engine. Measure voltage between + terminal (or “sw” terminal, if so marked) on coil to earth. If it’s a ballast type it should read about 9 volts; if not then 12 volts or so. Alternatively, disconnect small wires from coil and measure its resistance across the two small terminals. A 12 volt coil will be about 3 ohms whereas a ballast one will be about 1.5 ohms. (Approx figures, as the test leads themselves will present some resistance depending on length and diameter.) [/quote]

I've performed the first of the tests you've described and I have 12v on the meter, so no ballast resistor.

I spoke to Melvyn to be sure I'm getting the right replacement coil and other bits whilst I'm at it, but for now, the car is running well. Just a bit reluctant to head off on an 800 mile trip without doing the easy things to avoid a repeat of the problem (not that there aren't other things, of course).

[/quote]
I wonder if you've got a 9 volt coil and, as Arwyn suggests above, someone's removed the ballast resistor in the past leading to 12 volts going permanently through a 9 volt coil and the coil overheating. This could explain why the car fires when it cools down.

If it's a Lucas coil it should have something stamped on the bottom. [/quote]

With the wonders of a smartphone to hand I've been able to read the numbers on the bottom of the coil - BN-16 HPC 101 12V - but as they predate the internet age by about 30 years not surprisingly a search doesn't bring up an ebay listing! However Melvyn R is on the case.

That's good news it sounds like you're nearly there Mark, well done we all learn a bit more as we go along.