Further to finding more information through links from good people on here I have retested the coil with my meter.
Setting the meter to 20K, in the OHMS range, (first of all touching the probes together to settle the reading) I now find the reading between the centre HT outlet and the + side of coil is "15.56".
Resetting the meter to 200K, (then touching probes together again etc) I find the reading between both the + & - of the coil is "0.00"
But I dont understand what the readings mean
Nor me!
Pete, what your doing is measuring resistance in the coils of wire contained within the coil body.
As Fifer says, the DLB105 is a 3 ohm primary resistance coil.
With all the wires disconnected from the terminals on the coil, switch your meter to the lowest OHM setting that it has then touch one prong of the meter test lead to one small terminal on the coil and the other prong to the other terminal, doesn`t matter what colour goes to which.
You should get a reading of between 2.7 - 3.2 ohms. anything outside this range will indicate a `bad` coil, but it may still work.
The primary winding circuit is the one that actualy creates high voltage from a smaller input voltage and is made up of thick copper wire, this winding very rarely fails.
The secondary winding is made up from thousands of turns of very fine (human hair width) copper wire, its the secondary winding that delivers the spark out of the coil and down the king lead to the dizzy cap.
I cannot find a given value for the secondary resistance, but somewher between 0.10 and 0.80 should be ok, what is more important is whether or not you get a reading.
So switch the meter to the next highest ohms range and then, one prong of your meter to the + side terminal and one to the king lead terminal, if you have a reading, you have a path for the `spark` to travel up.
In a points distributor the points open and break the electical circuit before the current reaches the secondary winding. Because there is a gap in the circuit, the current jumps the gap in the form of a spark and with the help of the condenser, the current falls drasticaly falls again.
Back to the test you did earlier, the sparking that you got when you touched the - side lead to earth is basically what happens with traditionaly points. When the points are closed, the negative circuit is completed and the spark has only one path to travel, up and out the coil.
When the points are open, the earth circuit is broken and the spark jumps the gap on the points.
I think i have a coil in the shed somewhere if you need pics of the testing process.
