Re: need help! testing and installing motorola cd modular
Unfortunately, you need the Merc-O-Meter or Merc-O-tronic---whatever----tester to test the CD unit.
However, when they fail it is usually one of two modes -- No spark at all, or Continued sparking.
There is a transistor within the unit which signals the capacitors to dump their charge into the coil. If this transistor fails, or if the capacitors short out, there will be no spark. Also, the transistor can fail in such a manner that it constantly signals the capacitors to dump. Then you get a constant spark.
As a 1978 with Motorola ignition, you have the electronic distributor with an electric eye and shutter. There is no way to test the electric eye. BOY! I'm really being helpful here! LOL.
However, you can perform some diagnostic tests. You need to check that the CD box is getting 12 volts through the blue wire from the ignition switch. you also need to determine that the electric eye is getting 12 volts from the blue wire on the distributor. THEN: as you turn over the engine, you should see low voltage --maybe 1/2 volt--on and off from the white and black terminal on the distributor as the shutter alternately blocks and unblocks the LED in the electric eye. This voltage signals the transistor inside the CD box to dump the capacitors into the coil.
The LED inside the distributor must be grounded, so check that the ground screw has not vibrated out and that the ground wire is not broken. While you are at it, the distributor is isolated from ground so be certain that the black ground wire from the distributor body to the mount is present and unbroken.
