Trouble Shooting
Now that you have the best ignition available for your Classic car you will no doubt want the experience to be the best. So why not make the ignition system the best it can be by adding new plugs, wires and a coil of not less than 1 Ohm.
My old distributor works but the 123 does not.
1.) Disconnect the original wiring from the coil +ve and -ve. Both the tachometer wire and the distributor feed wire. Leave the 123ignition connected to the coil as directed. Now run a jumper wire directly from the fuse box picking a 12v non-keyed power supply and connecting it to the positive side of the coil. Note: if it starts you will need to disconnect the jumper wire from the source to turn it off.
This will take the 123ignition out of the ignition circuit in the car. If there is too much resistance in the original primary circuit it will cause the symptom you are experiencing.
2.) On some Mercedes there is a brown ground wire that goes from the coil negative to ground. This wire will need to be disconnected.
3.) If your static time is too far out. It will not fire. Try advancing or retarding the timing by physically rotating the distributor until it fires.
4.) A lot of problems are caused by a bad primary ignition circuit, specially high rpm problems. This means the circuit: Battery (+) --> Contact switch --> Coil (+) --> Coil (-) --> Ignition (black wire) --> Ignition to ground (minus (-) of the battery must all be in top shape.
This total circuit has a very low resistance. For example 3 Ohm when you use a Bosch blue coil or 1,8 Ohm with a Bosch red coil.
You will get a weak spark when there is a bad connection (resistance) somewhere in this circuit (for example a bad contact switch or a bad connection between the ignition and the battery (-).
5.) Never trust old coils as they may have been subjected to overheating which would damage the coil.
6.) Most cars are well along in years and have had multiple owners. Often what you see in the wiring is not always correct. Make sure the correct wires are going to the +ve and -ve side of the coil. While the car may run with the old points if the wires have been crossed it can keep the 123ignition from functioning properly.
7.) Take the red wire off the coil positive and connect it to the switched side of the fuse block. This also solved a tachometer issue on a customers car.
8.) Weak Spark, Use a good quality spark plug wire if you have a weak spark. Check all connections in the ignition circuit for bad connections. I would check the voltage of the coil under load. We cannot over emphasize the need to have good connections everywhere. Also check the GRND and try another coil.
9.) Re check your wiring. On TUNE models the Blue wire (curve 1) goes to a good ground. The yellow wire goes to a power source (6 or 12v) and when it is energized provides curve 2.
10.) To check if the 123 works in the car, keep the coil connected to the 123. Connect the coil high tension directly to a spark plug. Make sure the plug is grounded. Crank the motor and look for a spark. Note that this test will only work if the spark plug and the coil are in good shape.
MGB Related Issues with Smith's RVI Tachometers
If you have found some helpful hints for unforeseen installation issues, please share them with me so I can post them here.
Thanks
Ed