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I seen a car the other day that had the orange wire hooked to the + side of the coil and the black from the 7531 to the - side of the coil and another wire on top of the black wire going to the motor as a ground. My question is why and also what would this do?
 

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I seen a car the other day that had the orange wire hooked to the + side of the coil and the black from the 7531 to the - side of the coil and another wire on top of the black wire going to the motor as a ground. My question is why and also what would this do?
The HVC coil paper work says to ground the coil, never seen anyone do it that way though.
 

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The high “+” voltage arc in the plug gap obviously must have a “-” or “ground”.

The coil secondary and primary windings are connected inside the coil. One end of the secondary winding (HV output) goes to the plugs and the other end of the secondary winding is “grounded” to the coil primary winding.

To “ground” the spark energy, the black wire connects the coil primary – to the ground loop in the CD box and from there, through the large black wire to the battery neg. terminal, then from the battery neg. terminal back to the engine block by the “ground” cable.

Use an Ohmmeter to measure resistance from the CD box small black wire (coil neg.) to the large black ground wire to the battery. You will see they are common, there is no resistance.

Rather than send the ground energy through the convoluted loop all the way to the battery and back with all the resistance and capacitance (that is the biggest energy loss) and potential locations for a poor connection, it is obviously more efficient to connect the coil ground directly to the engine.

The high “+” voltage arc in the plug gap obviously must have a “-” or “ground”.

The coil secondary and primary windings are connected inside the coil. One end of the secondary winding (HV output) goes to the plugs and the other end of the secondary winding is “grounded” to the coil primary winding.

To “ground” the spark energy, the black wire connects the coil primary – to the ground loop in the CD box and from there, through the large black wire to the battery neg. terminal, then from the battery neg. terminal back to the engine block by the “ground” cable.

Use an Ohmmeter to measure resistance from the CD box small black wire (coil neg.) to the large black ground wire to the battery. You will see they are common, there is no resistance.

Rather than send the ground energy through the convoluted loop all the way to the battery and back with all the resistance and capacitance (that is the biggest energy loss) and potential locations for a poor connection, it is obviously more efficient to connect the coil ground directly to the engine.

There is potential for trouble with this if the main battery ground cable is disconnected and he CD box remains connected, such as might happen if a cut-off switch is in the battery ground cable or if a person forgets to connect the engine end of the ground cable and the CD box is connected directly to the battery terminal. In such a stupid case the car is still grounded through the CD box and using the starter will release the smoke from the box.
 

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I was having noise on my crank trigger with a HVC2 coil and MSD suggested grounding the negative side of the coil to one head and then loop a wire from that head to other on and then to the chassis. This fixed my noise problem, so I do this always now. This is with fuel injection, so low noise is very important.
 
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