Because the normal ignition system works by applying ground to the coil to allow it to saturate with current and then remove the ground to collapse the field and release the voltage through a multiplying coil, causing a sharp rise in voltage and reduction in amps to produce the necessary spark voltage needed at the plug. Since the ground is connected to either the points/condenser or electronic ignition you will either damage the module or cause an errant spark. Simply depriving the coil of power eliminates any of these worries and takes that entire side of the system out of the loop. The tach reads off the ground side causing a reaction to the multiple grounds buffered to raise the needle in response to the total grounding offered, which the face changes to rpm (through a knowledgeable calibration).
By using a diode you prevent power or ground from traveling one way, towards the coil on the other side, while allowing the ground to travel to the coil to provide for the necessary signal to read rpm. Radio Shack carries some fast acting diodes that will prevent the "cross talking" of the two coils and can be soldered in line very easily. Make a Y line to each coil, and after the y closest to the coils, solder in the diode paying attention to the provided diagram on the package for direction of current flow allowed. ALL DONE! Now the tach will read on both coils. The selector switch already in the system will choose the coil and the tach will read correctly. Colin Rainey Independent Loan Officer Branch 2375 Apex Mortgage Company 386.615.3388 Home Office 407.739.0834 Cell 407.557.3260 Fax [email protected] <mailto:[email protected]> -----Original Message----- From: [email protected] [mailto:[email protected]]On Behalf Of [email protected] Sent: Tuesday, October 10, 2006 4:37 PM To: [email protected] Subject: Re: KR> Tach hook up question. why can't you cut the power to the coil? Same effect and grounding the coil. Ray Lee kr2 9763 _______________________________________ Search the KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp to UNsubscribe from KRnet, send a message to [email protected] please see other KRnet info at http://www.krnet.org/info.html
