I have wired a tach into my 51 fleetline with a 235, which has a 12 volt conversion. the tach seems wonky, but I took keyed power off the + side of the coil. Would it work better if I took keyed power off the keyed power from before the ballast resistor? It is works perfect below 2000 rpm but if I go above 2000 rpm and let off the needle stays for a second then drops and other strange habits.
Not sure how the tach could work powered from keyed power before the ballast. All tachs I've ever used or known of come off the negative (distributor) coil post, on negative ground systems. Make sure the tach ground is back to the battery.
well, it could be that I have a bad ground, I grounded the tach to the dash. I thought a good ch***is ground would be suficient....
I was trying to find easily accesible keyed power without digging under the dash too much, power to the coil is keyed power, the ballast drops the voltage to 6-8 volts, perhaps my problem with the coil is the feed into it, seeing as the negative side of the coil is the sensing signal for the tach. I am not using an internally resisted coil, so it has a ballast resister externally.
A Ballast Resistor is an electrical device that is installed in an electrical circuit to provide resistance to the flow of electricity in that circuit. In this specific case, the resistor is installed between the primary voltage source for the ignition coil (the wire that comes from the ignition switch) and the coil (+) stud. With the resistor installed in this manner, the coil no longer sees full system voltage but rather it sees about 2 volts less. Additionally, the current p***ing through the coil is reduced about .5 amps.If your tachometer requires a full12 volts switched voltage then hooking it to the positive side of the coil will not provide it.You need to find another source for your 12 volt switched supply.
The cigarette lighter is often an easily accessible unswitched power source and the radio a good switched one. Does your conversion include a fuse panel? Often they will have several accessory lines available.
Well it needs 12V for keys power if t is a 12v tach, what does a ballest resistor do? It could be that your problem is compounded by a cheap or woky tach, but it needs 12V for keyed power and that would be before the ballast resistor.
There's been some confussion (mostly mine ) but some tachs require full keyed voltage, 6 or 12V, along with a trigger, which would be the dist. side of the coil. Most tune-up tach/dwells only have two leads, for the coil and ground. You still need a good ground.
The Jalopy Journal
