Tach voltage

[JamieZ]

Trying to trouble shoot my tach and discovered the +12V (long stud) is actually a shade over 14V when the car is idling. Is this normal or is it something I should be concerned about? Or is this normal while the car is charging?

 

[JamieZ]

I switched out the Voltage regulator..no change still high (14-16v). I switched the ballast resistor. No change. I already may have smoked a tach. Any ideas on this?

 

[SwedCharger67]

It's unclear what car and ignition system you have, and exactly what signal you are measuring.

Generally speaking the voltage to the tach is originally coming from the negative side of the ignition coil, and this voltage is a very ugly square wave.

Usually you can't measure this kind of voltage with a standard multimeter, since they show the correct voltage only if you have a pretty sine wave, or a pretty dc voltage. It should however show something that is somewhat close to the actual voltage.

Your measured voltage to the tach seems high assuming you are measuring the signal that should come from the negative side of the coil.

A battery that needs charging can take over 14.4 Volts without problems, but a fully charged battery should never see above 14.4 Volts (starts developing explosive gas).

 

[JamieZ]

I have the stock points ignition on a 1968 charger. I am not measuring the signal connection of the tach (which is a spade connection back to the - Side of the coil).

i am measuring the connection on the long stud. This looks like it comes from the ignition switch if I am reading the wiring diagram correctly.

 

[JamieZ]

I just checked, with the engine running my batt is around 15.5v that seems like it is overcharging?

After a few minutes it was up to 16V. I just replaced the VR with a new one...so maybe there is an alternator issue? I'm not entirely sure how to troubleshoot that/verify that it is the alternator.

I guess I could buy another VR in case I happen to have 2 bad ones.....