so i pulled the dash out of the 72gs last wknd in hopes of installing a 3 3 8 tachometer in the right section of the dash where there is a beauty plate currently. after digging the dash out, i noticed someone had taped two light bulbs together, along with a black v shaped electrical harness that has two or three wires in it (i'm not at home now to confirm). my question, can i use these wires for the tachometer? idk if there was supposed to be one in here or what these could be used for. any help in getting this thing in would be appreciated.
V shaped connector is for a factory clock. Two lamp sockets for the clock or a factory tach., as back lighting. Factory tach. needs a conductor from the - side of the coil to the tach.. Pick-up a ground at the dash area.
So since I'm putting a tach in the clocks place, could I cut this electrical conector off and use these two wires for power and ground and run another wire through the firewall for the - side of the coil?
modern syle tach from the local parts store. seems to be the cheaper way to go. factory tachs are rediculously expensive IMHO but worth it for the stock look i guess. since i'm not keeping a stock looking/running car, i'm down with saving a few pennies and going with my own custom look.
The clock connector has an orange=12V, black=ground. The light sockets are wired to work with the rheostat on the headlight switch to allow dimming. You'll have to know what the tach. manufacturer needs for a source from the coil. On an AC car you can use the firewall hole common to the vacuum lines & wiring harness for the AC system. About midway across, just below the voltage rectifier.
The tach I bought was one from autozone (sunpro supertach 2) and when I put the power and ground to it, the tach registers anywhere from 300-1000 rpm without the car even being on. As I start the car, it registers zero at first then moves to 12-1500 rpm as the engine idles. Do I have a bad tach? It registers zero with no power. I tried several power and ground combinations to include directly to the battery and the result was the same. Is this tach faulty or am I missing something in the wiring?
The tach came with four wires. Red(pwr) black(gnd) white(dimmer) and green(neg side of coil). That's the location I hooked up all of the wires. Even if I take the connection loose from the coil and hook up the pwr and gnd wires only the tach reads several hundred rpm
Sounds like the tach. is picking up a stray signal. Did you use the clock feed? The clock feed & ground are energized at all times, even with the ignition off & the key in your pocket. Try changing your 12V source.
Nope, that is normal for a lot of aftermarket tachs. I know my Autometer tach does the same thing. They even tell you in the instructions to expect that.
Thanks guys. I'll get a replacement just to be sure. Should I switch the 12v source from the orange clock wire? If so, to what? Hey Larr, does your tach read the same number everytime?
It reads consistently if you are talking about accuracy, but when I shut it down, the needle will stop at different numbers every time. I have an Autometer Tachometer. This is from the FAQ from the Autometer site. Why doesn't my tach pointer rest at zero when the ignition is off? We get a lot of questions about this. Here is the reason, along with some specifics for each product. Most of the electric instruments that we offer use what is called an air core meter. In layman's terms, this means there is no physical part to hold the pointer where it sits, or to force it back to zero when power is removed. It uses an electrical charge to return to zero when power is applied, and when a signal is fed to the instrument, the pointer will indicate the proper reading. This is normal, and no cause for alarm. The unit is not damaged or broken, it just doesn't look like most other instruments out there. For Example: The pointers, on most modern OE (original equipment) gauges, just hang there when power is removed. We use air core movement due to its rapid response characteristics, so when you stomp on the accelerator, the pointer is capable of showing you exact engine RPM.
Just looked at the instructions for your tach online. They say the same thing as Autometer http://www.tradervar.com/All Other Sun Tachs.pdf Look under "Zero adjustment and pointer position" at the beginning of page 2
Just re reading your posts. If you are using the 12 volt feed for the clock to power your tach, you will need to use another 12 volt switched line. The clock feed would have power at all times so the clock would work. What you need is an ignition on 12 volts that cuts out when you switch the ignition off. You can easily run a separate wire from the fuse block. You can either tap into a fuse that has ignition on power, or just plug into the accessory socket on the fuse block if it isn't being used. Use a test light to confirm battery voltage with the key on, and nothing when the key is switched off.
