Guage again?

[Zcliff89]

i nervously really want to run a tach in my vic as i have posted before but, dont want to screww anything up! I went into autozone one day and all they had was a tach no wires for instal? Where would i find them and how the hell would you tap into the coil? what would you have to do?
I have also looked up that one guy who has all the instructions to do it too

[P72Ford]

The tachometer install is very easy; do not be afraid of it at all. Even if you've never played with auto electric before, its not that serious.

Every tachometer should come with the gauge, some kind of mounting mechanism (unless its totally "in dash"), as well as some pig tails (wiring leads) out the back of the tachometer itself. Most tachs I've played with have a red, a white, a black, and green wire at the back. That may be different depending on lighting, etc. (I am familiar with the Autometer gauges, as well as Sun products.)

In my experience, the black is a ground, the white is for illumination, the red is a switched 12V source, and the green is the sender. The ground is simple. Put an eyelet terminal on that wire, and ground it well somewhere under the dash. For the white wire, you have some choices. If you don't want lighting, leave it unhooked. If you want it on all the time, then hook the white wire up wherever you hook the red wire (I'll get to that). If you want the tach light on when the dash lights are on, you'll have to find an illumination source. That is easily found at the radio, or ash tray light. You'll need a test light; flip the lights on and off (with the test light well grounded) until you find a wire that lights when the lights are on.

For the red wire, you need a switched 12V source; a source that is only available when the ignition is on. You'll need the test light again for this. My tach is wired into some wire under the dash near the brake pedal. I found it by turning the key on and off, and checking to see what wires were hot when the switch was on. Make sure the wire is only hot when the switch is on, and not a constant 12V source.

The green wire needs to be run through the firewall (should be some place where you can go through near the brake booster; use a grommet). Since your car is most definitely like mine (carbed P72), this step may be different from you. The green wire needs to go to the "tach" terminal of the coil (my "horseshoe" clip on the coil says "tach" right on it). If your car is injected, the coil is a little different I think, but it still may say "tach" Hook the green wire there. I chased the "tach" wire back to a vacant plug on the drivers inner fender, and picked up the tach signal there. It is fine to do either way.

You may need some extra wire (to go through the firewall, etc). Make your connections well (I prefer to solder the connections; butt connecotrs should be ok if you do them right).

The hardest part is finding a place to mount the tach. I have mine mounted on the A pillar, and it is surprisingly low profile, and difficult to see outside the car (I like it like that). You can always use the steering column, or browse the readers ride section and see what clever ways others have devised to mount their tachs.

It is a good idea to get an inline fuse, and mount it in your switched 12V wire. That gives you some protection if something goes wrong (not that it will; but the fuse is cheap insurance). You can get that fuse at any parts store.

Its not a big deal though, so don't be afraid of it. Once you get it done you'll be glad you did it. Good luck.

[Glen]

It really is easy to do. Nice write up on how to do it.

[Zcliff89]

Thanks alot that helps a TON! But the coil wire can it be just a normal elctrical wire or no?

[Glen]

Yes it is, you should have 3 wires on the coil, 2 little ones and 1 big one. The big one goes to the dist. and comes out of the middle of the coil. You want the little one, if you have the newer one (square coil) it will have a plug with 2 wires and will it should say "tach test' or something like that on it. If you have the older one it will be round and have 2 studs on top, one will have a " - " the other will have a " + " mark on it. I think you want to use the "-" one.

[91waggin]

Maybe it was just my tach, but I found that it didn't work unless I grounded it directly to the battery. It would do all kinds of crazy things, like move backwards when you applied power to it, if you didn't ground it directly to the battery.

What you can do to figure out where your tach signal wire goes is start the engine, then open the hood and put the red and black wires directly onto the positive and neg terminals on the battery. Then you can use the green wire to probe around and find the right terminal. Once you think you've found it, reach over and open the throttle a little ways and make sure it behaves properly.

[P72Ford]

Maybe it was just my tach, but I found that it didn't work unless I grounded it directly to the battery. It would do all kinds of crazy things, like move backwards when you applied power to it, if you didn't ground it directly to the battery.

My Autometer was like that; I thought it was broken or something. But, when I cleaned a ground area (with a scotchbrite pad), and grounded it again near the firewall, it was fine. I guess the first time I didn't have a complete ground.

[91waggin]

In the manual for my tach it said that any ground other than the battery can be electrically noisy and confuse the circuitry in the tach. Whatever works, though!