Chevy Impala SS Forum banner

1 - 7 of 7 Posts

5 Posts
Discussion Starter #1
I have a Sun tach that I want to install on my 95 SS . Can someone please tell me where to connect the wire to fuse box or where does it go.

Super Moderator
5,876 Posts
That tach can use a connection off the coil. Pin A13 on the red connector of the PCM also provides tach signal.

Premium Member
605 Posts
Run to an ignition switched power lead/circuit.At fuse box left side of dash,etc... For illumination,the ash tray light works well for switched gauge lighting. For ground good place is behind driver side lower kick panel. The tach signal,for 94-95 you want the negative side of coil which is the white wire with black stripe at coil plug.Or simply run it out to red pcm plug pin A13 as Jay said, which I like to do.

12 Posts


Installing the tachometer allows you to monitor engine RPM, a feature that is sorely missed by
some 94-95 owners. Other gauges can be installed in '96 models to monitor oil pressure or voltage


You have to install a non-factory gauge in the interior of the car. It requires some cutting of
(replaceable) interior pieces.

Parts Required:

· Replacement black dashboard instrument cluster bezel (P/N ???). Optional, but good
insurance. About $15.

· A 2 1/16" tachometer. A Cyberdyne unit is about $50 from JC Whitney or Summit. It has
two red digits indicating RPM and goes totally black when the engine is off. JC Whitney
also carries a 2 1/16" analog unit for $21 that fits. It has a backlit white and green display (a
little dim for some, but it works fine). No matter what you get, make sure it is at most 2
1/16" wide and no deeper than 3 1/2".
· 18 gauge wire and a length of black ribbed wiring conduit. About $5.
· Soldering iron or some method of splicing.

Procedure (from Scott Mueller and Rob Cheek) :

1. Remove the black bezel surrounding the instrument cluster by removing the two bolts at the
top of it and pulling it back away from the dash. There are three clips at the bottom in the
back and two guide posts. Be careful with the rubber ring that goes around the steering
column as it is held on by some flimsy plastic rivets and cannot be reattached easily.
2. The tach will go in the right hand side of the black plastic in the bezel to avoid interference
with the turn signal and tilt levers and to allow the sacrifice of one of the two clips on the
right if need be (the left has but one). If you're careful, you can keep both of them. It will
need to rest on or near the point where the smooth grey plastic ends and the molded grey
plastic for the rest of the dash begins. Using the tabs and holes as a reference, find where the
center of the tach should be if it would rest about 1/8" above the lip and mark the spot on the
back of the bezel.

3. Using a 2" hole saw and starting from the back of the bezel, cut out the hole for the
tachometer. If you screw it up, don't worry: the bezel is only $15 and you can always try

4. Trial fit the tach. If it doesn't fit, work around the exterior of the hole with an Exacto knife
until it does. Don't cut too much: it should fit tightly.

5. Cut an identical 2" hole out of the grey plastic behind the bezel. You can re-insert the bezel
and use it as a guide. The tach will angle downward slightly, so take this into account.

6. Again, trial fit the tachometer. You may need to cut into the two slots for the clips. Make
sure the tach fits in below the clear instrument cover and does not bind. It'll be tight but it
will fit. Keep trimming the grey plastic until it does. Repeat ad-nauseum. You might need to
cut into one of the rectangular holes for the clips to make it fit.

7. Once it fits in well, make sure the wires are routed so that they'll dangle into the are below
the instrument panel and replace the bezel.

8. Remove the access panel below the steering wheel by removing the two screws on the
bottom of it. Then remove the steel plate behind it by removing the four bolts and pulling it
to the right. The wires for the tach should be dangling down there, or at least accessible from
there. Installing a four-way connector here would be a good idea in case you ever need to
remove the tach.

9. Tap in a "dimming" or "lights on" signal. The ashtray has both dimming lead and a ground
wire going to its light. The wires are also free enough to work with. The grey wire is the
dimming wire, and the black wire is the ground.

10. To get power to the tach, you might want to tap into one of the orange wires at the bottom of
the fuse box. Check the Helm's manuals for details: you want one that is only hot during run.

11. To get the actual tachometer lead hooked up, you need to route it through the firewall using
a factory, unused grommet. Look behind the LH wheelwell. There is an oval, rubber piece
there. Now remove the LH kickpanel and look near the point where the hood latch cable
exits. If you pull back the insulation, you'll see the same grommet. Use a sharp point to poke
a hole in the plug in the firewall, and then squeeze the 18 gauge wire through it. You might
have to fish it through using a coathanger or something.

12. The tachometer can take its signal from the black and white wire (negative) terminal at the
coil pack on the front of the LH cylinder head. Alternatively, another member has plugged
the lead into fourth, unused female terminal on the coil. The both go to the same spot.

13. Another good place to get a tach signal would be from the PCM connector pin A13. All B/Fcar
PCMs output the tach signal on this pin. You will need a terminal p/n 12084913 (for 20
ga. wire) to install in the PCM A connector (the factory uses a white wire for this

14. The wires should be inserted inside of factory ribbed conduit. You can cut a short length and
route to one of the factory conduits from the firewall grommet, or route a new conduit all the
way to the coil pack.

~Procedure by Scott Mueller & Rob Cheek

129 Posts
+1 what everyone else said (props for quoting the original Impala SS Technical Archives, Sarge).

But there is one gotcha with using the PCM connector A13. I've personally been tripped up by this. If you have an old vintage tach laying around, say one made before PCMs were common (one made in the mid-90s or earlier), it may not work from the PCM and will ONLY work when attached to the coil as described. Read the paperwork for the tach and make sure it can accept digital/transistorized tach signals.

The reason: most vintage tachs are designed to take advantage of the "coil collapse" spike (also called back-EMF, among other names). Since the PCM will only provide a square wave transistorized signal, older tachs cannot read that type of signal and will either function erratically or not at all. You can make an adapter using an old relay if you are good with electronics but why bother when you can 1) either buy a modern tach since they all work with PCMs nowadays, or 2) use the coil wire instead of the PCM wire.

How do I know all of this? A few years ago, I bought a vintage tach for one of my 9C1s. Why? Because I like the way the older ones look (fonts and colors are a closer match to our cars, warmer glow at night, etc). I like the way they work (non-digital). And they seem to sweep smoother IMO, not as jerky. Or some modern tachs that look acceptable cost $300. No thanks. So anyways, I tried to hook up the vintage tach to pin A13 and it didn't work.

(cue Derek's voice from Vice Grip Garage for dramatic effect)
Quite surprising when a guy spends an hour or two digging out the PCM wiring harness, making up a female pin connector for A13, running all of the wires, and fire it up for the first time... and nothing. A guy thinks he wired it wrong. Then a guy wonders if a guy got a bad vintage tach out of the box with a warranty that expired 30 years ago. I don't know. So a guy begins the troubleshooting.

I had a newer 4" Sun tach laying around that I use for quick diags on my cars. It worked fine attached to A13! So I dug out a spare relay, built this circuit, and then the vintage tach worked too... confirms my findings. I preferred to hook the tach to the PCM because I felt if a short happens somewhere by accident, the car won't stall. The PCM can handle a dead short on that pin (it has fault protection, it just lifts the signal going to the pin). Whereas if you short the coil wire, the engine stalls instantly and/or you can destroy the ICM.

Next time a guy wants to install a vintage tach on a car with a PCM or ECU, a guy should probably just run it straight to a coil wire.

Hope this helps.
  • Like
Reactions: Jimpala95

129 Posts
Excellent tip Storm9c1. The OP didn't say how old his tach was unfortunately.
Roger that. My thoughts were that these replies can be used as a tip for anyone searching for tach install problems in the future. Or if moderators want to pin it or move it to a more relevant place, that's fine too. Tach installation has definitely been discussed before. But I don't recall anybody mentioning the vintage tach issue.
  • Like
Reactions: Jimpala95
1 - 7 of 7 Posts