The gauges when I purchased the car. BTW, while I don’t have documentation to support it, the cars mechanical condition makes me believe that is the actual mileage.
This week, I’m going to review changes I’ve made to the El Kylemino’s gauge package. This image shows the original gauge package. It included the base speedometer and fuel gauges plus an optional trip odometer and additional gauges measuring temperature, oil pressure, and system voltage. A factory tachometer was offered, but not installed on my truck. Instead, a blanking plate resided in the tach opening.
At the time of purchase, I had the following mechanical issues with the gauges:
- The fuel gauge always remained below 1/3 full.
- The voltmeter always pointed to the 10 O’clock position.
- The temp gauge always pointed to the 2 O’clock position.
- Time had gummed up the trip odometer reset, and the knob was missing.
I also had the following appearance/performance issues with the working gauges:
- The tach opening used a blanking plate.
- At night, the gauge back lights were too dim.
- The gauge opening consisted of boring black plastic.
- And finally, the speedometer only went to 85 MPH.
I’ll review each step in detail, but I fixed the mechanical issues with a bit of lubrication and a few spare parts, and improved the appearance issues with some E-Bay hunting and a little creative effort.
Modular gauge design- The light blue plastic carrier supports four gauges, which then plug into the gauge base.
Before we cover all the work, let’s look at the gauge assembly design. It uses modular gauges, meaning each element plugs into a separate instrument panel socket.
Modern gauge assembly- NOT modular
In contrast, modern gauges use a single soldered circuit board, making repairs more difficult. Thanks to modular design, I was able to disassemble the cluster and fix or install parts as needed.
Typical GM Gauge Shunt
To repair one bad gauges, I installed a spare shunt I had laying around. Most modular GM included a shunt as a calibration device. While it appears to insulate the terminals from the gauge case, it is actually a resistor.
This schematic shows the basic circuit. Changing the shunt resistance modifies the gauge reading. This design allowed GM to use the same internals in different gauge cases and could fine tune each gauge to match different vehicle circuits.
The back of the gauge assembly. I laid resistors over the bad shunts, restoring gauge operation.
To check a shunt, measure the resistance. A reading around 75 ohms ohms indicates a good part, while an open circuit indicates a problem. Three of mine were bad and I only had one spare shunt, No problem- On the other two gauges I installed the correct size resistor between the terminals, as shown here.
Typical odometer with a trip option
With new resistors installed and the gauges working, I moved on to the trip odometer. To free up the mechanism, I cleaned it with contact cleaner, and followed up with some silicon spray lube. These type of solvents can remove paint, but I got lucky and restored smooth reset operation without damaging the numbers.
With all gauges working, it was time to fix the appearance and performance issues, I did some research and bought the following items:
- LED bulbs designed to replace the 194 bulbs used in the gauge assembly ($ 15)
- A tach designed for a V-8 El Camino or Monte Carlo ($ 65)
- Chrome dress-up trim rings ($ 40)
- A new trip odometer knob ($ 12)
- A 115 MPH speedometer from a late production Monte Carlo SS ($ 75)
E-Bay LED Dash Lights- I recommend them!
I’m covering the LED bulbs first, since I’m EXTREMELY pleased with their performance. After about six months, they’ve proven to be both bright and reliable. In fact, I never use the full brightness setting during normal driving. Amazon also sold them to me for peanuts, making them the best deal here.
The red 1/4 circle shows where my dash lights drop out (go dark)
I do have one minor complaint- When I dim the gauges, the LEDs “drop out” and go dark at about 60% brightness (a characteristic of these bulbs). Ideally, they would work over a wider range, so I’d have dimmer dash lights when driving on pitch black highways. However, I rarely drive in that situation, and have a plan to improve the dimmer performance. If the plan works out, I’ll fill you in on the details.
My bulbs did not have a plus mark, but all LED bulbs are polarized
I also discovered an installation issue. By nature, LED bulbs are polarized, meaning the bulb has a hot terminal and a ground terminal. The 194 bulb is not polarized, so the bulb and mounting socket lack guide pins or other mechanism to properly position the polarized LED.
Typical instrument panel bulb sockets. Like the bulb, the sockets are not polarized.
Therefore, the odds are exactly 50-50 that you’ll put the bulb in backwards. I was able to pull the gauge assembly out of the car and power lighting circuit during bulb installation. If a bulb didn’t light, I simply turned it 180 degrees, restoring polarity. The LED bulb directions do NOT make this clear, so keep polarity in mind if you ever change out incandescent dash bulbs for LEDs.
While looking for gauge parts on E-Bay, I discovered two things. One, late model El Caminos and Monte Carlos used unique gauge fonts and markings, so I couldn’t use parts from the earlier cars.
A typical Monte Carlo SS speedometer on E-Bay
Two, Chevy used a 115 MPH speedometer in the Monte Carlo SS during the last two years of production, and I decided I wanted one. In fairly short order I found a tach and a speedometer, and they ALMOST bolted right in.
This added resistor re-calibrate the tach for a V-6 signal
Because I purchased a V-8 tach, it needed to be re-calibrated. To do this, I increased the resistance in one tach circuit by cutting into the circuit board path and soldering in a resistor. I thought I might have to try a couple different resistor values, but I nailed it on the first try. Using my scan tool, I compared the RPMs in the data list to the tach, and they matched right up.
Typical factory wiring and an actual V-6 tach- Notice the lower red line.
To install the tach, I had to add one wire from the distributor to the gauge cluster – The tach mounting bolts connect it to the gauge circuit board, which provides it with power and ground.
This is how you remove GM dash connector terminals. For more information, see Ray’s Chevy Restoration Site
To complete the signal circuit, I just had to plug a terminal into the connector cavity and route it to the signal side of the coil. I salvaged a couple of terminals with the factory crimps from a junkyard Chevy, and included a signal filter (scavenged out of a ’84 Corvette) in the circuit.
Here’s how to remove a speedometer needle with a fork- Thanks Google Images!
On the speedometer side, the (used) part arrived with a broken trip odometer. To fix this issue, I used a fork to pop off the needle, removed the face plate, and swapped in the odometer assembly from my old speedometer (and installed the new knob). This fixed the trip odometer, and the replacement speedometer mileage now exactly matched the actual vehicle mileage.
During my E-bay search, I also discovered this set of six trim rings that mount on the shadow box, dressing up the (extremely) plain gauge face. After placing an order, I used a two part epoxy to install the rings, and glued them in while I had the gauge assembly apart.
Done- 115 MPH speedometer, working gauges, added tach, and bright trim rings!
Which brings us up to date, and ready to look at the complete project package. For less than $200, I was able to restore all functions, add a tach, improve the speedometer, and add a bit of flash behind the lens. Even better, I can now SEE the gauges during night time driving. Mission Accomplished!
Until next time, D/S
Articles such as this are what keeps me coming back to this site day after day. Fantastic write-up.
Awesome! Love reading this stuff. And I’m still very green when it comes to knowing proper resistance in a circuit and how to fix. AND good to know the part about the polarity of LED dash bulbs vs. regular ol’ 194s.
Yep! The “D” in LED stands for diode. This can be frustrating and useful at the same time as it can indicate an improperly installed circuit with reverse polarity.
“I’m still very green when it comes to knowing proper resistance in a circuit and how to fix.”
As was I back in the day, but over time I’ve acquired knowledge, mostly through direct experience. I try to keep out of the weeds on electrical, instead touching on the high points and maybe sharing the basic circuit schematic. But if there’s a point you want clarification on, feel free to ask.
I’d also encourage you to keep digging into volts, amps and ohms- I now make my living teaching technicians automotive electrical theory, which is far preferable to to earning my daily bread by working in a shop.
There are few things as satisfying as restoring dash functions. After all, this is the thing you look at the most when driving your car. Burned-out dash lights were always one of the first things I would fix when buying an old car.
Dash lights were always one thing I found wanting in the GM cars I drove. Ford and Chrysler designs always seemed 1) a little brighter and 2) a more pleasing color, more green or blue. Knowing the appeal of GM’s grayish-white dash lighting I can understand your desire to move to LEDs.
I was waiting for some method to alter the redline on your new tach to match the V6’s upper limit. Or yellowline, in this case. I am surprised someone has not come up with a decal for this. But I guess those of us who get stuck in the details have to strop somewhere. 🙂
Several years ago white face gauges were all the rage, they were a simple sticker to overlay the factory gauges. They certainly could put the redline anywhere they wanted. Heck there were even white face kits for my Internationals.
Scoutdude-
There’s still a kit available, which offers 3 overlays for the speedometer (85 MPH without trip, 85 MPH with, and 115 MPH deluxe) the 4 center gauge overlays, the 3 center idiot light overlays, the tach blanking plate, the analog clock face, a blank PRNDL overlay (for console shifters), a 4 speed overdrive PRNDL overlay and….
One tach overlay with the V-8 redline (no V-6 overlay).
My 4.3 just doesn’t get any respect….
If I need to replace any bulbs in the dash of my G body, I’ll use these.
The Sylvania LEDs while expensive are much better in my opinion than the cheap ones found on e-bay and Amazon. My recently acquired Marauder came with cheap LEDs in the dome, reading and foot well lights. They were a harsh color and when the car did the fade to off with the interior lights they flickered anoyingly. So one of the first things I did was to replace the dome and reading lights with good old Incandescent. However for the foot well lights I went with the blue Sylvania units, since the car is blue. They do not flicker as they fade away and do go farther on the dimming scale before they quit.
So yeah I highly recommend that if you are going the LED route to spend the extra money on the name brand bulbs.
Nice work. One nice thing about the Fords from this era is the tachs are universal. When I replaced the 4cyl in my Foxstang with a V8 all that was required was pulling off the cover and using a small screw driver to move the switch from 4cyl past 6cyl and to 8cyl.
When the tach started acting up in our Tempaz I also found out that Ford had prepared for a V6 in them well before they actually offered it, as the middle of the run cars had tachs with 4 and 6cyl settings.
I wonder if the Taurus-Sable (or even the Ranger) used the same tach…
Speaking of GM G-bodys and the related platforms (like the El Camino) there was an article in Hot Rod many years ago detailing how to take the Canadian market speedometer with its kph reading and make it read mph on the much numerically higher kph numbers – that was one way around the “only reads to 85 mph” restriction.
Just an FYI.
I prefer originality, but those chrome rings really take the “cheap” out of that cluster. The first thing that came to mind was that it reminded me of the beautiful 1967 Chevrolet “B” body dash cluster.
I never knew GM made a V6 tachometer like this and thought the option was only available on V8-equipped cars. Nice writeup.
You could give me a month of Sundays and I’d never be able to accomplish this task. But I know good work when I see it. What a great project and write-up!
Lots of fiddly work but it must be very satisfying when it all comes together and works. I understand LEDs have some very strange characteristics – on my 64 Comet they were very useful in getting serious candlepower for the interior lights but are useless as instrument lighting (no stronger than the original, cannot be dimmed) and I have no idea why. As I’m not doing too much night driving I’m not that bothered but.
I love reading this article. If only I could do this kind of work to my El Camino. I can change out the dash bulbs, but not much more than that. Wonder if there is someone in the Augusta, GA that does this ?
I’m about to do something very similar to my Ford Ranger.
I miss the days when factory options like a tach or other, additional gauges were simply plug-and-play, and no changes to software are needed.
If I can hack the software and just turn on the features, that’s a preferable option. But even modern systems often need a hardware change out to add gauge features.
I’m expecting everyone to eventually embrace the Tesla approach (visual display screens for all dash images), but it looks like it may be a long wait…
Great work Dave. I am just catching up on CC articles and this series is great. I can’t believe how much better those chrome rings improve the look of the cluster. I am looking forward to further installments.
Excellent tech article, could you add the resistor values in case someone else needs the?
Let me say this about resistor values up front:
First, tweaking the tach display by changing resistors only works for analog gauges with discrete components soldered to a board. If the tach displays actual RPM, or uses a tiny integrated chip board to drive the needle, you’ll need to convert the tach signal using an external box. These boxes exist, but cost from 85 to 150 bucks…
Second, I have no idea how many different years and models of GM tachs you can modify using the resistor I used, but I’m guessing there is NOT a one resistor value solution.
OK- Here’s what I recall about the resistor value:
I calculated the correct resistor value by measuring the V-8 resistance, and then multiplying that value by .75 (6 divided by 8). The basics are covered in this link, and suggests you use a variable resistor to fine tune the tach (something I did not do).
Thanks, D/S
Tach modification link