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.
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.
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.
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.
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.
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)
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.
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.
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.
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.
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.
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.
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.
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.
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.
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