Marshall electronic gauge install, Part 1

Discussion in 'Workshop Forum' started by Rodger, Jul 28, 2015.

  1. Rodger

    Rodger True Classic

    Location:
    Olympia, WA
    As part of my K20 swap, the instrument cluster needed to be modified to accommodate an electronic speedometer. Many thanks to Bob Brown for information and advice that he generously shared with me as I was attempting this. He was the one that developed the idea of using Marshall gauges to retrofit into the X1/9 gauge cluster, which makes for a nearly stock appearance. My understanding is that he has done well over a dozen of these, not only all of the gauge clusters for the in-house MWB K20 swaps, but has provided most if not all of the DIY ones. I have only seen pictures of Bob’s finished gauge clusters from the front, so what I am showing here is my effort only, with some advice from Bob.

    This is definitely a time consuming project, particularly the first time out, as there is a lot of trial and error cutting and fitting, as well as gluing and soldering. I got the Marshall speedometer and matching tachometer from Matt at MWB as he had a bunch in stock that he had acquired as part of his K20 swap service. For my K20 X, I had purchased a European cluster from a late model Bertone on eBay as I wanted an oil pressure gauge instead of the voltmeter.

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    Bob adds a digital voltmeter to his clusters, mounted in between the oil pressure gauge and the temperature gauge. I elected to not add this and will just rely on the alternator warning light, that replaces the low oil pressure light in the Euro clusters. The cluster I bought also has a fog light indicator in place of the seat belt warning light, a nice plus as I don’t need to be reminded to buckle my seat belt, but I do like having fog lights on my cars. I also found a rare genuine fog light switch that matches my other console rocker switches.

    The gauge cluster consists of three main parts: the faceplate that contains the front clear plastic cover and gauge bezels, the white plastic housing that holds the gauges and indicator lights, and the circuit board. The faceplate plastic and the black gauge bezel piece are connected together by 5 hollow rivets that I left connected as one piece. The cluster comes apart with four small black Phillips head screws. The circuit board is attached to the white housing by the various gauge mounting threaded studs as well as numerous white plastic studs that are “melted” to form like a nail head. These plastic heads are easily cut or snapped off. There are also the three socket housings that the wiring harness plugs into. They have the same type of melted nail heads accessed from the inside of the gauge cluster. Once the gauges are removed and the nail heads broken off, the circuit board comes off.

    This is a picture of the gauge cluster with the faceplate off.
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    This is a picture of the back of the Euro cluster showing the circuit board.
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    This is a picture I found on the forum that shows all of the connections for a US circuit board. The Euro one is a little different due to the oil pressure gauge.
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    Once the circuit board is separated from the white housing, the four diffuser domes for the backlight bulbs come out. Now the fun begins. I started by fitting the Marshall gauges to the black bezel openings of the faceplate. They actually fit quite nicely over the black rim of the bezel. Again, kudos to Bob Brown for figuring that part out. The gauges do not quite fit flush to the back of the faceplate but even though they have an aluminum rim around them, you really can’t see it from the front. I beveled the outside rim of the faceplate openings all the way around which allows the Marshall gauges to sit flush. The opening around the odometer reset knob also needs to be cut down flush to the faceplate. This all makes a lot of dust, but blasting through the gauge openings with compressed air gets all of the grinding dust out of the faceplate.

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    Even though the speedometer and tachometer fit nicely in the stock openings, there is still the opening for the odometer reset knob that is just an open hole. The Marshall speedometer has only one odometer display but it does have two trip odometers built into it that are activated and reset by a small push button switch. This push button is also used to calibrate the speedometer. This is to be mounted in a “convenient” location, according to the instructions. I decided to see if I could mount it into the hole for the odometer reset knob instead of somewhere else on the dash. I took the original odometer plastic reset knob from the Bertone cluster and cut it apart to get the middle section that was a cylinder.

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    This was partly hollow so I enlarged the center hole to accommodate the diameter of the red push button part of the switch. I then further enlarged the center hole on the end that would be against the faceplate to accommodate the threaded part of the switch body. I cut off the rim of the switch body that is used to mount it from the backside of a panel so that it would fit into the hole in the faceplate and my modified cylinder. I beveled the faceplate side of the cylinder so that it would be horizontal as the faceplate “glass” is at an angle. I then glued the body of the switch into the cylinder, then glued the cylinder and body of the switch to the faceplate. The wires coming from the back of the switch are then bent at 90 degree angles to clear the Marshall speedometer gauge rim in this area. Even so, I had to cut a notch in the aluminum rim so I could get it close to flush. If you don’t bevel the bezel openings, this step may not be necessary as the gauge will not be as close to the opening where the wires come through. Double check to make sure that the switch still works correctly at this point.

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    I elected to glue the gauges to the faceplate at this point. The alternative would be to glue them to the white housing once that has been cut to clear them. I am not sure how Bob did his. I used a clear strong adhesive cement (Loc-Tite, GO2 Gel) that remains slightly flexible as opposed to rigid epoxy in case I ever needed to get the gauges off in the future. This came in handy as after I had everything assembled, I found that the calibration switch was shorted closed and wouldn’t work. I was able to remove the speedometer, adjust the wires and that corrected the problem.

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    With the speedometer and tachometer securely in place, I cut openings in the white housing to clear the backs of them as they are self-contained units. Again, trial and error as I did not want to take any more away than necessary. Not only do you have to create the openings in the back, but also at the top and bottom of the housing where the gauge rims are to allow the white housing to seat all of the way. I also cut off the mounting screw studs off the back of the gauges as they are not needed. The Euro cluster has a blank indicator light where the US ones have the EGR light. At this point I swapped out the blank red lens above the temperature gauge for the EGR indicator light lens from my ’81. The Euro circuit board has the printed copper runs for this light, but there is no opening for the bulb since it is not used, so I created an opening in the circuit board to allow for an indicator bulb holder here. I also changed out the Bertone logo in the faceplate for the Fiat one from my '81 cluster.

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    The next step is to modify the circuit board, but it is late so that will be in Part 2.
     
  2. Pete Whitstone

    Pete Whitstone True Classic

    Location:
    McKinney, TX
    Fantastic work!

    I love what you did with the speedo reset/calibration button. Mine is down in the cubby forward of the shifter, but I'd much rather have your installation. Gives me a guide to work from if/when I ever tear it all apart. Thanks!

    Pete
     
  3. Rodger

    Rodger True Classic

    Location:
    Olympia, WA
    Part 2

    The next part of the project was to cut openings in the circuit board to clear the gauges. Again, lots of dust. Obviously, this removes several of the printed runs on the board as well as half of the connector spades for the 8 pin connector. The red 6 pin connector can be accommodated with a small amount of cutting of one corner of that housing. Once I had the gauge openings created, I worked on figuring out the backlighting of the gauges. The Marshall gauges are self-contained and have their own LED internal lighting, but the oil pressure, temperature, and fuel gauges still need to be backlit. This probably took the most time as every time I would try something, I would need to assemble the cluster, attach power to the board and the Marshall gauges and see how it looked. The Marshall gauges need connections to ground as well as three different 12v power connections. Direct from the battery, 12v from the accessory side of the ignition switch, and 12v from the backlight circuit. There are two colors of LED backlighting in the Marshall gauges, white and amber, so I chose white to match my other backlight LEDs.

    Three of the four of the stock backlight sockets openings are destroyed with the modifications for the gauges. I first tried using the one remaining stock opening above the oil pressure gauge with an LED replacement bulb. I then “moved” the opening for the one above the temperature gauge and epoxied in one of the stock backlight bulb holders and soldered a jumper to the circuit board for power. Again, I put an LED in this socket.

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    Since I had successfully created the opening for the small bulb holder for the EGR light, I created a similar opening in the circuit board, above and to the right (from the front) of the fuel gauge and put a small LED in that holder.

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    I did a trial assembly of the cluster to see how it would look. Definitely an improvement over stock, but not anywhere near as bright as the Marshall gauges.

    Bob Brown had told me that he used a single small LED mounted in between the oil pressure and temperature gauges, and one mounted above the fuel gauge, epoxied to the turn signal indicator light housing. In my rummaging for small gauge wire to attach the additional LEDs to, I came across an old circuit board power socket and wire from a computer. I bent the leads from the LED bulb straight and it fit nicely in the socket. I then epoxied that holder to the white housing between the oil pressure and temperature gauges.

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    I couldn’t find another one of those sockets in my junk pile, so I just soldered some wire to another LED bulb and epoxied the wires to the housing to mount a bulb above and to the left of the fuel gauge. I extended the leads on the right side LED to move it closer to the fuel gauge, so now I had two LEDs on that one, and the center LED and the two original position backlights for the oil and temperature gauges.

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    Again, reassemble, test. This time the brightness was pretty good, but I was getting too much direct light from the LEDs above the fuel gauge shining down onto where the lower rim of the instrument pod would be. I went back to the original LED in the socket to the right of the fuel gauge then cut part of the base off of another one and epoxied that one on the left side about the same height, which kept good brightness, but reduced the glare effect. Unfortunately, I forgot to take a picture of those bulbs in place. Anyway, here’s how it looks with all of the backlighting powered.

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    While figuring out the backlight issues I soldered several jumpers on the circuit board to fix all of the cut connectors and to get power to the Marshall gauges and the various indicator lights. The Marshall gauges need a ground, +12v from the accessory position of the ignition switch, +12v from the backlight circuit, and the signals from the engine to the tach and transmission to the speedometer. The power and ground leads are soldered to the board. The signal wires as well as a constant +12v from the battery will be added to the wiring harness.

    To recreate the 8 pin connector, I used the four left side (from the back) spades that were still attached to the board and used them to substitute for the original right side spades. I cut about a 2 mm gap in their original runs and then soldered jumpers from them to the runs that belonged to the original right side spades. Make sense? In my ’81, the original interior was really sunbaked from 30 years of California sun so the turn signal/windshield wiper switch was pretty oxidized and will be replaced with a new one. This switch happens to have an 8 pin male connector that matches the one on the wiring harness so I used that as my new 8 pin connector for the instrument cluster. I crimped on spade connectors to the right side wires and just plugged them to the circuit board and then soldered the left wires to the appropriate runs. There is one pin that is the tachometer signal so I crimped on a spade connector to that wire and plugged it into the Marshall tachometer. Here are a couple of pictures of some of the jumper connections, but until you actually get in and trace where all of the runs go, it is kind of hard to follow.

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    There is also a difference in the signal to the seat belt light vs. the fog light indicator. This is seen in a difference between where the jumper wire on the stock tachometer is connected on a US cluster and a Euro one. The US jumper goes from the 12 volt terminal on the tachometer to the indicator light and uses a ground signal from the seat belt circuit to light it up. On the Euro cluster, the jumper is connected to the ground terminal on the tachometer and uses a positive signal from the fog light switch, just like the other indicator lights underneath it. I just cut the jumper from the fog light circuit and soldered it to the ground path of the other lights.

    I found that the additional LED bulbs to light the gauges create some light bleeding onto some of the indicator lights and the turn signal indicator, so I used some black sticky weather stripping material to create a light dam to prevent this. I also found that on the back side of the black faceplate, there is a lip next to the opening for the temperature gauge that extends farther out than the one on the oil pressure gauge side. This created a shadow on the temperature gauge so I trimmed about half of it off and that made it about the same as the oil pressure gauge. I also added some white paint to the back of the faceplate in the area of those gauges to get better reflection of the backlight.

    I then double checked to make sure there is no dust anywhere, then assembled everything with the four Phillips screws. The oil pressure, temperature, and fuel gauges hold the circuit board nicely to the white housing but I added some epoxy to some of the original plastic studs to help keep it solid. Glue on the red and white 6 pin connector housings, solder the ground wire of the calibration push button to a ground run, and plug in the spade connectors to the appropriate spots on the Marshall gauges. It is pretty cool when you apply power to see the gauges light up and the Marshall gauge needles swing all the way clockwise, then back to zero, just like a modern car. In TonyK’s recent video post of his Abarth swap, there was a section where you can see the Marshall gauges peg over upon start up.

    The last thing I did was to use more of the black weather stripping to seal the gaps around where the Marshall gauges protrude out of the circuit board to prevent dust from getting into the gauge cluster. This should also help to support the back end of the gauges without permanently gluing them in. I wanted to have a way to get back into the gauge cluster in the future, should I need to fix something or change one of the LEDs out. Here are some pictures of the final backside and one of the front.

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    After working on this in my spare time for the past couple of months, I can really appreciate the time it takes for Bob to assemble one of his custom gauge clusters. Again, thanks, Bob for your advice on this.
     
  4. jvandyke

    jvandyke True Classic

    Location:
    West Michigan
    :worship:
     
  5. fiatmonkey

    fiatmonkey Tim Hoover

    Location:
    Redwood City, CA
    I appreciated Bob's efforts so much...

    I asked him to make mine :laugh: I got lucky and he had one ready to go!

    I didn't include the trip button, but I am considering adding it in.


    Looks great Rodger!
     
  6. Henway

    Henway True Classic

    Location:
    San Diego, CA, USA
    At this point, maybe it would make more sense to make your own PCB and etch it? Seems like it would be less work and better quality if you're making more than 1....
     
  7. Rodger

    Rodger True Classic

    Location:
    Olympia, WA
    Nice idea

    If I were going to go into business doing these, that could make sense, but this is a one off for me. There is very little room to go around the Marshall gauge housings so I doubt if you could do printed runs and keep them the same size as the stock ones. Of course, if you use all LEDs, then the current requirement would be much lower than the incandescents. Another idea would be to have sockets on either side of the gauges with ribbon cable jumpers to go around them like in a computer. I'll leave it to someone else to try. My K20 to do list is so long at this point. :sigh:
     
  8. Rodger

    Rodger True Classic

    Location:
    Olympia, WA
    Good move

    Having Bob do it was definitely the smart thing to do and his quality and experience is first class. I thought it would be a "fun" project and it was in a strange sort of way, but that's me. :wacko:
     
  9. bbrown

    bbrown Bob Brown Moderator

    Location:
    New Hampshire
    Nice Job Rodger

    I also thought it was a nice touch to add the switch to fill the reset hole. Dual function. I never thought of doing that. Great job!
    There were a couple discoveries you made like painting the reflective surface white on the back of the faceplate for light reflection and your use if the 8-pin connector. (I use the pins and the connector housing from the PCB and made up my own. Takes a while to do though)
    I'm sure you've learned a lot doing this project. Imagine doing a dozen more just like it! :grin:
    Anyway, nice job Roger. Thanks for sharing.
     
  10. Yves

    Yves True Classic

    Roger,
    I can appreciate all the work you have done in that project, I made similar project but with a Fiat Punto

    Great job:worship:
     
  11. Rodger

    Rodger True Classic

    Location:
    Olympia, WA
    Yours was great

    Hi Yves,
    I saw your thread on the build of your gauge cluster and read through it as part of my initial research. You do exquisite work and it was a beautiful result.
     
  12. Tas

    Tas Rick Di Giulio

    Great job Rodger I also had Bob Brown do my cluster that's works vary well Thanks Bob
     

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