Since I spend so much time prowling around car graveyards, I often find bits of interesting hardware that I must take home. Perhaps I will install those bits in a homemade boombox made from car parts, or save them for unspecified future projects. Sometimes I just want to admire a weird hoard of tiny pieces of automotive history. I'll make a 1980s Buick touchscreen computer work in my garage—someday—but for the past few years I've been struggling to make a factory-installed electronic compass function outside the discarded car from which I extracted it. This task proved much more difficult than I anticipated, but I finally pulled off the feat. Here's how it went.
Japanese car manufacturers spent the late 1970s and into the middle 1980s vying with one another for honor of having the most futuristic electronics installed in a new car. Nissan set a high bar with a voice-alert system that used tiny phonograph records to make Datsun 810s, Maximas, 200SXs, and 280ZXs speak, years before the competition used solid-state electronics to announce an ajar door. When the 300ZX appeared here for the 1984 model year, buyers could get an optional electronic dash compass that used an intergalactic-style green vacuum-fluorescent display to tell them their direction of travel.
Now that was major motion!
Since 300ZXs remain plentiful in the big U-Wrench yards, it's pretty easy to find one with the electronic compass still in the dash.
I learned from service manuals and wiring diagrams that the 300ZX's compass system had three components: the display that went into the dash, a brain-box under the dash, and a geomagnetic sensor that lives next to the sunroof. Just wire them up as the factory intended and you'll have a working electronic car compass! Sadly, after yanking compass hardware from several junkified 300ZXs, I never could get the thing to work right; later, I learned that most of these compasses failed well before our current century and that few 300ZX owners enjoy one that functions correctly.
Not to worry! Pontiac installed a slick-looking electronic compass in some high-trim-level Bonnevilles of the late 1980s and early 1990s, and these cars are even easier to find in junkyards than 300ZXs. I'd grab all the hardware I needed and have myself a genuine Bonneville compass telling me the location of magnetic north.
This task became even easier when a Midwestern 24 Hours of Lemons team obtained a Bonneville as an engine donor for a 1948 Plymouth race car and donated the circuit board from the instrument cluster to me at a race.
A quick trip to a local boneyard was all I needed to get the dash display and the trunk-mounted geomagnetic sensor. I bought a factory-issue 1993 Bonneville service manual on eBay and… was unable to get this rig to work. Disappointing.
Fortunately, I wasn't out of junkyard electronic compass options at this point (I don't consider Subaru's mirror-mounted compass to be sufficiently elaborate for my needs, as it merely shows a two-letter description of the car's heading). Mitsubishi, which makes all manner of consumer-electronics gadgets in addition to fighter jets, heavy-lift rockets, and sewing machines, went all-out providing cool gauges for the global-smash-hit Pajero truck. Known as the Montero (and, for a few years in the late 1980s, the Dodge Raider) in North America, Monteros could be equipped with inclinometers, thermometers, altimeters and—of course—compasses. Many 1992-1999 Monteros and Montero Sports came with space-age electronic compasses mounted atop the dash, so I broke out my junkyard toolbox and went shopping.
The compasses in these trucks live in a three-gauge cluster atop the dash. In the 1992-1995 Montero, the compass is on the left and the oil-pressure gauge and voltmeter are to its right. The 1996-1999 Montero Sport uses a similar cluster with a different compass design; I prefer the earlier version, so that's what I bought.
The geomagnetic sensor (which detects magnetic north), mounts on the dash between the gauge cluster and the windshield, so I bought that as well. Because this compass doubles as an outside ambient-temperature display, it requires the external temperature sensor to work properly. This may be found behind the bumper, on the left side.
Here's all the hardware you need to get a 1992-1995 Mitsubishi Pajero/Montero compass to work in your boombox, project car, whatever. From left to right in the photo above: compass display, geomagnetic sensor, ambient temperature sensor.
With help from members of some online Pajero/Montero enthusiast groups, I obtained wiring diagrams for the various flavors of Montero electronic compass and got to work sorting out the circuits on my junkyard hardware.
After a bit of trial and error, I was able to make my Montero compass function correctly when hooked up to 12 volts DC on the benchtop. Finally, after years of trying, a working junkyard electronic compass of my very own!
To calibrate the compass when it's in a Montero, you're supposed to drive the truck in a circle several times. After that, its brain retains its picture of the earth's magnetic field. All I had to do was walk in a circle while holding the battery-powered rig. The display looks beautiful in a certain 1990s-high-tech way.
I'll put this compass in my 1941 Plymouth project, eventually, and I feel certain that a junkyard boombox will get one as well. Just as a proof-of-concept, though, I decided to install it on the vehicle I've owned longer than any other: my mid-1980s Mongoose mountain bike that I bought in the early 1990s and used as a San Francisco commuter bike for years. I've got a more modern bicycle for around-town use, and the extremely battered Mongoose just gets used as a pit bike at local races.
I set a time limit of 90 minutes to get all the compass hardware installed and functioning on the Mongoose and got to work. First, some plumber's tape to attach the display unit to the handlebars. Plumber's tape is magical stuff.
I wasn't planning on riding this bike long distances in bad weather with the Montero compass in effect, so I wasn't too meticulous about the wiring.
The 12-volt battery pack (eight AA cells in a holder, very handy for junkyard use) went onto the rear rack with the help of some bungee cords.
The geomagnetic sensor gets confused by the proximity of too much ferrous metal, so I did exactly what NASA would have done to mount it away from the bike frame: found a couple of chopsticks and ziptied them to the handlebars, thus putting the sensor a few inches in front of the bike.
The ambient-temperature sensor went down low on one of the forks, so that I'd get a more accurate reading of ground temperatures while riding. After calibrating the compass by "driving the Montero in circles" (actually, just picking up the bike and spinning around slowly a few times), everything worked perfectly.
Ready for a test ride.
You can't really make it out in this sunset photograph, but the bike is facing 14,265-foot-tall Mount Evans, located nearly due west of Denver. The compass works perfectly… though you really don't need a compass in town here, because the mountains are always to the west.
Here's a stop at the '53 Ford F-100 I use for testing old cameras. I got some puzzled looks while riding around town with a funky-looking car compass on my handlebars, but that reaction couldn't dent my satisfaction over finally making a junkyard electronic compass work properly.
