Mercedes W123: boost and EGT gauges flush on the ashtray spot

Car

Mercedes-Benz W123, S123 (estate), C123 (coupé), 1976–1986, e.g. 200, 230E, 240D, 280E, 300D, 300D/300TD Turbo

Requires

the box of the free “W123 Mercedes Ashtray Replacement” (Printables 1584218, CC0), printed separately

Gauges

1 or 2 × 52 mm flush; “wide” variant with 59 mm spacing for wide front rings

Mounting

plate 149 × 69 mm, three legs with Ø 7 mm neodymium magnets on the bosses of the box

Gauge depth

box about 56 mm deep and open at the back; housings and connectors may stick out at the back

Fit

dimensions taken from the free ashtray replacement; our plate not tested in a car

Where the plate sits

The W123’s ashtray sits in the centre console below the radio. For this spot there is a freely published ashtray replacement (“W123 Mercedes Ashtray Replacement”, Printables 1584218, CC0): a box with a 150 × 70 mm opening and bosses for magnets, into which different plates are fitted. Our plate (149 × 69 mm) is one of those plates, just with one or two 52 mm gauges. Like the plates of the original project it holds with three legs and 7 mm magnets and can be pulled off at any time.

The gauges sit flush, held by crush ribs without screws. Nothing sticks out; the automatic selector gate below stays clear.

Which variant fits

• 1 × 52 mm – one gauge in the middle.
• 2 × 52 mm – two gauges, front rings up to Ø 58 mm.
• 2 × 52 mm “wide” – 59 mm spacing for wider front rings such as the Defi 52 (58.3 mm). The plate is the same size.

What the front rings of common gauges measure is in Gauge front ring sizes.

Cables and senders

Housings and connectors sit inside the box, which is about 56 mm deep and open at the back. The cables leave at the back, for example to the cigarette lighter wiring. Always use a fused power supply. On the turbo diesel, boost and exhaust gas temperature are typical; connect the boost line and the EGT probe following the gauge maker’s instructions.

Safety and controls

The plate sits flush in the centre console and does not stick out. According to our records the W123 was available with an airbag from 1982 as an option, in the steering wheel only; the centre console is not affected. Before driving, check that the plate is held firmly by the magnets.

What is tested and what isn’t

Our plate has not yet been tested in a W123. We took the box opening, bosses, magnet pockets and plate size from the free ashtray replacement (Printables 1584218, CC0) and checked them against its STL. Whether the box itself fits your car depends on the original project. If the plate binds, sand the edges lightly. The tolerance test ring shows whether your printer hits the 52.79 mm gauge bore.

Common mistakes

• Box not printed: without the box from Printables 1584218 the plate has nothing to hold on to – it does not fit the original ashtray.
• Magnets the wrong way round: before gluing, hold the leg and boss magnets together in their fitted orientation; they must attract.
• Defi rings in the standard variant: two Defi 52 gauges need the “wide” variant with 59 mm spacing.

Printing

The plate prints face down on the bed, so the visible side comes out smooth and no supports are needed. In the centre console PETG is enough, ASA or ABS also work, PLA does not (PETG or ASA in a car). You also need six Ø 7 mm neodymium magnets (up to 3 mm tall). The plate weighs 66 g and takes about 7 hours.

Fitting the gauge plate in a W123

1. Download the box of the “W123 Mercedes Ashtray Replacement” (Printables 1584218), print it and fit it in place of the ashtray.
2. Print the tolerance test ring in the final material and test-fit a gauge; then print the plate (face down on the bed).
3. Glue one 7 mm magnet into each of the three legs and each of the three bosses of the box; check the polarity first.
4. Press the gauges in from the front and route the cables out of the back of the box.
5. Fit the plate and check that it is held firmly by the magnets.

FAQ

Updated: 2 November 2026