Project Lexus SC300 Road Racer: Part 7 – Sealing the Things


If you thought that your elementary school days of tracing were over, think again.

One easy way to make a panel for a hole is to press a piece of paper against the hole and trace it, then sketch around it slightly bigger to provide sufficient “lip” for a mounting area. This will become a mounting panel for a flanged bulkhead circular milspec connector and one flanged bulkhead Deutsch DT connector.

Why two different types? Cost savings and laziness.

Deutsch makes many types of connectors. In the motorsports world, the “high end” family is the “autosport” connector, for which there are several different lines/models. The next level down is the D* family of connectors (DT, DTM, and so forth). Both are sealed-type connectors, however the autosport type is circular and is a high-end aerospace grade component. It has a screw-on engagement with a threaded ring. Autosport connectors are also obscenely expensive, especially at higher pin counts.

Whatever your thoughts are on government or the defense industry, civilians like ourselves do occasionally derive benefit from them. In the case of motorsports, we have them to thank for the MIL-DTL-38999 standard. According to the encyclopedia of everything, there are a wide range of military specifications for connectors. However, the 38999 standard is the one that affects us, as it describes the “specification [covering] four series of miniature, high density, bayonet, threaded, or breech coupling, circular, environment resistant, electrical connectors using removable crimp or fixed hermetic solder contacts, and are capable of operation within a temperature range of -65C to +200C”.

  • Circular connectors provide for a high density of contacts in a small form factor.
  • The specification requires environmental resistance
  • A wide temperature range is desirable in our harsh motorsports environment

The other benefit to the use of MIL-DTL-38999 connectors is that they are standardized. This means that there are myriad manufacturers all competing to adhere to the standard for the lowest cost so that they can win contracts for their components to go in military equipment everywhere. While there are a few extremely high-end motorsports-focused connector manufacturers (Deutsch, mentioned above, included), they all have their own standards and are proprietary components. 

More people competing to produce the exact same quality of connector means we win. Big time, too, as using a Deutsch Autosport connector instead of a MIL-DTL-38999 connector can increase the cost by a lot. For a 26-pin connector it can be almost 400% more for the fancy black-and-red Deutsch Autosport unit! Remember that a circular connector has two halves. For just one 26-pin connection, this can be a cost difference of nearly $200.

After you get done buying the fancy black-and-red connector, you now need to go invest in a special tool to crimp the pins, except that the special tool to crimp the pins is such a fancy crimper that it has removable and interchangeable tool heads for the different sized pins. How fancy? Try $1,649 for the master kit with the crimper and all of the heads. Depending on your project, that can be more than the cost of all of the wiring supplies combined! Fortunately for us, MilSpecWiring, a division of MoTeC, has an interesting crimper option coming out shortly, and you'll learn more about that soon. Let's get back to the panels.

I already had a 12-pin DT flanged bulkhead connector shell on-hand, and this particular panel is going into the trunk area. Compared to the engine bay, the trunk is non-environmental. It’s not exposed to the same type of moisture, dirt, or fluids. So, for this use case, the DT connector will work. The DT connector is rated for 13 amps per pin. The fuel pump power, lights, and fuel level signal will go through this connector. We will be doubling-up on the number of pins used to carry the high current for the fuel pumps. As the pump might draw as much as 15 amps, and this exceeds the factory rating for a single pin, running two wires and two pins will effectively double our current carrying capacity. But you'll learn more about that in the future too.

The other connector on this panel will carry the two wheel speed sensor signals (right and left rear wheels) from the factory ABS sensors from the trunk back to the ECU. Since these are critical signals. I decided to spend the extra money on circular milspec connectors here.


The hand notcher is again used to get into the ballpark on the shape…
Followed by a pass or several through the belt sander to clean things up.
Small square holes are hard to cut, so a little time with some drill bits, files, and other tools makes quick work.

Since these are through-panel connectors, openings need to be cut in the panel to the appropriate size. MIL-DTL-38999 comes to the rescue again. Standardization means that every manufacturer's connector is identical, and the specification provides all dimensions, including mounting. It’s relatively trivial to download the PDFs and figure out what size openings to cut out. Deutsch also produces dimensional diagrams for all of the DT series connectors.

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