S2000 DIY Replacement Headlight Range Adjustment Sensor

6 Aug

Whilst replacing the drop links the other day on my S2000, I noticed that something wasn’t quite right:

This, as it turns out, is the Headlight range adjustment sensor (on the rear left, near, side suspension of the car), it controls the range of the HID lights based upon load on the rear axle don’t you know. Very clever, except mine had sheared right off, upon further inspection, the lower ball joint had seized solid and so it was only a matter of time before the rod snapped I guess.

I knew it needed replacing, and now that I knew what it was I started making enquiries, but the only few places I could get one wanted to sell be the whole unit including the electrics, for a tidy sum of course.

I removed the old unit and started to inspect it:

All I really needed was 2 new ball joins and the rod to connect them. Apparently the auto headlight level could cause my car to fail it’s MOT so leaving it off wasn’t really an option.

The diameter of the old rod was 6mm, this as it turns out is referred to a M6, metric 6. So I needed 2 * M6 ball joints and some threaded rod, well, not quite. The problem with this arrangement is that turning the rod would simply loosen one end as it tightened the other, making no adjustment to the headlights, fail.

Looking more carefully at the old rod, the thread at each end was going in opposite ways, which makes sense. The rod with the nut in the middle is called a linkage rod and is used for precisely this purpose. Now with the thread on the rod going different ways, the ball joints also need to be different, so I also needed one left hand (LH) M6 ball joint and one right hand (RH) M6 ball joint. I also needed 2 nuts, again, one LH and one RH.

Although you can buy M6 ball joints on ebay, I wanted the original part so I contacted Steve at Midland Engineering Services who got me a couple imported from Japan. This size ball joint is often used for the throttle linkage or motorcycle shifter linkage, so you may be able to try some of them, although bear in mind that it’s going to be exposed to the elements and needs to be fairly tough.

Fitting it was fairly straight forward, jack up the car, pop the wheel off and get to work. No real tips for this job other then make sure you can assemble to whole thing in the garage before going outside.

For reference, the original (and my replacement) rod was exactly 35mm from ball joint to ball joint.