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Will the Schroth Rallye 3 ASM Harness Fit My 1966 Ford Mustang Coupe?
Customer question: harnesses
A customer asked us: "I was looking at the Schroth Rallye 3 ASM harnesses. Are these universal, or do they come in different fits for different cars? I believe they are universal but just want to double-check. I wonder if you have any knowledge of the suitability of these for a 1966 Ford Mustang Coupe? If not, are there some specific criteria/measurements that would tell me if these would fit?"
It is a good question, because a harness is only as good as the points it is mounted to. Here is what the Rallye 3 ASM is, how it mounts, and what to check on a classic car like a 1966 Mustang before you order.
- The Rallye 3 ASM is Schroth's street legal 3 point harness, ECE and FMVSS approved
- It is not FIA homologated, so it is a road harness, not a competition one
- 2 inch (50 mm) webbing on the shoulder and lap belts
- Schroth's ASM system helps stop you sliding under the lap belt
- It has a quick disconnect tail strap, and it is handed, driver and passenger
- We hold no fitment data for a 1966 Mustang: the car's anchor points decide it

What is on this page
What the Rallye 3 ASM is
The Rallye 3 ASM is Schroth’s street legal 3 point harness, approved to ECE and FMVSS standards for road use. It is not a competition harness and does not carry FIA homologation, so it is for a road car that wants to hold the driver better than a standard lap and diagonal belt, not for a scrutineered class.
The shoulder and lap belts are 2 inch (50 mm) webbing. The three points are the two lap belt anchors and a single tail strap to the rear, and the tail strap has a quick disconnect, so it can be unclipped when you need the rear seat. ASM stands for anti submarining: an extra section sewn into the inboard shoulder belt that stretches at a different rate, which pushes your pelvis down into the seat in a hard stop instead of letting it slide under the lap belt.
Is it universal?
It is not made for one particular car, but it is not a one size fits every car item either. It comes handed, with separate driver and passenger versions, and it is designed to bolt to fixed anchor points. Whether it suits a given car depends on where that car’s anchor points are, not on the badge.
Schroth sell the Rallye 3 for cars that will not work with the 4 point Rallye 4, usually because the rear seat is too close to the front seats to get the shoulder strap geometry right. The tail strap should not angle down more than 45 degrees from horizontal; past that, the shoulder belts do not work as designed.
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What to check on a 1966 Mustang
We hold no fitment data for the Rallye 3 in a 1966 Mustang, so we would not tell anyone it fits without seeing the car. What decides it is the mounting points. Check that the car has sound lap belt anchors on both sides of each seat, and a strong point behind the seat for the tail strap, at a height that keeps the strap within that 45 degree limit.
On a car this age, look closely at the condition of the metal around any anchor. If there is no suitable point for the tail strap, a harness bar or roll cage gives you one.

Seats matter too. The standard seats can be used with a road harness, but a seat with harness slots holds the straps where they should be and is the better setup. Garreth’s advice for anyone fitting a harness to a classic is to send us photos of the anchor points and the seats before ordering, and to have the fitting checked by a professional garage. Our guide on how to fit a motorsport harness covers the angles and anchor points in more detail.
Is the Schroth Rallye 3 ASM universal?
It is not made for one specific car, but it is handed and bolts to fixed anchor points, so the car’s anchors decide whether it suits.
Is the Schroth Rallye 3 ASM road legal?
Yes. It is approved to ECE and FMVSS standards for road use. It is not FIA homologated.
Will the Rallye 3 ASM fit a 1966 Ford Mustang?
We hold no fitment data for that car. Check the lap belt anchors and a rear point for the tail strap, or send us photos.
What does ASM mean on a Schroth harness?
Anti submarining: a section of the shoulder belt that stops you sliding under the lap belt in a hard stop.
Why choose the Rallye 3 over the Rallye 4?
It suits cars where the rear seat is too close to get the 4 point’s shoulder strap geometry right.
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Our adviceCheck the anchors first
The Rallye 3 ASM suits a road car only when the car's mounting points are right for it.
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