On a 1989 420 SEL, after rolling about 10 yards, the ABS light comes and stays on, until the car is turned off. I thought it would be the front sensors so I changed both of them, but the light still comes on, after rolling about 10 yards.

I'm thinking it is a sensor since, the light is not on when the car is started, and it comes on after the car has moved about 10 yards. I can ride the brakes and the light comes on, or the car can move without any braking, and the light comes on. The OVP was changed about a year ago and no other warning lights are on. After starting the car, the light is off, I press on the brakes, and the light does not go on.

How can I determine what is wrong? Any ideas? Should I just replace the rear axle sender unit too?

Where can I get an abs testor? Are they expensive?

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1989 420 SEL