Yes this is true but only for 1984 and older Vanagons. The 1985 and
newer models did away with the single circuit hydraulic failure sensing.
The 2 switches are still on the master cylinder but they only serve to
trigger the rear brake lights. The warning logic is contained in the
module on the left side of the dash as part of the brake/seat belt
indicator. The logic modules are different.

Mark

>
> Look for the ground points up behind the fuse/relay assembly.
>
> There are pressure switches (two I believe) attached at the master
> cylinder.  They sometimes go bad.  If you disconnect the wires from them
> and check with an ohmmeter, you should see a big change in resistance (
> infinite to nearly zero) when you press on the brake pedal.
>   I believe that the electronic logic, where ever it may be, turns on
> the warning light if it senses pressure in the front brake circuit and
> not the rear or vise-versa.
>
>  Larry A.