[DeTomaso] Seatbelt Light Problem

[MikeLDrew at aol.com]

In a message dated 3/27/07 20 28 19, spleen at spamcop.net writes:


> The red seat belt light in the middle of the dash stays on all of the
> time, even when the key is removed.  Has anyone else experienced this? 
> Any advice is appreciated.  Useful advice is *really* appreciated.
> 

>>>That light is actuated by two different switches.

The first is under the parking brake handle.   It is a pushbutton-style 
switch, the same as the one in each doorjamb that actuates the dome light.   When 
you raise the handle, the switch opens and the circuit is energized, turning on 
the light.

The other input to that light is from the shuttle valve (differential 
pressure valve) in the brake system.   There is a brass block underneath the brake 
master cylinder, with a bunch of brake lines going in and out.   There are two 
electrical switches there; the larger one actuates the brake lights, and the 
smaller one controls the red light on the dash.   If a brake hose bursts, when 
you step on the brake there will be resistance (pressure) on the intact side, 
while the compromised side will see reduced pressure (or no pressure).   That 
displaces a widget within the block, which depresses an internal plunger and 
actuates the switch.

So, to determine which of these two switches is malfunctioning, merely unplug 
one of them (the one under the brake master cylinder is easier).   If the 
light goes out, you have found your culprit.

As a matter of fact, if the light goes out under those circumstances (brake ci
rcuit), then you genuinely have a problem.   Even if your brake system is 
intact, it means that the valve fired at some point (it can be actuated during 
brake bleeding if it is done incautiously).   Although the valve isn't 
specifically intended to block fluid flow when it fires (hydraulic fuse), nevertheless 
it can have that effect, leading to squirrely braking, spongy pedal etc.

Given that your car has been sitting for five years, it is entirely possible 
that one or more brake calipers has suffered.   If you stomp on the brakes 
(while the car is stationary), it's possible that you might find brake fluid 
spooging out of one of the calipers.   So I'd investigate it very thoroughly.

Mike


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