Failed emissions test

it could be a loose wire or it could be the alternator is going bad.

Your vehicle is equipped with an OBD II computer AND a link to connect OBD II computer to a Smog Check Analyzer or Data Scan Tool (available
at most auto part stores).There are two types of codes, bad codes and good codes. The good codes are the "Readiness Flags". These Readiness Flags
indicate that certain emissions systems which the OBD II computer has been monitoring have PASSED the test, indicating that those systems are
working properly. Then there are the bad codes. The bad codes are actual "Trouble Code". These codes indicate that the OBD II computer
has detected a problem with in the emissions system. The Trouble Code will specifically indicate the component and problem which was found.
Newer vehicle's have very complex codes in the thousands.
"Readiness Flags" do not cause the "Check Engine" light to illuminate, but may cause a vehicle to fail the smog test.
In order to set all the proper "Readiness Flags" the OBDII system must complete at least one drive cycle (in some cases
two or three). A drive cycle is a sequence of internal tests which the OBDII computer runs while your vehicle is being driven. This insures
all emissions systems are functioning properly. Only then will your vehicle pass the smog inspection. A drive cycle usually requires one
week of driving.

Probably not a cheap fix.
The car will not pass the test if the light is on during the test.
The light is on when the computer has a problem that will affect emissions or performance.
You would need to have the computer scanned for trouble codes then fix the problem. Once the problem is fixed and the code is erased, the light should stay off.

It most likely is in a fail safe mode to protect it
from any damage

Usually that is exhaust converter damage, which is
govt emissions mandated

You should have a OBD2 MIL Lamp or some dash light lite

You address that problem, as you have all others & all
vehicles, for the last 30 years, since those systems have
been on all vehicles

You check for codes,then using factory trouble charts,
go to the system that the codes point to & then component
test

A cylinder misfire so severe it could damage the converter
is a common item & sometimes you get transmission
failsafes or overheating failsafes

take the ground line of the battery and press the brake for a few minutes and if the life is still on have the vehicle scann and clear code and have the emission components for the vehicle check

Rather then replacing a bunch of parts because someone suggested it could be this or that , your best bet , take it to a qualified diagnostic technician . One that has the knowledge an testing equipment . Could be any number of thing's . guessing doesn't work .
064 Emission Tests Scan Data Pre Check
003 Fuel System Tests Scan Data Tests

Go get your engine fixed at Jiffy...........You know they got a sale right???

Some vehicles require very specific drive cycles (called "drive traces" if you perform them on a road simulator or dyno) to activate certain self-checks like the catalyst and EVAP monitors. As a general rule, doing some stop-and-go driving around town at speeds up to about 30 mph followed by five to seven minutes of steady 55 mph highway speed driving will usually set most or all of the monitors. Consequently, if you're checking an OBD II system and discover that one or more of the monitors have not run, it may be necessary to test drive the vehicle to set the remaining monitors.

You should talk to a good emission tec, if this is not throwing a code, it is hard to say if that one of the components could be bad. O2,pump,convert, HeO2, every part of the emission system.

With a 1000 miles, and doing what is says above just before the test, and ending driving at the test
should be plenty. If it is not, you will have to have each emission part checked, or when the computer
is plugged in it might show a code that did not trip dash light.

Your vehicle’s computer system has self-testing capability. When the computer senses that there is a problem with some of the components it stores the correspondent trouble code(s) in its memory and lights up the "Check Engine" or "Service Engine Soon" light to tell you that there is a problem and you will need to have the car diagnosed and repaired.

Hate to be the bearer of bad news but mine failed at 29K and became undriveable at 31K and after years of hard handling, I treated that car like it was Christmas tree ornaments, fully expecting it to last until I am dead; the engine failed at 57,600. It's gone and I'm still breathing. It was the last GM anything I will ever own.