76FJ55

Tom, for a quick test to see if the switch is working: roll down the windows then lock the doors to arm the alarm. now reach inside and pop the hood. if the switch is working the alarm should go off. if it doesn't then wht hood switch isn't getting a signol to the alarm either and could indicate a bad switch or at least there's possibly a common failure between the fan, light and alarm system.

Alan

if the light doesn't come on because of a problem with the switch - then the car thinks the hood is closed => fans should after-run.

Seems like you may have 2 isuues:

Fan after-running is mainly controlled by the intake plenum top thermal switch (test that - a simple switch - normally open (cold)) to simulate a hot intake short the 2 connectors together.

Your light may be disconnected in the hood loom - check that (common issue
if the hood has been off). Also check fuse 17

Alan

White Lightnin'

I too seem to have continuing issues with my hood switch. One of my mechanics figured out that the switch housing was loose and too low to provide consistent positive contact with the hood upon closure, and adjusted it accordingly. Simple and easy... but it seems to be acting up again.

My fans run for only about 2 seconds after shutting the engine off (I can hear them). That was the initial question to my mechanic (the fans). But, I also had the issue of the alarm going off at inconsistent intervals.

I also figured out an alternative solution for the alarm issue... open and close the hatch. Turning the key to the right not only opens the hatch, but turns the alarm off. Then simply close it -without turning the key to the left to activate the alarm. It looks odd to passersby... but effective.

I think replacement of the switch is the direction to take (at least in my case), with a modified bracket attachment (star washer; lock washer; loc-tite; etc.) to prevent movement and dislocation.

Tom in Austin

Interesting ... does the intake plenum top thermal switch have a function other than signaling a temp threshold has been met to the fan control system? Does fan control decide how long to run the fans after shutdown using the temp of the plenum, a stored map, other sensor inputs?

I know I've seen temp sensors mentioned in past posts, what is different about the location atop the plenum? Isn't there one on the coolant bridge that gives the LH the coolant temp?

White Lightnin'

Not sure of where the input is deciphered... but I have heard of many temp sensors in the NB models ('87-'95):

Top of intake plenum
Bottom front of radiator on driver's side
On automatic tranny
+more

I know if the plenum sensor contacts are bridged, the fans are supposed to run -if it is working correctly. This one is tied in with the hood switch...

Not sure of the other location inputs.

Alan

Thats all the plenum switch does.... though it also triggers full fans in run mode too - though usually if the pleneum is that hot the coolant will already be hot too ...

Note the alarm activation by the rear hatch varies with model year. For the new alarm module 91 & up the hatch works differently. When you open the hatch the alarm supends (without unlocking the doors) but when you close the hatch it auto resumes alarm functions. Earlier cars behave differently. The later module is also diagnostically enabled - so you can use a bosch hammer to read out the source of the last alarm activation trigger (handy)

Alan