2000 Blazer 4WD switch panel LEDS blinking, TCCM relay clicking

Hi All
I am new to the forum. Good info here !

I have a 2000 LS 4x4 4.3 V6 90kmi with nearly all the typical problems.
Alternator replaced, Pitman arm replaced, just did the sweating oil lines myself, just had the inlet manifold gasket done by the dealer.
My last problem:
The LEDs on the 4WD switch panel are blinking (all together) and the relay in the TCCM is clicking. Every few seconds, but irregularly. The "Check 4WD" light also comes on often.
LEDs and "Check 4WD" light stay on only for a second or so. Sometimes I can feel the 4WD briefly engaging during this blinking, mainly on the highway at cruise speed.
I get the impression that the whole fenomenon is temperature dependent.
If I cool the TCCM down by switching on the airco, the problem seems to go away.
If I switch the heater on, the problem reoccurs.

I have driven a while with the leaking inlet gasket, so there is Dex-Cool all over the place under the truck.
There is also rain water coming through the blower inside the cabin. This water has been dripping on the TCCM wires, collecting in the TCCM connectors and caused some corrosion in both connectors (male and female sides). The TCCM electronics board look clean (it is protected against moisture by dipping in resin)
I cleaned all connectors as far as possible. To no avail.

When the LED's are not blinking, all 4WD modes seems to operate normally.

I have searched to forum but could not find similar problem description.

Any body any idea ?

Are there used TCCM's around ?
What is the best place to get a replacement ?
Kind Regards
John

Sounds like the heater core is leaking so do you smell dex cool (like a sour old maple syrup smell -close as I can come up with) in the cab and is your coolant slowly dropping - small holes often blow and reopen. No water should be getting thru the firewall or fan unless something is cracked. Also look at the 2 heater hoses at firewall and make sure they are not leaking and clamps on - sometimes after an intake job they forget a few details. As a test you can bypass the heater core by disconnecting the 2 hoses and putting a 5/8 to 3/4 " connector inline (all stores have these) and flush the core with plain water with a hose and see if the drip in the cab is there - but cover the distributor and don't get it all wet!
After that is fixed the TCCM may need to be replaced and ebay has a few of you match #s and as you may have seen online at rockauto or gmpartsdirect has good prices. There are sensors on the front right axle and transfer that feed the TCCM and check all vac hoses from intake to vac reservior, and down to actuator under the battery.

Thanks for the response Muddog321

The DexCool came from the leaking inlet manifold gasket and dripped down.
I was wonderring if that stuff corroded wiring or sensors.

There is no DexCool in the cabin.
It is rainwater that dripped on the TCCM and soaked my carpet.
If I put a hose on the windshield and the water flows down into the ventilation air intake, most of the water leaves under the truck.
But it starts leaking through into the cabin somewhere from the blower unit.
As far as I can see, around that big flap that is the air recirculation valve.

So, with no coolant in the cabin, the inlet manifold gasket just fixed and pressure tested, I don't think it is the heater core (maybe that will be the next one to go !! )

My best guess is still the TCCM itself, but before wasting the money on a new TCCM, I would still like to find out if someone else had the same failure and if replacement of the TCCM indeed fixed the problem.
Kind regards
John