No Radiator Far - Why??

[Al Powell]

Friends, I'm stuck with an electrical problem.  Allow me to tell the story
and ask for help...

Recently, my wife's 1990 200 overheated and dumped its water.  The
immediately evident problem was that radiator outlet on the bottom of the
coolant expansion tank broke off....releasing the water. So I replaced the
burp tank, re-filled system, fired it up and then spotted a pinhole leak at
the top forward corner of the radiator.  Bad luck, but not dreadful.  I
pulled the radiator and took it to a good local shop, got it fixed.

Re-installed radiator.  Re-filled system with water, fired it up, let it
idle until full operating temperature - and more - was reached.  But the
radiator fan does NOT turn on.

I checked the three wires in the connector going to the thermoswitch mounted
on the radiator.  One of them had 12 volts with the key on, but none of the
three leads had power with the key off (logic says that one should have had
power, since the fan can engage with the key off).  I tried jumpering all
possible combinations of the leads but got no fan engagement.  According to
the Bentley, this means a break in the leads (jumpering them is suposed to
engage the fan), although the ONLY diagnostic procedure shown in the Bentley
is for the 20-valve model and I have the 10-valve turbo...so whether the
Bentley comment applies to the 10-valve at all is highly questionable.
(Also, the terminology in the Bentley implies that there are only two leads
to its thermoswitch, and I have three leads to mine.)

I checked fuses, found no fuse attributed to the main fan, and I checked the
fusible link for the fan - it's OK.

So - I pulled the radiator back out and replaced the thermoswitch, on the
assumption that the thermoswitch must have gone out or been damaged when the
radiator guys worked on it.  (If you ever want to do this with the radiator
in the car, you will need a 29MM deep-well socket, as a standard depth 29MM
will not reach pst the electrical connections; otherwise there is NO room to
turn a wrench.  I didn't have a deep well, so out it came).

Re-installed the radiator, secured all connections, filled with water,
started it up and got it hot - and still no radiator fan.
*$#^@)#^&#????????

Re-checked the wires running to the thermoswitch.  No power to ANY of the
wires, whether key is on or off.  What the ^&%##^&%???  I checked the relays
and found that on the fuse block under the hood, relays for "Radiator
coolant fan" and "Radiator coolant fan 2nd stage) are identical relays next
to each other.  Figureing thta one might be bad but probably not both, I
swapped the relays.  No change.  No power in any lead going to the
thermoswitch, regradless of whether the key is on or off.

Where the heck do I go next????  To the 2-stage fan relay?  And am I not
correct that there should be power to one lead on the thermoswitch with the
key off??

I'm stumped to figure out where the electrical circuit going to that
thermoswitch could be broken.  I see no fuse connected to that circuit other
than the fusible link in the main lead to the fan, and it's still intact.
Swapping the first two stage relays made no difference.  The third stage fan
relay is in the under-dash panel which is a PITA to get at, so i've left it
alone.  Stage 3 fan function is not the issue, anyway.  I have pulled EVERY
fuse in the under-hood fuse block and they are all good.

Any BTDTs?  Anyone with good ideas?  Is the damn fan wired thru the license
plate light or the cigarette lighter, or some other bizarre place to check?
The car will be sitting until I get this figured out, and I need it on the
26th.

Direct replies to this email address would be appreciated.
<powellae at home.com>

Thanks in advance.  This one is weird!
++++++++++++++++++++++++++++++++++++
Al Powell
Fort Collins, CO
'58 Fiat 1200 Spyder "Transformabile"
'83 Datsun 280ZXT
'90 Audi 200
'93 F-150 4X4
++++++++++++++++++++++++++++++++++++