The two manuals cited are still readily available on eBay, at reasonable price. I picked a set up a month ago for $40/shipped. They're both in good shape. And there were plenty of other manual sets, and single manuals, available at that time.
I have one of the aftermarket manuals (Haynes). It was better than nothing...but only just. Many things are either not addressed, or have a sentence or two, of a very general (and essentially useless for diagnostics purposes) nature, devoted to them. I paid $16 for the Haynes manual as I recall. I should have invested that money in the OEM manuals in the first place...
As pointed out by RalphP and others, all your acronym and location questions will be answered by these two documents, the "Ford Thunderbird Cougar Shop Manual", and the E&VTM...
Note that the following applies to my 89. I just went out and looked, and sure enough, it looks like I have one fan. Sounds like your car has two...? So not sure how applicable this will be to your situation. Still, hope it's of some help. Also, this information is offered freely and I make no claims to being a mechanic, or having any particular expertise in this arena. Use the information, suggestions, advice, at your own risk, according to your own knowledge and sensibilities. If you're not comfortable doing these types of diagnostics/procedures, leave it to a competent mechanic to do, so you don't get hurt (end of pseudo-lawyerly stuff...in a nutshell, don't blame me if you mess yourself, or your car up, following my advice. I am not an expert, and don't claim to be).
The following addresses the two main areas of potential failure, i.e., of the 'low speed fan' control signal (e.g., the LSFR/fan activation signal), and of the low-speed fan energize signal (fan motor power).
Referring to the E&VTM manual
it appears there's two fusible links (A and B) directly off the Starter Relay in a 12V line. The two are in series, with A also feeding the alternator. B is dedicated (and common) to both the coolant fan low and high speed relays. The low-speed fan relay (LSFR), located in the Integrated Relay Control Module (IRCM), feeds the fan motor in parallel with the feed from the High Speed Fan Relay (HSFR). Since the high speed relay's working (since the fan comes on during 'high speed' activation), it looks like the low speed relay, or its wiring between the IRCM and the fan motor, might be the issue. Most likely would be the relay. It appears the LSFR and HSFR are the same part number. If so, just swap them and see if the problem follows the relay...
The relays are energized (coil-side) by a signal from the Electronic Control Assembly (ECA). The LSFR signal comes from the ECA and into the IRCM on the T/O (Tan/Orange) wire. (The HSFR signal arrives on the PK (Pink) wire). Obviously, this 'activate' signal is critical to the operation of the relays/fan. If the T/O signal isn't getting there, it will be time to trouble-shoot the ECA circuit...but for now, I'm not going there.
It appears there's separate wires from the IRCM to the fan from both the LSFR and the HSFR. Internally (to the fan) the circuit from the relays is separate as well. Thus, it's conceivable you could have a fan that would operate for high-speed duty, but not low-speed (or vice versa). Check the fan low-speed circuit with 12VDC (vehicle's battery voltage) to validate operation, i.e., apply 12V at the BR/Y (Brown/Yellow) wire, with ground on the BK (Black) wire, both on the fan side of the plug. Note: BR/O (Brown/Orange) is the high speed circuit.
As for what sounds like frustration in your 'voice', I have gone thorough a litany of issues with my SC, too, since buying it, back in the Summer. However, after addressing each thing in turn, the general rate of failure has lessened. Until now, for the moment, I'm just driving it. My car sat for a while (year+), and wasn't driven. Besides being 24 years old (89), so there's a lot that simply 'deteriorates' due to the passage of time. Most of my issues have been 'electrical', i.e., sensors, modules, switches... I had the same experience (electrical 'gremlins/failures' on a 96 F250 I bought). I've owned the truck five years and now, and after replacing things as they failed during the truck's 'infancy' with me, it's become wholly reliable (took better part of a year to sort it out). I expect (or rather, hope...) the SC will be the same, ultimately.
Alan