I can't find the photo on the forum of the 1990 fuse box, but it goes like this:
top row, from left to right: right headlight (10a) left headlight (10a), tail/dome (15a), stop/horn (15a), hazard (15a), cigar/radio (20a), spare, I believe (25a).
bottom row from left to right: ig-coil meter (15a), turn/back (10a), wiper/washer (15a), rear defroster (15a), heater (25a), door lock (20a), diagnostic fuse.
So the dome fuse is on the top row, 3rd from the left.
By the way, the tranny and transfer case use GL-4 (safe for yellow metal), the diffs use GL-5.
When you are reading info on the forum, there is some confusion about IAC vs ISC - Suzuki changed these abbreviations at some point. Normally the ISC is the electric solenoid - on the 1990 it is totally electric. The ISC for your car is expensive, and may be pretty hard to find. The purpose of this is to regulate the idle under load. The IAC, at least on the forum, is normally thought of as the mechanical wax pellet valve that is on the passenger side of the front of the throttle body, behind a metal plate. If you remove the metal plate, you will see an air port on the right side - this port provides additional air at cold start, and as the car heats up, the wax pellet expands to move the valve forward to block this port up. The IAC is only functional at cold start, and unless there is a problem with it, it does nothing once the car is warmed up.
Your cold start sounds fairly normal, with the exception of the 1000 rpm warm idle. This can be caused by a vacuum leak - you can check for leaks by pinching your vacuum hoses with a pliers - you should not get a change in idle on any hose that you pinch - if you do, then either the hose, connection, gasket, etc., is leaking on that circuit. Frankly, unless you find a definite leak, I wouldn't be tremendously concerned about a slightly high idle. However, you advise that with the headlights on, your idle rises and you hear a clicking - this is most probably the ISC solenoid. If you stand on the passenger side of the engine, it will be pretty much in front of you - easily identifiable if it is clicking away like mad. If you disconnect and remove the solenoid, you can hook it up to 12vdc (a poster here actually got it to work with a little 9v battery) and watch it work - there is a little plunger inside that vibrates at something like 20x a second - this plunger can stick, etc., especially after years of service. You can get carb cleaner and carefully clean the solenoid so that the plunger is free to vibrate and not stuck in either the open or closed position. However, when you remove the ISC, if you shake it and it's rattling, it's pretty much gone.