You need a digital Voltmeter with pointed probes. Use a MV range 200 to 500, you do not need a high-end meter, cheap one is OK. Turn key on, but not start, headlights on high, blower on high. This loads the battery cables up to a high load. Measure voltage from pos battery post to other end of cable, which will likely be the bolt in the fuse box. This bridges from post to screw to see if anywhere along the line there is a weakness. Do the same for ground post to engine block, and also to the body. Should be 100 millivolts or less and steady. Now, you might logically think that there would be little loss to the engine block as it is not under any serious load and the big ground cable. But, there is a secondary ground strap from the body to the engine near the firewall so the load is split between the two ground cables from the battery. Key is, 100mv or less and steady.
Now, turn the lights and blower off. Start the engine. Alternator should be charging hard as you have used up some of the battery topoff voltage. Measure from the ground post of the battery to the alternator housing. You are checking the ground from that to the engine block and more. Again 100 MV or less. If your alternator is accessible, measure from the big screw, output of the alternator to the positive battery post. This checks the integrity of the large wire from the alternator to the battery. In this case 200mv or less.
IRCM = integrated relay control module. CCRM = constant control relay module. 2 names for basically the same relay / electronics box. Contains 5 relays (EEC power, fuel pump, fan low speed, fan high speed, and AC clutch) and some timing / control electronics in the form of transistors, resistors, capacitors, etc. It is a black box roughly 4' x 4" with a 30 pin electrical connector. Located under the fan shroud on the driver side.
OK, I have preformed voltage drop tests. Have minimal voltage drops on the positive cables and same on neg side. Had a little corrosion on the battery terminals. The neg post clamp broke when I tried to take it off. Cleaned up terminals and put on a neg post clamp. IRCM still buzzed. Took my handy ice pick and alligator clip jumper, applied a jumper wire directly from the neg terminal to the Blk/lt gn wire at the IRCM connector. IRCM still buzzes and engine will not start. I am open to any and all suggestions. Too bad this beast is not as simple as my 76 Chev 350. I know how to work on it.