Do you have a FSM for the truck? There are some really good troubleshooting charts in there. 30+ year old electronics can be cranky.
A no-start situation is different than a no-spark. I'll try to remember what I can for both.
There are several things that need to go right to start one. Cranking voltage cannot drop below around 11 volts or the ECM may not trigger. I think 10.4 might be the cutoff or close, but if you get lower than 11, often they won't light off. The AFM connector needs to be making good connection. An unhooked AFM will normally start, then die immediately, but I've had one fail to start with the AFM disconnected a time or two. Grounding problems are very common when one has been subjected to water intrusion. Even though the ECM is behind the glove box, there are several grounds that can give you fits. Always check them all out thoroughly. Should be one from battery to passenger side inner fender, one from cylinder head to firewall, one from near the starter to the frame, a couple behind the speedometer and possibly some from the ECM area to the body. Those are the critical locations for cranking and running. There are also grounds to the headlights if you figure out they aren't working.
There is a relay in the lower right kick panel, I think that is the one you mentioned checking. You can disassemble them and check inside for corrosion. If it sat in water, you will get battery voltage out of it, but it won't carry the amps necessary once a load is put on the circuit. If the distributor got water in it, and it is original age, the wiring inside may have degraded or shorted out. In mine, the inductive pickup coils failed with corrosion and it would intermittently start and run bad. New distributor fixed that problem. If the ignitor is getting weak, it will do the same thing. I believe there are troubleshooting procedures for the ignitor, but I don't remember them. The bad thing, is a distributor that shorts internally can smoke an ignitor and last I looked, a chinesium knockoff was almost $400. They haven't made a Toyota ignitor for many years, unless someone has figured out a subsitute. They are application specific for the 3FE, so you can't substitute one from a mini truck or a camry and make it work, or if it does, it probably won't work correctly.
Make sure the starter switch has not gone bad. If it is not energizing the ECM while cranking, nothing will work. A quick test is to see if you get spark in the split second you release the key from the cranking position back to the run position. Symptoms of that failure are common to most vehicles. You crank the motor over for several seconds and the engine lights off as soon as you release the key from the start position while the engine is turning over relatively quickly.
