precisly..
an 86 will/should have had a few batt replacements in its life, and without knowing the state or age of the existing batt, or even if it had water in it, it's a coin flip...
there is easily enough juice in a marginal or bad batt to give you lights, and horn...but not enough to crank it...it will still actuate the relays, and solenoid, but choke when expected to offer the amps required to turn the starter....
don't bypass or circumvent anything at this point, get a battery and try it, or jump it, don't add another variable, or risk damaging things by going out of progression to anylize the system as it exists....you will be adding variables making it harder to find root cause. Un plug and replug in the harness, make sure it's connected, try the steps in progression to find what is actually wrong