I'll try to trouble shoot it tomorrow.  I know both fans are on sometimes.  So communication between the electronics may be faulty.  Fans have to kick on when the engine builds up excess heat.  

I just looked at the wiring diagram for the cooling fans. The ECU in your 96 uses the same 2 pins as our 97 to control the main and sub fan relays (4 relays low and high speed). Pins 73 and 74. If need be we'll get into that later and I'll explain how I fixed our 97 fan circuit. On it only the sub fan would run when the engine warmed up.

First, under the dash steering wheel side, you will find two 2 pole test connectors with one wire in each plug. Plug them together. Turn the key to on, "do not start". That starts the cycle. The fuel pump will turn on then off, the A/C clutch will pull in then release, both fans will turn on low speed then high speed then off. This cycle will continue until you turn the key off.

Unplug the two test connectors.

Did both fans run low then high?

If both fans run low then high, that means the fans, relays, multiple connectors and wire is all good.

Next, start the engine and let it run until the fans kick on.

Do both fans run, or does only the sub fan run by itself?