Where do you connect a code reader?

Typically it's near the right rear corner of the engine compartment. It looks like an odd non-symmetrical triangle with an extra single wire for the fuel pump.

Here is a guide to help you

https://www.2carpros.com/articles/ford-lincoln-mercury-obd1-1995-and-earlier-diagnostic-trouble-code-definition-and-retrieval

The fuel level sending unit is not monitored and there won't be any fault codes related to that. Running problems caused by circuits and systems monitored by the computer will turn on the Check Engine light if that problem could adversely affect tail pipe emissions. Most misfires and running problems fall into that category.

Sounds to me like your fuel filter is dirty or maybe even air filter. I have a 94 ranger with that same exact problem. Change both filters its not expensive and is very easy to do. Just pinch of the cord down from the the fuel filter and unbolt the two connections. As for where to connect the reader, there is a plug on drivers side under hood. It is located just up form the fuse block and is the only cord under there that does not have a connection.