Brake controller- I would recommend the Tekonsha Prodigy 3. If you want to go a little cheaper the Prodigy 2. Both do electric and electric over hydraulic. Also very adjustable for smooth stopping.
You do need a 7pin connector on the bumper. Unclear from above if your have a 4pin or 7pin. You will also have to run a 40amp fused (Think resetting circuit breaker.) power to the trailer connector. Also the brake controller power line to the controller. Use a 10 or 12 gauge wire for both.
The brake controller will want brake light power, 12v+ and 12v- from the cab. The controller will send +0-12v as a signal to the trailer connector for the standard drum electric brakes. Electric over hydraulic disk will use 12+ and the brake controller signal.
My 95‘ F150 gasser had some wiring under the dash, fuse slot in fuse box, and corresponding wires under the hood ready to go for a brake controller. It had a slot for a 30 or 40amp jumbo fuse on the fuse box.
My 88 F250 diesel did not have wiring for a brake controller. But the PO had put in a cheap controller. Used his wiring for the cab but put new power and brake controller wires to the trailer connector.
So check the wiring diagram to see if your 1990 does have the extra wiring. Then check the fuse chart for a jumbo fuse marked trailer brake, tow wiring, or towing connector. (I believe it was marked for trailer or towing.) On my 95 it was 4 or 5 wires wrapped with no wire ends taped or zip tied by the steering column and the brake and gas pedals. I do not remember the fuse number but as I stated above, something about trailer or towing. Then 2-3 wires with no ends on the harness along the firewall or driver side fender well to use.
Post some pics!
If you have to do a new tailer connector use these. Life is to short to have vehicle side trailer light issues.
Cut and splice the male end into a junction box.
Mount on your frame and bring your wiring to this junction box.
If PO did a bunch of 3way crimp connectors start over with this plug in kit. Run it to the junction box above.
Trailer pin chart -