Yo Liam,
Welcome!
Check Engine Light (CEL) comes on when the electronic engine control system is not working properly. The check engine warning indicator comes on briefly when the ignition switch lock cylinder is turned to ON, and should turn off when the engine starts. If the check engine warning indicator does not come on when the ignition switch lock cylinder is turned to ON or if it comes on while the vehicle is moving, the system is malfunctioning
If the CEL does not light up at all when starting it; then suspect that bulb is burnt-out or loose, socket was damaged by PO or shop, etc. or someone removed it.
Is it on?
TRY a Self Test for Codes by my pal BroncoJoe19
Code Reader..... - 80-96 Ford Bronco - Ford Bronco Zone Early Bronco Classic FullSize Broncos
Heat the engine up; engine temperature must be greater than 50°F (10°C) to pass the KOEO Self-Test and greater than 180°F (82°C) to pass the KOER Self-Test.
Then turn off all accessories/lights, etc.
Make sure A/C is off and transmission is in Park (automatic)
Do Key On Engine Off (KOEO) portion first.
And Post em here according to
KOEO
&
KOER
***
See my Vacuum leak test in post #11 incl jowens126 's HVAC Control Panel info @
Help with dtc codes and idle
Excerpts;
"When vacuum leaks are indicated, search out and correct the condition. Excess air leaking into the system will upset the fuel mixture and cause conditions such as rough idle, missing on acceleration, or burned valves. If the leak exists in an accessory unit, such as the power brake, the unit will not function correctly. Or Air Conditioning when in MAX mode may switch to Defrost."
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Here are the 1990 Bronco Pre-Delivery Shop & Electrical & Vacuum Troubleshooting Manuals (EVTM), Partial by member Kingfish999 in Google Drive @
1990 Ford Truck service manuals - Google Drive
&
1990 Ford Truck Emissions Manual.pdf by Ford via member 90.CaliBronco in Google Drive @
1990 Ford Truck Emissions Manual.pdf
Suggest you download both for faster scrolling and to use the table of contents index.
1990 Ford Bronco Brochure by Ford via Dezo's Garage @
https://www.xr793.com/wp-content/uploads/2020/07/1990-Ford-Bronco.pdf
Haynes Red Manual for 80-95 Bronco & F Series @
Hanes guide 80-96 bko f series.pdf found by Mrs BroncMom!
AI