I have an 89 Bronco that will not start with the key. I have replaced the ignition switch. The only way I can get it started and running is by shorting the two large terminals on the relay (passenger side wheel well). I have also replaced the relay as well. Anybody have any ideas what the problem might be?

 

Try running another ground wire to the base of the solenoid. The sheet metal the solenoid is bolted to has probably corroded and is not making a good connection for the solenoid to operate.This would be a good time to check all the ground wires you can see, clean them and place some grease or even vasoline over them to reduce exposure to the air and moisture. Usually works!

 

+1
If you can jump the solenoid it is either a bad wire/ground or bad solenoid.