hey guys 1990 f250 7.3, when i pull the light switch on the tach goes out of wack and the oil pressure gauge sky rockets, any idea what causes this to be happening, never ave i ever seen such a thing any help appreciated

 

look for ground problems

 

where does one start to look for a ground problem?

 

anywhere that the factory wiring grounds out. a wiring diagram would help to tell you which grounds are used. but if you dont want to take that route just start running grounds from the cab to the dash and whatnot

 

so your saying that a ground has come disconnected?

 

could be and could have corrosion and could be broken some where

 

anyone have an idea where i could find a wiring diagram on the internet? is this a common problem?

 

that isnt necesarilly the problem but its a good start. as for wiring diagrams. i get mine from alldata.com but itll cost you about 15 bucks. you wont find a thorough one for free most likely