hello from oregon, both tanks quit working at the same time on my 86 f250 diesel, i see there is a purple with a yellow stripe on one side of the sending unit front tank at the top and a dark solid black wire on the other side, one goes to the fuel switching thing on the frame rail and the black solid goes to the cab some where, witch wire is the ground wire anyhow? thanks for any help, the sending units were replaced buy the previos owner,gary

 

I cant remember but check and see if theres a fuse for them. Being both quit at the same time it sounds possible

 

Does your cluster have the IVR (silver box) instrument voltage regulator on the back. Get replacement at Ford or ap stores, start there.

Next would be the connections on the FSV (fuel selector valve).....inside frame rail drivers side.

 

I would check the fuse also. It controles the fuel selector switch too.

 

thanks, i will get a new ivr if it has one, all the fuses seem to be good in the fuse holder box.