I have a 99 F-150 (5.4L...4x4 auto trans) that wont start. I tested the starter and it turns. If I connect it directly to the battery it will even start but when i jump in the cab and turn the key...NOTHING. All lights come on and no warnings. I've elminated everything but the STARTER RELAY and the TRANSMISSION RANGE SENSOR. How do I test both of these?

My ideas so far...I think as long as I disconnect the Tran. Range Sensor from the starter relay and it still doesnt start then its my relay...but if it does its my Trn Range Sens. Do my logic completely elminate one or the other??

 

Relay? If the suspected bad part is in fact the relay, your logic makes sense (not sure if just disonnecting the trans would do it, may have to be 'jumped'). I'd be cautious though...there's also wires and connections involved. Also, I'd imagine if you looked at the other relays in your relay box, you'd find one that would fit that you'd be able to swap temporarily to test the theory.

 

typo...yup I meant starter relay....however, the starter relay is not a interchangable relay. But I think its the problem anyway...




see the orange wire...that just pulls off. its the transmission range sensor. suppose to tell the relay if the vehicle is in park. I disconnected it and the truck still doesnt start. after alittle reading and some help i'm hoping I can emlinate the tranny sensor.

 

The MLPS/DTR sensors were known to have a water intrusion problem in the mid-90s; IDK if yours is the old style, or the updated one. In any case, check fuse 21 in the dash, & then probe the DB/Or wire going to the DTR & the Tn/R wire coming out, going to the starter relay near the battery.

One of the R wires going to that relay should be hot at all times; the other should go hot when you apply 12V to the Tn/R wire, and the relay clicks.

 

There is a starter solenoid on the firewall. Jump it with a screwdriver, or wrench. Turn the key on and try it. If it cranks then you've found the problem. It's about an $8 part most places. I learned about this with my 99. Good luck.
Rich

 

It was the starter relay or starter solenoid located on the firewall. All replies were very helpful in tracking down the problem! thank you!