Here's what I have, F150 5.0L manual transmission, no start, just clicks at both solenoids. I've cleaned every connection, all are clean and cables, where visible ,and ends appear good. The clutch switch looks good seems to work but there are a lot of wires on this thing so who knows.
Before this got to the point it is, it would take extra attempts with turning the key to get it started. It would just click and sometimes a prolonged application would get the starter going. After cleaning everything it now only clicks. I've bench tested the starter and solenoid with a battery charger, the solenoid engages very solidly and the starter will turn. I've tried a remote starter switch on either solenoid, nothing, just solid loud clicks.
Reinstall it and all it does is click. I can jump the terminals on the starter and it will start the truck. What and how should I check here? My battery is good with a full charge. I don't want to throw money at things and not get results. I've read other similar threads and they all seem to dead end with the OP never replying what fixed it. There are so many wires in this system wrapped in plastic conduit and for all I know one unseen wire could be bad.
Why are there two solenoids? For years Ford did well with a single fender mounted solenoid which was super easy to figure out.
Take a test light and put it on the wire going to the starter solenoid from the starter relay on the fender. Put power on the small post that has the push on wire. If the test light lights the starter relay is OK. If it does not then replace the stater relay on the fender.
Ford is using a starter relay on the fender so the Ignition switch does not have to carry the larger current for the starter solenoid down on the starter.
It is still a very simple starting circuit to trouble shoot.
So even if I hear it click, it can still be bad? I tried the remote starter switch on it and it made the solenoid on the starter click.
Yes even if the starter relay on the fender clicks it can be bad. The contacts can not be making contact. Image below.
But if your starter solenoid mounted on the starter clicks and it bench tests good then you have a ground or power cable problem from the battery to the starter.
Where does your big ground cable from the battery ground to?
If it is not the engine block then that is your problem.
The frame is not a good place to ground the battery as there is not a ground path from the frame to the engine block to carry the high current.
The starter solenoid was at fault. I ran one more test with starter removed with the starter hanging off its wires and a set of jumper cables for a ground. The starter barely turned when turning the key. The motor itself turned fine when jumped directly.
A trip to NAPA and a wallet $36 lighter solved the problem.
I still think two solenoids is a bunch of BS as Fords did fine for many years with just one. Trouble shooting would have been way easier too.
Part number is MPE ST406SB should someone else need one.