Experiencing an odd issue with my 1989 E150 4.9
Sometimes when I go out to start it, I get nothing when I turn the key on. I do hear the fuel pumps kick on as they should, but will not crank. If I go out and jump across the solenoid, it will start right up. It will go several days with no problems starting, then all of a sudden it'll have one of the above described fits. As I go to jump the solenoid with key on, I observe a "rotten egg" smell from around the battery,which is a Motorcraft group 65. What am I looking at here? ignition switch? battery getting ready to poop out soon? Issue is so random

 

Not sure about the battery but apparently it has enough power to start the engine when you jumper out the starter relay. I had a similar issue and it turned out to be the wire from the ignition switch that plugs onto the starter relay post. I used a pair of pliers and every so slightly squeezed in on it and it has been working fine since. The next time it doesn't start, move that connector and see what happens. If that doesn't work then use a volt meter and check the for 12 volts to that same connector when you have someone to try to start the engine. That will tell you if you are getting power on that wire from the ignition switch. You might even want to check that without touching anything else the next time it doesn't want to start. You should be able to get a DVM leed on the nut that holds the stud to the relay without disturbing anything else. Then wiggle the connector, then check it for for voltage if wiggling doesn't work.

IF none of that works and you don't have power to that wire from the ignition switch, you will need to trace that wire back to the ignition switch and ohm it out to make sure an intermittent open circuit, possibly a connector in between the relay and ignition switch. Next would be to check for voltage at the ignition switch. Lets hope for a loose connector at the relay though!

Oh NO I forgot about the neutral safety switch! Below is a diagram that I have in one of my saved files labeled 8849e350 . I am going to guess that my disorganized file system means 1988 E350 with a 4.9 engine. E150 or 350 shouldn't matter and i doubt a year or two would either but might.

Circuit 32 from the starter relay.

 

Your ignition switch itself may be coming apart
Interrogate the switch next time it happens

 

Mine was like that at purchase, the OP showed me how he was jumping it with a pair of pliers, and told me that his mechanic said it needed a new ignition cylinder.
I had it for a few months until eventually jumping it at the solenoid stopped working and I had to jump the starter directly off of the battery with jumper cables. That lasted for about a week then that stopped working as well.
Turned out to be extremely corroded ground cables. I replaced the starter to frame and the battery to body cables, then went ahead and added an alternator to battery ground as well. Haven't had any issues since.
I'd suggest checking your grounds before replacing any parts. Mine were green on the exposed copper and black about an inch into the rubber.

 

Was none of the above, Was a crack in the positive terminal, that I couldn't see from above. I replaced that, starts perfectly

 

Thanks for the update Jeff. Perhaps because of the bad terminal clamp, it didn't always have enough voltage for from the starter switch to engage the starter relay?

 

Could be, but it's fixed now. Only rotten egg smell I get now is when I accidentally rip a loud one as I'm driving :P

 

Happens to me all the time 😂