Ok. I have a 2004 Ford Explorer. The car is not cranking when the ignition is turned. New battery so that is not the issue. I am able to get the engine to crank by bypassing the starter relay. Checked the starter relay and it is working fine. Checked to see if I was getting voltage to the relay when the ignition switch is turned and that is full voltage. I am at my wits end with this. I would have thought that the relay was bad but it is not. I do not understand why nothing is happening.
With the dash lights on, step on the brake pedal and shift the transmission into neutral and then try starting the engine.
If the engine starts, it points to a problem the park/neutral safety switch.
Tester
Tried that and still nothing.
How do you know the relay is actually good and functional? You stated you get power to trigger the relay, which is good… but there are two other things the relay must do. It must energize the electromag inside and make the connection to trigger the starter. You need to prove that out…
Should be same relays within fuse box that you can swap in as a replacement…like say…for the horn or something. Try that…
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I am not 100% positive on this so take it with a grain of salt. I had a no-start condition on my Lincoln once and it was due to a faulty starter relay. That relay was in addition to and part of the car’s security system.
On my car this was located behind the glove box. Just some food for thought.
The relay is a multi-function relay and in addition to the starter circuit it may also provide power to the backup light switch and/or clutch relay. Getting power to the starter relay does not mean you are getting power to the starter. This is a multi-function relay and maybe provide power to the backup light switch as well, but on an internal different circuitry. Make sure you measure the voltage on the output terminal going to the starter. A new starter is only about $8-10.
Check both sides of relay coil. I bet you see +12 on both coil pins. One side must also be grounded for the relay to function…
The relay has 5 terminals. 2 for the control circuit and 3 for the starter circuit. Not sure why they have 3 on the starter circuit. Pin 30 is the constant power to the relay for the starter circuit and 87e is at rest position and 87 is the powered position. Pins 85 and 86 are the control circuit. The 1st thing I did was remove the relay and then put a jumper between 30 and 87 which the starter instantly started cranking. Next I put a tester in the empty 85 slot and when the ignition was turned there was voltage on 85. Everything looked good to here and I figured it was a bad relay. I tested the relay by putting voltage to pins 85 & 86 to close the relay. At that point the continuity between 85 & 86 dropped from infinite to 0 on an ohmmeter.
This may be the only thing it could be. I checked one side and got voltage and figured that was what I was looking for. Did not check the other. I will check it tonight and see.
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Yes you are correct about the terminal description…and it is good you tested the system the way you did jumping the panel side 30 and 87 to see if the starter reacts is precisely what you needed to do to test the circuit.
Often times you will have a clicking relay that has burned contact points internally so despite it seeming healthy…it actually cannot let current flow between 30 and 87.
I’m fairly certain you will have identical relays within your fuse box…there should actually be more than one that you can swap into the starter relays position as a quick test of this theory. Other than using a meter on the starter relay you removed… Not rocket science…
You are waaaay ahead of the game with the tests and knowledge you already have about how it all works. Cant tell you how many times me and the other fine people here try to explain relays, their terminals and the circuits they exist in. Its nice not to have to do that this time honestly. Im sure you will figure this out quickly. Let us know
Hope you meant to type the continuity between 30 & 87 dropped to 0
But is slot 86 grounded ?, could be a bad ground to the relay.
This is what I am thinking now. It may be a bad ground to the whole fuse block. Will check it tonight and let everyone know.
I tested the continuity on the load side and it dropped to 0 when energized, so the contacts are good. I have fairly extensive training in electrical and electronics. Over 25 years of experience, but limited knowledge of cars.
That may be your saving grace… Many posters we see would have already replaced the battery, starter and alternator in that order because they know how to do that but don’t know how to diagnose electrical systems! 
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After some more testing there is no continuity to ground on the grounded side of the ignition circuit of the starter relay. After looking at wiring diagrams the only thing on that side of the circuit is the neutral safety switch but putting it in neutral does not bypass it. Could that switch be physically broken to where it thinks it’s in gear all of the time?
Switch is failed open or wire broken? Time to ohm it out.
The PCM is not authorizing the vehicle to start. Are you using a key that is not programmed to the vehicle? Is there a security light on in the cluster?
I actually own an 04’ Explorer XLT myself and I have found some rather disconcerting issues in the wiring department.
I don’t know what Ford used for wire casing in these vehicles, but it is more like plastic than rubber if you know what I mean. In fact I believe I investigated a little bit back when I had multiple wire breakages out of nowhere and I believe the issue was the use of Soy in the wire casing?? Don’t quote me on that but…the wire casing material in this vehicle is horrible. I currently have several broken in half wires in my drivers door jamb as well as in the back on the rear hatch window… SO if you notice things that worked fine one minute and are kaput the next…keep in mind the wire problem…and look it up on the net as well. It seems to have gotten the attention of a “few” people out there who are none too happy about it. I recall the mention of Soy for the casing of the wires…but what I also did not like was the low strand count of the wires and their subsequent stiffness as well. Most of the wires, even small ones were more like solid core wire than stranded wires. Which did not help in the wire snapping in half department. Look into this on the net… you will find a lot of info.
@Nevada_545 brings up a very relevant point about being authorized to start. I have also first hand experienced ignition key failure…but when the key in this vehicle fails and the theft prevention system kicks in… it allows the starter to function and the engine to turn over… it just kills the fuel and spark or one of them anyway… however the engine WILL turn over with a key chip failure.
If you suspect the neutral safety switch then by all means prove it out… I believe Mr @Tester mentioned this prior. Perfectly feasible theory on how this issue could arise…it very well may be on purpose due to the neutral switch not allowing the starter to function.
Let us know what you find out about the switch… and do not ignore the state of the wires described above… if you have any small suspicion on wire integrity…those feelings are more well founded in this particular vehicle than any other I’ve seen in recent times due to the shoddy quality I and many others have complained about.
Were you able to get your Explorer started? I am in the exact same situation, I’ve checked everything you checked, line by line.