Ok, searched around and found 1 post that I think might help, but want to get opinions anyways....

97 explorer, 4.0 SOHC. Vehicle had bad engine, but would turn over with key. I put another engine in it, and now it won't start with key, but will start and run (runs real nice) when you turn key to RUN and jump relay (the one on firewall, that looks like a solenoid to me).

Now initially I thought there was a bosch style relay that was used for this. I'm wondering if it has something to do with the anti-theft after reading the post. It's the one in between the bigger relay, and the micro relays that are housed in the relay box next to the battery. I was testing it (what I thought was the start relay) and terminal 87 is hot all the time, terminal 86 is hot until you turn ignition to start,then it shuts off, the 30 is ground???? That seems all backwards from any other relay I've dealt with. Is it because its the "anti-theft relay"?

Just trying to understand the circuit...if someone could clue me in, that'd be awesome!

Frank

 

I agree, those voltage readings make no sense at all.

Heres how the circuit works.

Turn key to start & voltage flows thru fuse 24

Next up we have the anti-theft relay.

Next stop is the transmission range switch

Then on to the starter relay which feeds voltage to the starter solenoid.

Locations: fuse 24 is in the interior fuse panel

Anti theft relay is behind the center section of the dash. The relay contacts are normally closed. If truck is being stolen the remote anti theft/RAP module grounds the coil side of relay & opens the relay so truck wont crank.

Starter relay is mounted under the hood drivers side fender.

Hope this helps.

 

So what is the relay that I've been messing with beside the battey? It clicks when you turn key to start.

I'll trace power next chance that I can mess with it...I have a feeling it has to do with the neutral switch. Would it start in neutral if there was a problem with this circuit?

Frank

 

Hard to say from here what you're looking at, but the wiring diagrams show a typical Ford starter relay. The relay connects to the battery positive on the solid red cable.

The solid black connects the relay to the starter solenoid

Red/blue stripe is the trigger wire & connects the relay to theTRS/transmission range switch/neutral switch.

Yeah, if the TRS is bad it might start in neutral but not park.

 

Bueller, were you making your measurements with a test light or a digital multimeter (DMM)? The reason I ask is because the high input impedance of a DMM can cause you to achieve readings of ground and power due to parasitics throught he circuits they are connected to (ie: and open circuit may appear to have battery voltage or ground). A test light requires enough current that it shouldn't cause as much confusion when making such measurements. One problem with the test light though is it could actually trigger a relay coil depending on which terminal you connect to.

-Rod

 

On second thought that relay near the battery that you say is clicking, should be the starter relay.

Have you checked the connections at the starter??

 

Actually, I was using a 6-12 volt test light. The meter crapped out on us, so that was our only option anyways. It just seems really weird that it the test light was lighting up where it shouldn't have. If that is the starter relay (by the battery), it makes me think that voltage is coming back TO terminal 87 like there is a bad diode somewhere, or there are some wires backwards. I'm pretty meticulous when it comes to making sure everything is hooked up. The connectors are unique to each other, so I don't think that's an issue.

In my experience, when there's something weird like this going on, its a ground issue. The battery is grounded to the engine and the body, and the engine is grounded to the body. I had to shorten the ground cable up a bit, and it now goes to an alternator bracket bolt, instead of a bell housing bolt, but that shouldn't matter...

Everything works great. It runs good, it's charging at 14+VDC...it just doesn't want to start with the key.

I did check battery connection at starter...good. I also took the test light and checked for power at the small red wire at the starter. No power when turning key to start. That wire is the trigger to pass voltage through the starter, correct?

I had my partner look for the anti-theft relay, but he couldn't hear it clicking. I guess he wouldn't, if it stays closed. Does the thing open when you're not using a key to start it or something? He had a hard time finding it. Said he saw some relays under there, just wasn't sure which one it was.

The two other things I can come up with is that either there is something wrong in the harness that came with the engine (which I don't think has anything to do with startiong the vehicle), or something to do with the wire strands I spotted by the PCM connector. There were some bare silver wires laying atop the rest of the wires under the electrical tape. I removed tape at the same spot on the original engine/harness, and it looked the same way. Is that supposed to be some kind of shielding wire for the PCM??

I appreciate the help, guys!!

Frank

Frank

 

I'll have to check the wiring diagram this evening to see if I can make any sense of the measurements you're getting on the relay.

-Rod

 

Maybe i can help with this.

Heres how the starter relay is wired.

Turn the key to start & the red/blue wire has 12 volts on it

The relay closes & now solid black has 12 volts on it.

The solid red is from the battery & is hot at all times.

At the starter (solenoid) solid black has 12 volts coming in from the starter relay. Trigger voltage

Solid red is from the battery & is hot at all times.

Bueller in your 1st post you said that you turned the key to run & jumped a relay on the firewall and it started. But the diagrams do not show any relay on the firewall. I wonder what thats about????

Also you said that you checked for trigger voltage on the small red wire at the solenoid. In the diagrams that is a small black wire. I wonder what thats about???

Could a previous owner have done some creative rewiring on this thing???

 

Maybe it's appropriate to ask if when you can't get it to start does the starter motor turn the engine over, it just doesn't start, or do you only hear a click and the starter doesn't engage? I realize you said that the relay clicks when the key is turned to Start but it's not specified if the starter motor engages or not. Some people use the phrase "won't crank" to mean the starter motor doesn't engage, others intend that the starter turns the engine over but it doesn't start.

-Rod

 

Ok. Relay I am referring to is on firewall. It has a large gauge wire coming from battery, and a large gauge wire going to starter. There is small post on it that that triggers the relay (and its color is red with a blue tracer).

At the starter, is about a 12 ga. red wire going to a male spade on the solenoid. There are two posts on the starter. One connects to the relay, the other connects the solenoid to the starter motor itself.

I messed around with it a bit tonight. He finally bought a book for it, so now there's a wiring schematic to reference to. All the wires are correctly colored according to book.

The starter DOES turn engine over. To check relay, I used a jumper wire to go from battery positive to trigger post on relay, and it turned engine over and ran. So the relay, and associated wiring for actually starting vehicle, are in working order.

I started tracing power. I've got power going through ten amp fuse, power going to anti-theft relay on red/blue wire, power coming out of relay on pink wire (this is all with key at start position). Now from there, if I'm reading/remembering schematic right, it should go to neutral switch at transmission connector via pink wire. If I'm understanding correctly, when trans is in PARK position, it closes circuit, and power should go from pink wire out to red/blue wire, which engages relay. The red/blue and the pink wire, are housed in a 12(?) place connector going into the shift mechanism on the drivers side of the tranny. I thought one of you's said it was a two place connector. Am I looking at the right thing?

I have no power coming down to park switch on the pink wire. So I'm thinking there's either a connection I failed to investigate between theft relay and park switch, or there is an open on pink wire. It shows a starter clutch safety switch jumper (for Automatics) after the theft relay (if memory serves anyways...getting late, and there's some brain fade going on), and not sure what "jumper" consists of other than a piece of wire. That's where I'm at atm, till tomorrow night.......

Frank

 

I'm glad to see that this is not a problem with the PITA/anti theft nonsense.

The neutral switch has 7 wires into it & 4 wires out.

If you remove the connector you should see 12 volts at the pink with key turned to start.

If you see that voltage the neutral switch is shot or red/blue is open between the neutral switch & the relay.

With the connector removed you can probably rig a jumper from pink to red/blue & if it starts the neutral switch is shot.

Nice job tracking the voltage & if you do need a new "neutral switch" The official Ford name for it is the "transmission range sensor"

 

OOPS, you did say theres voltage leaving the anti theft relay, but no voltage on the pink at the neutral switch. So it looks like theres a break in that wire.

My wiring diagram shows 3 connectors in the pink between the anti theft relay & the neutral switch. One of those might be disconnected.

 

Problem resolved!

I came up with the same solution. A break in the wire between the firewall, and the "TRS". On our path to track down the open, my buddy was comparing wire colors on the gray connector coming from the engine wiring, and noticed that none of the colors matched up to the mating connector. DOH! On the swapped in engine, there were actually 2 holes left blank on top of that! I removed the intakes, and swapped the original wiring harness back in (cutting and soldering in the MAF sensor wiring and 2 ground wires at the PCM AGAIN!)
I still can't figure out why the harnesses were different. The only other difference between the colors and the 2 blank holes, was that the alternator wires came with the junkyard engine's harness, and the trucks alternators wires were seperate from the engine harness. I noted this as odd when I put the engine in, but it was charging, so I didn't really think anything else about it.
The junkyard engine came out of a 97, and everything was exactly the same as the original engine down to the A/T flex plate. I could see it being different if it came out of a manual truck, but that wasn't the case. The only other thing I can think of, is that maybe there was a mid-year change, and Ford didn't bother to let the little people know..........

But the important thing is that its fixed now....

I just wanted to thank you guys whole heartedly, for helping out! I've tried throwing issues out there like this in other places and don't even get a response....

THANKS!

Frank

 

So thats what the problem was. As you say sometimes there are build date differences in the wiring.

Glad you found the problem & congrats on the fix.