1995 Ford Aerostar 3 Square Diodes Under The Hood

Those "diodes" are actually relays, and will only fit in one way! I don't know about your red wire, can you circle the one yoy removed?

Thank You for getting back to me. Sorry for calling the relays Diodes. Shows how much I know. The relays each have a different number on them and you are correct that they will only fit in one way but they will and are able to fit in each others slots ; 1 into 3 and and 2 into 1 and so forth. I have the three relays in the wrong slots. The red wire that I removed is the one that is the largest. This wire comes from the battery. I don't know where the small wire goes but I didn't remove it. I'll take another photo for better reference.

Thank You Again Merlin2021

The relays are interchangeable, dont worry about where you put them in. I don't see the disconnected wire? You can drive the van to an Autozone and they will test the charging system for free, but it sounds like a bad alternator.

I have a similar issue, only I lost one of the items in main picture above. The whitish/beige plug at the bottom, after the 3 square relays. What is that plug called? Is it a fuse/relay/diode? I'm lost, please help.

In the first picture there are relays and in the second it is a starter solenoid. Can you upload a picture of which one you are talking about?

Thank you for responding Ken L. It's the fourth thing down, after the black diodes. Here is a picture.

Does it come out of the fuse panel?

Here is reference on position of diode box / box with diodes...

You can see in the second picture (closer there further), where the item doohickey is missing. Looks like just another 5-prong diode would do... but that's not what was there before.

Yep, it could be a circuit breaker or thermal limiting fuse they don't tell us what it is unfortunately.

Alright, thank you Ken L I'll look into it further. At least u have more to go on...

What are you using as a reference btw? A book?
Asking for personal research purposes.

Thanks again

We use AllData and Mitchell 1 for reference. Please let us know what you find.

Well, I went to pickNpull and found what I needed quick. The thing is I can't find an image or sale item that looks like mine. When I went to dealership, what they wanted to sell me, was too small (by about half from what I recall).

It says "DIODE" on top, along with what I assume to be the diode symbol. I typed in the series on characters found on diode (F2TF-14A604-AA), and the closest I found was "universal" and black. Might have been shorter too. Also, the "universal" diode code was lacking an A at the end (F2TF-14A604-A).

My diode also reads "6CA" (which you can see in picture), then "PP" under that (with full serial code above those).

I still have no idea how to identify or locate if lost again... aside from PnP.

If you have any insight Ken L, I'd be happy to hear it.

It looks like a 60-amp thermal fuse but I am not sure, that is a mystery alright I will pass this onto my other experts to see what they say.

Cool. If anything turns up, please let us know as I'd like to identify it in case of future mishaps.

Since it's directional and only goes one way I would say it has to be a diode. It's a one way filter.

WRENCHTECH,
It's definitely a diode, it says so on top. Would you call that a "one way filter diode"?

That's what a Diode does. It only allows current to flow in one direction to prevent feedback in a circuit. This one is a diode for the PCM relay. Here are the diode color charts, the ID of the diode and the wiring diagram.

Hi guys. Allow me to add some clarification. All relays use an electromagnetic coil of wire to pull on a movable contact to turn on the high-current switching contacts. When first energized, current builds up slowly, not instantly, as that current creates a magnetic field that opposes the current creating it. That is normal, takes just a few microseconds, and is exactly the same thing that happens in an ignition coil.

When that current is switched off, (think of opening breaker points on an older car), current flow has no choice but to go to 0.00 amps instantly. That extremely rapid collapse of the electromagnetic field creates an "inductive kick" that develops a huge voltage spike. In an ignition coil that spike is at the heart of how the circuit works. It can be as high as 300 volts. That gets transformed, or multiplied up to 15,000 to 40,000 volts in the secondary to fire the spark plugs. That inductive kick is desirable and necessary.

That same inductive kick occurs in the relay's coil when it is switched off, but here that used to be turned on and off by a mechanical switch. Those don't give a hoot about voltage spikes. Today relays are usually turned on and off by computer circuitry. Those transistors have very specific current and voltage limitations that are designed in for specific applications. Transistors are extremely intolerant of those voltage spikes. Once a transistor shorts, it's done and that computer has to be replaced. To prevent that damage, they put a diode across the coil of wire. It's in there backward, so when it's energized, it's like that diode isn't even there. (Diodes are one-way valves for electrical current flow). It's when that voltage spike is developed, with its reversed polarity, that the diode becomes "forward biased", meaning the voltage polarity of that spike turns the diode on, then it conducts a little current to short out that spike. That removes the threat of damage to the computer controls.

Generic relays often do not have a diode. If one is needed, it is installed in the rest of the circuit. It could even be soldered to the terminals on the relay's socket.

As a point of interest, if you see the 1" cube gray relays in a lot of GM vehicles, with four terminals instead of five, and they're in a square pattern, those relays do not have diodes. Instead, they use a resistor that under normal operation is high enough in value as to have no effect on circuit operation. When those relays are turned off, the voltage spikes kind of get absorbed by the resistor. They aren't nearly as effective, but they do a good enough job, and the advantage is those relays can be installed into the socket two ways and they'll work just fine either way.

When the relay has a built in diode, the coil has to be wired with the correct polarity. If you try to use one in a custom project and connect the coil backward, you'll have a short circuit and usually some smoke. You can't plug them in wrong in the relay box. The polarity was designed in by the engineers.

To finally answer the question, Ford often prints "Diode" on the relay covers to denote there's a diode in there across the coil. We don't customarily see that on other relays, hence the confusion. It's just a regular relay, but they're telling you there is voltage spike suppression built in.

In other applications, Ford was famous for trying to use up a huge inventory of parts purchased when building older models. Instead of letting those sit on shelves for years, they find a place where they can be used on a current model, but they might have to add something, in this case a separate diode. Rather than buy millions of new relays and let millions of in-stock relays sit, they just design a diode that can be plugged into the circuit. Because those diodes do have that polarity, the terminals are oriented in such a way as the assembly can't be plugged in wrong. Those could be used with a relay, or, as Wrenchtech mentioned, to isolate one circuit from back-feeding another circuit, such as when they both share a common ground. In those circuits, they can be expected to have to pass a certain amount of current. The more current and the higher voltage a diode can handle, the more expensive it is. They will have different diodes with different ratings so they can use one that is the least expensive they can get away with, and spend more only for those that are used in higher-current applications. This is where you might be able to switch them around, but typically if those differences are important enough, they'll use different terminal spacing so they can be mixed up.

CARADIODOC is right its a Flyback Diode for the magnetic field collapse of the relay coils.

Nice, makes sense, go team!

Hi AL514. Sounds like you have some background in tv repair.