'88 MJ Electric Fan Diode Replacement?

'88 MJ 4.0L has cooling issues, which I been through pretty much the entire system, and I'm still running hot and eventually overheating.

The only thing that isnt' working correctly at this point is the electric fan isn't kicking on when I turn the A/C on, nor when the engine gets hot and the coolant light starts glowing red.

The fan is good, my temperature sensor in the radiator is brand new, just replaced the relay, so the very last culprit is going to be the orange plug diode that is spliced into the harness.

I have absolutely no interest in wiring in a manual switch for the fan to come on, as I'd rather have it work automatically.

With that said, I've called about 5 dealerships and the orange diode is no longer available from the factory.

Its a 3 Pin, 5A diode, which I'm having trouble finding a replacement.

Aside from junkyard hopping, does ANYONE have a source for a replacement, whether thats OEM or aftermarket that I can splice in place of it?

Here's a pic of what I'm talking about:
http://www.lunghd.com/Tech_Articles/Cooling/Overheat_Diagnosis/fan_diode.jpg

Thanks for the help!

Diodes are easy to test with an ohm meter. They should have near zero ohms resistance one direction and infinite resistance the other direction. They are like a one way valve.

That diode is a booger, even my tech guys at work could not find a replacement! Not to sound dumb but are you certain it's overheating? The reason I ask is I "thought my 89 was overheating" but the temp sending unit was malfunctioning! It would spike to 230* rapidly as the engine warmed up so I would shut it down. I kept looking for why the fan would not come on until I touched the hose and realized it was not hot. A new NAPA sender and all OK. (The NAPA reads a little higher than it should but close enough to know I'm OK.)

b5blue said:

That diode is a booger, even my tech guys at work could not find a replacement! Not to sound dumb but are you certain it's overheating? The reason I ask is I "thought my 89 was overheating" but the temp sending unit was malfunctioning! It would spike to 230* rapidly as the engine warmed up so I would shut it down. I kept looking for why the fan would not come on until I touched the hose and realized it was not hot. A new NAPA sender and all OK. (The NAPA reads a little higher than it should but close enough to know I'm OK.)

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It is basically a three pole rectifier diode, it is just some lowest bidders version of a more expensive one. You can make your own with two ten amp diodes or buy something heavy duty like a three pole rectifier diode maybe 30 amps, for around ten bucks at most any electronics store. You can even buy crimp connectors that fit the legs on the rectifier diode close enough (you may have to spread the (size small) female spade connector loops just a little.