My aftermarket dual electric fans that I installed recently (chucking the engine driven fan) stopped working the other day.

An hour or so of tracing voltages took me to the familiar blue diode pack located on the LHS just forward of the brake master cylinder. I noted that the connection with the two green wires was putting 12V into the pack, but the single green wire that runs to the thermal switch was only seeing 5 volts, which I guessed wasn't enough voltage to trigger the fan relays.

Popping the case on the diode pack showed considerable corrosion on the circuit board that the diodes are soldered to. Cleaning this up didn't help. Measuring the resistance across the diode in question, it was will over 2 million ohms!

I mess around with electronics a bit and happened to have some diodes lying around (for those that don't they are dirt cheap at Radio Shack or other electronic shops). Snipping the old diode out and soldering the new one in place was a quick job, and now my fans run again :-)

I noted that my diode pack was tilted down, so the bottom of it (where the connections and the seam between the cover and the base is) would be prone to collecting water over the years. I drilled a hole and remounted it so the case is up and water will have to work a little harder to get in.

I don't know what the diode pack costs "new", but I didn't see a diode in there that would cost more that $1 each to replace.

Cheers,

John
1987 XJ-S V12, 62,000 miles

 

My diode pack went out. All the wires connected to it are green, so i cant tell you which, but i made a jumper between 2 and my fan now comes on with the ignition.

 

Good work !


Cheers
DD