Hey guys,
hoping someone has dealt with this issue before.

I have a 92 laredo cherokee with a towing hitch and 7 pin wiring attached. when I turn the key to turn the electricity on inside the car (without starting the engine) I hear a noise for a split second in the rear of my car like something machine/ electrical like turned on. When I actually start the engine and am driving the car, that noise becomes constant. It's a pretty loud humming sound. I thought it might be something with the wiring harness for trailer power adapter, however when I put my ear to the back inside the trunk, it seems like the noise is actually coming from underneath the car near the rear skid plat and differential. What is this sound? Is this perhaps normal? Any help would be much appreciated.

Happy new year

 

From your description I would say it sounds like your fuel pump in the tank. I do hear mine when turning the ingition on but not when the engine is running.

 

x2 on the fuel pump. I don't recall ever hearing mine. I'll pay attention next time.

 

X3 on the in tank fuel pump. If this is a new sound that you have not heard previously it may be a sign of impending pump failure.

 

Thanks guys. After researching about the pump it seems that is the culprit. However, someone on another forum mentioned something about a ballast. Could that be it?

 

A ballast is unlikely. A pump is the much more likely to be the source of the noise. I have had electric pumps start making noise and fail soon after. Again, if this is a new noise that you have not heard previously, plan on replacing the pump soon.

 

My fuel pump makes that sound, the PO said he had it replaced just before I bought it, I hate it but I've grown used to it.

 

As in "the fuel pump will be quieter if the ballast is working correctly?"

 

Better yet, is it still there?

 

I've just inspected my ballast resistor and the two plugs that attach to the prongs of the resistor are terribly corroded. What is the technical name of those two plugs? Where can I buy them?
thanks!

 

I believe standard insulated 1/4" female spade connectors will fit. Hardware or auto store in the electrical section should have them cheap in a variety pack. Use a blob of silicon grease on them to keep the replacements from corroding since they're somewhat exposed to the elements. I don't recall the wire size. 16 or 18 gauge would be my guess.

 

I don't have a ballast resistor on mine, so I can't check for you, but I think you are looking for a 1/4" spade terminal. https://www.delcity.net/store/Push!O...inals/p_801898

If you want cheapos, any hardware or auto parts store will have them. Don't get cheapos. Get good quality nylon insulated fittings ( and use https://www.delcity.net/store/Ratcheting-Crimpers/p_10382(also or even https://www.lowes.com/pd/IDEAL-Non-Insulated-Insulated-Terminal-Crimper/999960629). Don't use those https://www.delcity.net/store//Crimping-Tool-&-Wire-Terminal-Kits/p_802248, and do NOT use pliers!!!!!

 

I would further recommend that you get heat shrink insulated wire terminals that way you can seal the crimp.

 

The fuel pump runs just fine without the resistor. Connect the wires and you are good to go. I did this on my 1990 XJ a few years ago and no problems encountered.

 

True. The ballast resistor is there only to reduce noise on the fuel pump. Bypassing it will not change fuel pump function in any way.