Hi, I'm new hear and also a new f150 owner. A couple of weeks ago I purchased a 1990 xlt with rotted and broken left rear leaf spring brackets and shackle. I'm in the process of fixing that and found that the battery wont hold a charge over night. The old owner did show me a problem with what he called the fuel pump relay, sometimes you must shake it to get the truck to start. The only problem is it's in the eec relay spot in the relay holder under the hood. So I dont know if its really the fuel pump relay or what. If you touch it while the motors running it will kill the motor. I know it has a black connector on it... Also I read somewhere if you hear a clicking from a relay when connecting and disconnecting the bat. its bad, well one of the other relays does that and was wondering could that be my power draw thats killing the bat? The one thats clicking has a green connector on it and it wasnt in any holder under the hood so I dont know what or which it is. Any help here would be great.......

 

Might be staying closed causing the drain, just get another they are pretty cheap, under $20.00, or there is a wire crossed causing the relay to stay closed. Also check and make sure the head light switch is pushed all the way in.

 

Are all relays the same? Do I need to know which ones which?

 

Ok, so today I got out my multimeter and checked how much draw was on the batt with the key off. When I touched the terminal and the batt the trailer relay clicked on twice and the meter jumped to 4.8 something twice and then read 0.01. If I'm correct, isnt that fine? Thats telling me theres no draw correct? So whats killing my batt? Like I said I just bought this truck so I dont know whats happened in the past but it looks as though the PO. put a new batt in so to mask a problem. Dont know for sure. Last night I diconnected the neg side all night and it strarts right up today so I dont think its the batt itself. Any ideas?

 

The easiest way I've found to test for a power draw is to remove the ground cable off the battery and hook a test light between the ground post and cable if there's any type of short that’s drawing power the light will light up. But make sure that there's nothing on and the key is off. If you have one start pulling fuses then relays to see what circuit it's in. If none of the fuses or relays cuts the light off check the charging and cranking circuit.
The clicking from the relay is just the coil energizing closing the contacts. Are you hearing this with the key off or on? The coil shouldn't energize with the key off. If it is I would check the ignition switch first to see if there's a problem with it.

 

The relay was opening with the key off. But it does close.

 

Ok, here's what I got now. I thought it was only drawing 0.01 amps. But If I mess with the wires going into the PCM relay, it turns on and I get a reading of .43 amps. I bolieve I found it. But should that be able to happen? I mean with the key not in the ignition? Should I look in to the ignition switch or something? I guess thats' why the fuel pump relay keeps clicking on and off.......

 

Yep shouldn't be getting any voltage to the pumps or amp draw with the key off. You will have power going to one side of the pump relay contacts from the fuselink. but the pcm relay shouldn't pull in (click) untill the key is on. That sends voltage to the pump relay coil to power up the pumps

 

What would cause the PCM relay to have power when the keys off? Does it have a constant power and because it's bad it turns on the feul pump? And I bolieve it was one of the yellow wires where it enters the connector that I wiggled that made it come on. If I tap the relay while the trucks running the truck will shut off also.