Hey everyone, I've got a ? about why my battery dies. I have a 1990 f350 7.5 and the battery dies if it sits for more than 3 days. I tried a brand new battery and the same thing happened. However, if I disconnect the starter cable from the starter relay the battery is fine. Does that mean I most likely have a bad starter relay, or starter solenoid??

 

Just the cable to the starter, or the + cable from the battery?

 

Just the cable from the starter to the relay...at the relay. The battery cables are still making contact with the relay and battery.

 

No idea...

That post should be isolated from anything electrical unless the ignition switch is in the start position.
The relay is inexpensive and easy to replace, but I hate to just throw parts at a problem "hoping" to fix it.

I once had a situation where the plug going to my alternator had melted and shorted internally.
That got me a new battery and caused some cursing for a few days until I found it.

 

Yeah that's exactly what I'm trying to avoid. This truck has a myriad of electrical problems and just replacing parts gets expensive real quick. If it was a bad relay, wouldn't my truck not start at all?

 

It could also start, but not disengage.
It could leak voltage to ground, through the mounting plate.
They don't always fail in the manner you describe...

You say that if you disconnect the cable to the starter the draw goes away.
Have you tried connecting a voltmeter from that post to ground while the starter cable is disconnected?
This would "prove" your theory and show the relay to be the culprit.

 

That's a good idea, I'll try that tomorrow and let you know how it goes. I think I get what your saying about the ground too, so if it's a normally closed circuit it's stuck open. Constantly drawing current from the battery and leaking to ground through the starter...but wouldn't that fry the starter solenoid and once again it wouldn't start at all??

 

Ok couldn't wait till tomorrow so I went and tested the relay. There is no voltage at that post whether the cable is attached or not, or on the centre post. There is power on the third post where the battery cable is mounted. Where does that leave me...lol.

 

Well,
If there's no power it can't be leaking there.

I would start by checking the other wires connected to the same post as the cable going to the battery.
There will always be some draw for computer memory, radio memory, etc. But this is only milliamps.

Check each wire separately using the ohms scale with the other side of meter connected to ground. If you find a very low reading that's a place to look.

If the wire going to your alternator has continuity that's a sure bet that either the regulator/rectifier or the plug I mentioned has failed.

Some circuits are always hot, like the interior light, cigarette lighter etc..
Be sure the door is closed so the interior light is off while testing.

I don't have a schematic for a 1990 truck so can't tell you exactly which wire may be drawing power.
Do you have a shop manual?

If neither of these, then you could start removing fuses one at a time to see when the circuit goes open and look from there.

Something just popped into my head. There was a guy who posted a month ago who had a shorted door switch (for the interior light) He found that pretty easily.

Good luck, and welcome to the forum!

 

Hey Ard thanks for your help and suggestions, I've been doing alot of troubleshooting and testing the last few days on this and other problems with my truck. I'm pretty sure it was a bad starter relay, I changed it and she starts up perfect....before I had to let it crank a few seconds. I also read somewhere that a bad eec relay can cause your battery to go dead, so I'll keep an eye on it for the next few days to see if the relay solved the problem completely. If not, time to look at the eec.