Hi guys!

Um, ok I have a unknown power drain on my battery so I unhook the Neg cable overnight...and today I went to hook the battery up and after hooking it up I jumped in the truck and went to start it and it cranked over real slow and wouldn't start so I turned the key to OFF in park and it kept trying to start- turning the starter over just as if I was turning the key!
I got out and unhooked the Batt luckily before it did start and whenever I try to hook up the Batt now it throws sparks when trying to attach the Neg cable! and most likely would try to start if I did hook it up!
1986 F150 1Barrel 4.9L all stock auto tranny

Seems like something is fused/shorting??
Please help as far as I know may be the Ignition switch itself or are there any relays, etc? It also has a wire coming off the Pos battery cable- does that go to the alternator? It has a fusible link on that wire also...

Thanks

 

Sounds like either union or Starter solenoid. There should be a solenoid in the fender next to the battery. You can jump the truck with it, if it fails in the start position, that could happen

 

I reckon best way to test that is unhook pos cable goin from sol-to-starter so it doesn't start and see if Im gettin constant 12 there at batt-to-sol?
but its throwin sparks when i try to reattch neg cable so maybe thats bad idea- will it blow up the batt cause its leaving melt marks on the neg when i try to connect it...

 

Sounds like a typical starter solenoid failure. They like to fail in the on position, the contacts stick together.

Follow your positive battery cable and it should be attached to your starter solenoid..

You might try giving it a whack with a screwdriver handle or wrench. Often that will un-stick them, for a while...

 

Thank you brothers!
Ok, putting an Ohm meter on the contacts of the pos-to-pos on the solenoid gives me 0.00 so that means its stuck together right?
I'm gonna go smack it...

 

SOLVED!

Ok, after smacking it a few times it now registers like 8.something on the ohm meter and doesn spark or try to start when I hook up neg cable.
So, the solenoid's goin out or what?

 

Yes, drive to AutoZone and get two of them, replace the one, and keep their other in a parts box behind your seat, just in case.

If I remember they are like 26$?

 

Yes.

The solenoid might work for a while but it will surely fail again.

I went through a few solenoids myself before replacing the positive battery cable with a brand new heavy one. Theory being the extra resistance caused by a bad cable (internally corroded, bad terminals, etc, etc,) will cause too much draw across the solenoid contacts and fuse them together.

I'd recommend at least replacing the positive battery cable along with the solenoid.

 

Since your there, get the tfi too! It's only a matter of time until it goes out! And then you'll have a good one and you take the bad one back on your 1yr warranty and get another back up.

Symptoms for that is, truck dies as soon as it's warm. Has fuel but not much spark.

 

You said it cranked slow. Low voltage will aggravate the sticking problem. You can buy a new one, but they are known to fail right out of the box. Keep the new one as a spare and see how long the one you have lasts. The older ones are usually better than the new ones.

 

Thanks guys!
Sorry it took awhile to respond, busy and just had to move and get new internet as well.

dylansf23 and Brnfree I have replaced the solenoid and Pos cable yesterday.
And dylansf23 yes bro I know all too well about the TFI issues! I bought a new one not long after I got the truck and it lasted 3 months before dying, so I put the old one back on and it's still working for now- will try to get a Pertronix unit or convert it to the TFI which goes on fenderwell?
Thanks

 

Damn it Jim!
Apparently it is NOT fixed!

Last night, after installing new pos cable and starter solenoid I left batt cables attached and this morning as soon as it started the solenoid again got stuck on and trying to start truck even with key-off!
Got out, disconnected neg cable, smacked solenoid a few times and now its ok but have a drained battery
What could be pulling power while the cables are attached overnight?
Noticed when I installed new solenoid it has a post for a coil wire or something? my old one had no wire connected there either?
it has factory radio which doesnt work anyway
what is the wire coming out of wiring harness and going to Pos cable head?
Thanks for any hel;p

 

So you did put a new solenoid on? A lot of them fail and stick right out of the box.

If it cranks over fine after sitting overnight, you probably do not have a drain do you?

The extra terminal is for older trucks that did not have the coil resistor bypass built into the ignition switch. These trucks have the bypass in the ign switch wiring, so they do not need this terminal unless you have a 460 with electric pumps.

 

Thanks Franklin2, yes, just installed new solenoid yesterday, kept old one, then let truck sit overnight with cables on
this morning it cranked right up but starter remained ON while engine was running- tunrned key to off and took it out and starters still trying to spin, but slowly like it's a dead battery.
as I said earlier Got out, disconnected neg cable, smacked solenoid a few times and now its ok but have a drained battery?
on meter battery usually says 12.89 or more volts when off but when trying to crank it its like its dead, slow cranking or a click
even after replacing cables and solenid its still doing this?

 

OK, so I took a multimeter and with batt cables on batt goes from 12.89 to 10.50 as soon as I put them on.
no voltage going to where starter cable is hooked to solenoid- only things hooked to where the Pos batt cable goes to solenoid is two wires one goes into a wiring harness going under motor and the other goes into a wiring harness going towards carb/firewall.
One or both of these wires is getting 12v even when truck is off so what are those two wires going to? And are they supposed to be hooked there or where the starter cable goes to solenoid?
thanks

EDIT- heres a couple pics