Hello, I have a 1986 Ford F150 300 4.9L. When I hook up the positive and negative cables on the battery it creates a big spark and it tries to turn on without the keys in the ignition. What do i do?

Asked by Jan 31, 2016 at 01:24 PM about the 1986 Ford F-150

Question type: Maintenance & Repair

I bought this truck a couple months ago knowing it has an electrical problem
and wanted to work on it. I cant find the parasitic draw or short. I have
changed the battery, alternator, starter, starter solenoid, and spark plugs. If I
leave the battery plugged it drains within a few hours.

I took it to Pepboys and they ran an electric diagnostic and they said the
alternator was bad so i replaced it. The following day I tried turning it on and it
was dead. So I took the battery to get it charged and tested. It came back and
passed the test. I went home plugged it up and turned on my truck. I let it run
for a couple minutes, and then I turned it off and tried turning it on to see what
would happen and it sounded bad so I turned it off and it kept running. I had to
unplug the battery for it to stop. Now I cant hook up my battery without it
trying to start. I have 7 out of 12 fuses blown.

I need help, any advice?

34 Answers


I would start from the starter. Remove the small wire to the starter relay mounted on the fender wall and see if it still cranks, if it does, u have a bad relay (stuck closed),if it only cranks with this wire plugged in, check the ignition switch also findout what the blown relays were feeding but don't replace them yet til u have fixed the starter issue

1 out of 1 people think this is helpful.

Okay, however I just changed the relay yesterday and the ignition switch about a month ago. What could possibly make them go bad?


Did u check it to see if it was bad or just replaced it. U want to diagnose the problem first before replacing parts otherwise u'll end up spending a lot of money and not fixing the problem

I did what Irodri911 said. I changed the starter solenoid and it fixed the problem. So that's fixed. Now to the parasitic drain....what should I check that I may have missed. If fuel gauge, oil gauge, ect, don't work. Could that pull enough draw from the battery to drain in within 4-5 hours?


Sounds like u might've left a wire disconnected at the relay or at the ignition switch

This problem existed before I bought the truck and made changes.


Did u identify and replaced the blown fuses

I did identify them...after i get off work i'm going to the auto store to buy the fuses. However there are some fuses that are not all there. Do all the slots need to have a fuse?


To check for a parasitic draw you will need a multimeter capable of reading amps and MA's. Check for the draw using the negative cable and battery ONLY. Remove the cable from the negative side and place one lead on the neg battery terminal and the other on the negative. Set meter to DC amps and check for a draw. Should not have more than about 50 MA draw. If the meter indicates a draw, begin removing the fuses, one by one, until the draw stops. That will show you which circuit is at fault and the associated parts.

When i figure out which circuit is at fault, do i change the fuse and its fixed. Or do I need to check all the wiring that the fuse has?


If the fuse still blows, you"ll have to troubleshoot that particular circuit. If it doesn't, your problem is fixed and not all slots take a fuse, if u see the base of the slot, some don't have the clips that holds the fuse

oh! okay. The diagram shows theres a fuse that should go there, but doesnt have a clip for it. What should i do?


Then I would't worry about it. The diagram probably shows something that ur truck doesn't have.

the diagram is on the cover of the fuse box though...


I would't worry about it.


No, changing the fuse will not fix the draw. You will have to find the offending piece of equipment causing the draw and repair it. On one vehicle I checked, the draw was in the glovebox light. The owner jammed so much stuff in the box he broke the light switch. Meaning it was on all the time. And just who can see a glove box on when the door is closed? Like wondering if the refrig light goes out when you close the door.

Does the battery need to be hooked up to check the fuses?


No, u can see the link inside the fuse if u don't have a ohm meter

I replaced all the fuses except for one which says its for "cluster illumin" what is that?

Also if the battery cables aren't tight to the terminals would battery charge with the alternator? Could that be a problem to the "battery drain"


Cluster is ur small dash for ur speedometer


Battery draining. Inspect all lights to make sure they're not staying on such as brake lights, dome or curtesy lights including glove box

Best Answer

The cluster fuse is out but the lights work for the speedometer, does the cluster fuse also work with the gauges as far as indicating the battery charge, if the truck is heated up or not, ect...



Okay I'll check that out. When I tried turning on the truck the solenoid started to smoke. What could that be?

Turns out the alternator wires were hooked up incorrectly, pepboys fixed it for $40 plus I have a new alternator. Thanks for everything. Ya'll have been so helpful.

I'm having problems with the tail light blinkers. They only work if the headlights are off. If the headlights are on you can barley see it blink. The front ones work perfect. I also changed the flasher and still nothing. What do I do?


Do the brake lights work?. Check to make sure u have a good ground

The break lights work perfect.


Try the emergency lights, it they work, u probably have a bad clock spring, it gies inside the steering column. Do u have any warning lights on the dash


Oh byt u said the front ones do work normal, so that wouldn't be the clock spring. Most likely a missing ir bad ground wire

Oh ok. I'll check that. Thank you. Also how about this... When I turn my truck on it fires up, but once I put it in drive or reverse sometimes the engine just cuts off. Even when I'm idling at a stop sign. What should I check?

Could it be cause there's a leak in the radiator hose?


Unless it's getting hot but sounds like u have a vacuum leak. Check vacuum hoses for cracks or disconnected. Sparay quick start around the vacuum hose, if engine idle changes, it's leaking around that area

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