Left the ignition switch on in my car for 2 hours. Please help.

Wait, I'm confused... why would you turn off the "good" car before you tried to start the "bad" car?

And what do you mean by "ON" position -- do you mean that the car was running for two hours, that it was in accessory (car not running but battery powering the radio and lights and so on), or that it was in the ignition position (where the starter is trying to start the engine... but I can't imagine you held it in that position for two hours )?

Connect the cables - live positive to dead positive, live negative to dead ground.

Start live car.

Start dead car.

Remove cables in reverse order as above. Try not to let the ends of the cables touch as bad things can happen.

Take jumped car and drive around for half an hour or so.

Uh, keep the "good" car running WHILE you crank the "dead" car. You are jump starting the dead car, not recharging its battery. The "dead" car, once started, recharges its own battery via the alternator/generator while you drive around.

mkrishnan said:

Wait, I'm confused... why would you turn off the "good" car before you tried to start the "bad" car?

And what do you mean by "ON" position -- do you mean that the car was running for two hours, that it was in accessory (car not running but battery powering the radio and lights and so on), or that it was in the ignition position (where the starter is trying to start the engine... but I can't imagine you held it in that position for two hours )?

Click to expand...

It's actually safer for the "good" car to jump that way (turn off the good car), but I've found through experience that it usually doesn't get the battery charged enough to help the car to start.

I think he left it in the "on" position, right before "start," which means his a/c fan could run and everything else. Hard to believe someone would accidentally do that though.

Anyway, OP, do what the other poster said and jump the car while the good car is running. I would think your battery is fine and just needs a charge.

The negative jumper cable should NOT be connected to the negative terminal on the dead battery, it should be connected to a metal part on the engine block, safer that way.

Also, I used to have an '85 Ford Escort that generally couldn't be jumped by another car. A wrecker driver, who was able to jump it with his wrecker, told me it was because the Escort used a high amperage battery and most other cars didn't have the power to jump it.

I like to keep a standalone car battery charger in the house. I think I picked it up at the Home Depot, and it's been useful for car batteries and my lawn mower's battery as well. The nice thing is that you can leave your car plugged into AC (through the charger) without having to waste a half hour driving to charge the dead battery.

definitely leave that puppy running so it will charge and if it dies again there may be other issues as well, check to make sure the jump starting didn't fry your alternator or the voltage regulator too. Its simple just leave the vehicle running and disconnect the battery at either terminal if the car stops running the moment you unhook the batt from the electrical system your alt or your regulator is fried and you might be running off the juice from your battery alone which is a very bad thing and can leave you stranded.

Well chances are good that the jumper cables you used were crap and did not have a thick enough gage. This means that it charges the other battery a lot more slowly and less amps can be pull of the car providing the power for the jump start.

I have learned this threw multiple jump starts off cars with completely dead batteries. Let my car die once tried to jump with my crappy cables off a friends car and did not work and slowly charged. We pulled out his nice cables and hook them up and you heard his engine have to deal with the draw to charge my bat. Still took about 10 min for my battery in my car to be able to start with the help of his truck running.
I had the same thing happen when I was jump starting some guys truck. He had crappy cables and we could not get it to turn over. I pulled out my nice cables and took about 5 min to get his bat with enough juice to turn the car over with the aid of my car.

Rodimus Prime said:

Well chances are good that the jumper cables you used were crap and did not have a thick enough gage. This means that it charges the other battery a lot more slowly and less amps can be pull of the car providing the power for the jump start.

I have learned this threw multiple jump starts off cars with completely dead batteries. Let my car die once tried to jump with my crappy cables off a friends car and did not work and slowly charged. We pulled out his nice cables and hook them up and you heard his engine have to deal with the draw to charge my bat. Still took about 10 min for my battery in my car to be able to start with the help of his truck running.
I had the same thing happen when I was jump starting some guys truck. He had crappy cables and we could not get it to turn over. I pulled out my nice cables and took about 5 min to get his bat with enough juice to turn the car over with the aid of my car.

Click to expand...

Agreed I always invest a few extra bucks in the good cables myself

......so Rodimus I have to ask, when you're in robot mode where do you hook the jumper cables to? LOL

DewGuy1999 said:

The negative jumper cable should NOT be connected to the negative terminal on the dead battery, it should be connected to a metal part on the engine block, safer that way.

Click to expand...

I've heard that but I've never been able to get that to work when jump starting any car. It's the first thing I try and it has failed every time so far. Jumping from both terminals works a charm every time.

Just let it sit over night and try to jump it in the AM. Sometimes my car wont crank when its too cold.

Leaving the key in on spot does no damage to the engine. It sounds like crap jumper cables. Chance are good you battery is completely dead. Go get a charger for you car and charge the battery best way to do it as the car alternater is not design to charge a dead battery any how. It is designed to run the car and to recharge what it took to start the car.

How fast is the engine cranking over. Because it sounds like you do not have enough power to throw a spark and run the starter

guitargoddsjm said:

I like to keep a standalone car battery charger in the house. I think I picked it up at the Home Depot, and it's been useful for car batteries and my lawn mower's battery as well. The nice thing is that you can leave your car plugged into AC (through the charger) without having to waste a half hour driving to charge the dead battery.

Click to expand...

I got one of these also, actually, after I had the battery die on my 6 after not driving it for a couple weeks... it turned out that the death was due to corrosion build-up on the battery, but then as it turned out, the battery died permanently a few days later, and I've actually yet to use my charger.

Most consumer jump leads are crap,if you can borrow another set and double them up,or try and borrow a decent set.You lucky the Willeys doesn't have the original engine standard practice to start them in cold weather involved lighting a fire under the inlet manifold.

If you want to make yourself some decent jumpers get a length of 500 amp welding cable and four welding clips.

Does it even turn over?

OK I want to know since everyone else has clearly helped best they can ... wtf were you doing where you "accidentally" left the ignition on? Honestly, I thought of waiting for someone, being out on a date (you can fill in the blanks there), or you're really dense.

Just push start it. You know how to do that don't you?

Idling the good car is not always enough. Better to run it at 1,500 RPM or so to generate the additional power required, and let it run longer while connected. If it's a 1945 Jeep, you may find that it's positive earth, not negative. Are you sure you have it connected the right way round?

I believe the original 1945 Jeep Willys MBs all used a 6 volt battery and electrical system with negative ground rather than the 12 volt batteries found on most "modern" vehicles. Check your battery -- it should indicate the voltage somewhere on the battery. Conversions to 12 volts are commonly found however -- and some old Jeeps conversions use both 6 volt and 12 volt components. You really should find out what you've got before you precede...

In general, 6 volt auto batteries don't have a lot of reserve power and they were always (too) easy to drain down to the point of the vehicle not starting. Jump-starting a vehicle with a (completely dead) 6 volt battery from a "modern" 12 volt vehicle can be difficult with wimpy battery cables and connecting 12v worth of juice to a 6v system could fry the (6 volt) electronic equipment on your Jeep -- turn off radios, heater fans, lights, etc. on the Jeep -- and disconnect the 12 volt jump ASAP after the 6 v. vehicle starts -- if you get a good* connection to a 12 v battery your 6 v starter on the Jeep should turn over faster than normal and (baring other problems) the Jeep should start quickly.

Leaving a 12v battery connected (jumped) to a 6v battery, either with the 12v vehicle running or with it off, for very long can be very dangerous -- an overcharged battery can explode, spewing battery acid everywhere, etc. Be careful! Battery acid will quickly eat into flesh and you don't want to get any in your eyes. I've owned over a dozen old 6v vehicles and I've never had any desire to press my luck past about 60 seconds worth of "jump". Again, unless you have other problems the Jeep should start up quickly. Probably the most common "mistake" made by people not very familiar with how to start a '45 era vehicle is flooding the engine due to excessive pumping of the pedal and/or misuse of the vehicle's (manual) choke. On the other hand most vehicles from this era do need to be "primed" to start -- the gas would drain out of the original style carburetors overnight on almost all vehicles from this era. One would normally have to close the choke and pump the pedal a couple of times while cranking the engine to get them to start "cold". But then part of the "fun" of running an ancient vehicle is learning the right "combination" it takes to get the damn thing to start.

If you do have a 6 v battery, get a battery charger that's switchable to 6-volts, etc.

THX1139 said:

Just push start it. You know how to do that don't you?

Click to expand...

I'm not 100% sure about this but I read somewhere that it's bad to push start a petrol car, it can cause serious damage to the catalytic converter.

NATO said:

I'm not 100% sure about this but I read somewhere that it's bad to push start a petrol car, it can cause serious damage to the catalytic converter.

Click to expand...

Wrong.
And I'm not sure a 1945 Willys even HAS a catalytic converter.