Why car wont start if the headlights are on?

Answer 1

most likely cause is the alternator not charging correctly. normal charge voltage with all accesories on is around 13 to 14 volts.anything less than 13 volts means that your alternator isn't charging and the car runs off of the battery until it can't run anymore. As the voltage drops, there is less power to produce a spark and the spark gets weaker or disappears until it can no longer ingnite the fuel/air mixture. You will probably notice that the top speed you can go keeps dropping as the battery drains. When it stalls you will not be able to get it to crank again without charging it.

Answer 2

#1) BLOWN FUSIBLE LINK under the hood (usually near battery or alternator) Sometimes this is a special kind of wire that's about 6 inches long and spliced into the circuit; and you may not be able to tell it's blown just by looking at it requires testing with meter or test lamp. You would need to look up the correct replacement in a repair manual and replace/splice where the old one was. Maybe a half hour labor, the part SHOULD cost a couple of dollars but sometimes dealership markup is AWFUL, maybe twenty bucks. Most modern cars have a JUNCTION BOX (like a fuse box) under the hood, usually near the battery. The fusible links in here are more like a fuse, usually have a window so you can see if it's blown. These are more of a do it yourself item to replace, they're labelled with their rating (30A, 45A, 60A, etc.) Costing two or three dollars.

#2) possible bad relay, I would suspect the ACCESSORY circuit. Someone who knew what he was doing could test with meter or test light. Half an hour labor for the mechanic, I've seen the part as cheap as five bucks on eBay for a generic relay, but a special order item could be more. It would bother me to pay more than twenty five for the part unless it was for a vehicle with A LOT of high power accessories.

#3) bad ignition switch

#4) possible broken or disconnected wire these can be a MAJOR pain to track down, but with everything out but start and headlights (maybe horn? or emergency flashers?) it narrows things down quite a bit.

#s 1,2 and probably 3 I would expect any garage could handle, but if these were eliminated I'd consider taking the car to the dealership for #4, because familiarity with the make and model could make a huge difference in cost of repair.

good luck!

Answer 3

hopefully it is just your terminals, check and clean, check startermotor, check coil, check points, check all starter compoinits and wiring.

Answer 4

Battery is probably old or weak or too small for the vehicle, having the lights on would drain on the battery affecting its overall cranking amps

Answer 5

Battery is dead or unplugged...