4.6L (1996-2004 Modular) Mustang Technical discussions on 1996-2004 4.6 Liter Modular Motors (2V and 4V) within.

no highbeams,parking,or tail lights

Old 12-01-2013, 04:43 PM
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Default no highbeams,parking,or tail lights

ok back in the spring I was driving my car and went to get on it and boom all my lights get super bright then just go out. altenator light comes on and I limp home 1/4 mile, shut the car off and wont start back

battery was showing 3 volts with the cable on and 12 volts with the negative disconnected. so im guessing a short

Figured out that when I took the big50amp fuse out under the hood for lights there was no more draw on the battery

took altenator in and had it checked, failed. put new altenator in and started the car with the 50amp out and had no problems just no lights lol

put the 50amp fuse in it today just to messing around and the battery stayed up at 12.8 volts. no draw

everything works except highbeams, parking lights, taillight and interior lights, all inside and outside fuses are good.

im guess the altenator regulator went out and sent to much power to everything and zapped it,

Where should I start? maybe the headlight switch? hate electrical!
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Old 12-07-2013, 12:46 PM
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Old 12-08-2013, 03:49 PM
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Since all those circuits have different grounds, its unlikely that its a bad ground problem. So the problem is most likely on the power side. The headlight circuit is fairly simple. If memory serves, it goes from the battery, through a fuse, to the main light switch, to the multi-function lever/switch in the steering column, to a fuse, to the headlight and then to ground. There are a total of three fuses in the headlight circuit (one for each headlight and one for the switches). Key On, Engine Off, make sure that they all have 12 volts. After that, I would go to the main headlight switch and make sure it is getting 12 volts. Then I would test the multi-function lever/switch in the steering column for 12 volts.

If memory serves, there is a module on the high-beam side of the headlight to cut out the fog lights (if equiped) while the high beams are on. It should be in-between the headlight fuse and the headlight itself.

I’d advise getting the electrical service manual for your year/model ride to get the circuit diagrams so you know which wire is which etc. You could also subscribe to, pay their subscription fee, and get the diagrams that way.
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