Edit; I have a '65 Coupe

I posted about this probably 7-8 months ago but because I went to college and left my mustang at home, I didn't bother asking about it. Now that I am back, I'm really trying to fix this so I can use the car as my daily driver instead of just daytime driver.

Four days I had just got done taking the dash out and switching out the headlight switch because that's what most people said back when I posted about this problem months ago. I turn her on, drive around all day and then take her out at night for about 30 minutes. Magic! They worked! I thought I had fixed the problem. Two nights ago, I was driving home from my girlfriends house at around 2am and my headlights go out on the freeway, flickering off and on. It was a lot of fun. I even passed a cop.. funny he didn't stop me. Anyway, now that I think about it, after sitting for 8 months the battery was pretty much dead.. so I spent an entire day charging it up.. so maybe they worked because the battery was fresh? Any other ideas? Headlight switch is not the answer.. and my father said it could be the selenoid (he's a Chevy dude and mocks my attempts at working with a Ford).. and after rehooking up the dash, the alternator light is permanently on when I turn the dashboard lights on. Could the alternator have something to do with it? When the car is off, the battery runs at 13/w or whatever the **** I'm measuring but when the car is on, it jumps to 15/w and I know that is not normal.. so could the battery be at fault?

.. Lol, k, so that's a lot of questions. If you take anything away from this, take away that I am completely ****ing clueless. Any help would be much appreciated! Thanks!

 

Sounds like you missed hooking up a ground wire somewhere in that dash.

 

It.. was happening before I took out the dash.

 

Oh, in that case, you may want to have your alternator tested. It may have bad diodes. Your voltages seem a bit high too. 13v?

 

The headlight system in these classic Mustangs is fairly simple.

Switch

Dimmer switch (on the floor)

Wiring in between the switch, dimmer switch and the headlights.

Yes, your battery reading 13 volts while the car is off is fine.

Yes, your battery reading 15 volts while the car is running is fine (the alternator is causing this as it's running the car and re-charging the battery).

Do you have an aftermarket stereo installed? Maybe something with an amplifier that is sucking power? The original alternators were not designed to provide enough amperage to support a lot of external devices.

Halogen headlights or original type sealed beam units? Halogen headlights will pull more amerage through the switch. This can cause some switches to overheat and temporarily shut-down (until they cool off). An old trick was to use a headlight switch from a Mercury Cougar as the Cougar switches were built to handle a higher load.

If it were me.... I'd start with the switch and usethe one spec'ed for the Cougar. IIRC, it was the 1968 model, but I can't be certain of this.

If the switch checks out okay, consider a headlight relay kit. NPD, and other suppliers carry these. I like the one built by Scott Drake as it's a plug and play type addition. The relays will pull power for the headlights directly from the starter solenoid.

Good Luck!
Dave

 

Sadly.. I have no aftermarket stereo, I have standard original type sealed beam headlights, and I just replaced the switch. Haha.. I am going to go through the wireharness that looks like it was replaced by the previous owner and see if anything is weird with it.

 

Did the dash lights blink along with the headlamps ???

If so look under the dash for an issue. If not try looking at the harness from the firewall to the headlamps and then the grounds.

FWIW.