Electrical Halogen Headlights

Discussion in 'Classic Mustang Specific Tech' started by candphall, Jul 2, 2013.

  1. Are halogen lights typically dimmer than the original sealed beams when installed in the existing system?
  2. They certainly will be, when they either start flashing off and on (every few seconds) or go out completely when you install them without a relay setup. The small gauge OEM wire (now with more resistance after 35+ years) and the OEM switch were not designed for the extra amperage drawn by halogen bulbs. The wire and switch barely accommodate the original, style lamps. A relay setup is easy and can be done in a very sanitary manner. The one from LMC Truck is OK, but I like to make my own with heavier gauge wire.


    I know it's listed for trucks, but it's the same as you need for your car. Plug and Play.

    Also, all grounds should be checked and confirmed.
    My $.02,
  3. I've been running halogen 7" sealed beams in my 66 for many years, with no problems. Nice and bright, too. It helps if your wiring is in good condition, and I like to keep the connectors pristine with a little silicone grease in them. Some people like to use a 69 headlight switch to add a little capacity, but I haven't needed to do that. If you really worry about this, there's a ready to use plug-in relay kit for you. Glazier/Nolan calls it G09558.
  4. halogen headlights are typically brighter than incandescent bulbs are. if yours are dimmer then you have an issue, likely a bad ground in the system.
  5. This is what I found , the car has been totally rewired , the voltage out of the headlight harness is 12.30 volts. When I plug in the headlight extensions the voltage drops to 11.58 volts at the bulbs. I am attributing the voltage drop to old extensions which I have not replaced. Hence the dim lights. Am I thinking correctly. I would like a second opinion before replacing the extensions. The only thing I find odd is the voltage a drop is identical on both sides.
  6. again, it sounds like bad grounds. if you are testing the power to the headlights with a probe that is properly grounded, and you have proper voltage to the headlights, but when you plug the lights in and your power drops off, you can suspect bad grounds just about every time.
  7. agree with checking the grounds, first.

    also what gauge wire are you using to power the beams? On my lights I used a relay setup, with the wires that came with the wiring harness to signal the relays (which have a large gauge wire in and out for power).
  8. Have you tested voltage drop like I described in the other thread? That will pinpoint exactly where the problem is.
  9. I value you input 66coupe but I have been on the road for the last several weeks and have not had an opportunity to do the diagnosis you described. But it's on the list, may be next week I will keep you posted.
  10. Tested per 68s diagram and found the dimmer switch the problem. Replace and everything is working and bright.
    Iamdiffrnt likes this.
  11. i have had those fail before. good find.