TD's 64

Good morning folks,
I am restoring my '64 roadster and my inboard high beams are dim. Outboard low beams are full brightness. I have replaced the headlight switch and the dimmer switch and the harness from the firewall forward is new. I appear to have 12 volts getting to the lights but notice the lamps are 50W where the originals appear to have been 37.5W. Could this be the source of the problem? Also, the manual says the headlights are protected by a circuit breaker. Does anyone know where this would be?

Thanks, Tom

Tooth Doctor

The circuit breaker is in the headlight switch. Check the ground to your headlights, run a jumper wire to a known good ground, if they get brighter that's the problem. I don't think the wattage of the lights is the cause.

TD's 64

Thank you Tooth Doctor. Will check tonight

SDVette

Perhaps the low beams are Halogens? And the high beams are incandescent?

65GGvert

If your description is accurate, the wattage, headlight switch, dimmer switch, circuit breaker, and wiring have nothing to do with it. If when your brights are on the two outside lights (dim) are brighter than the brights, you either have bad ground connections at the bright bulbs, or you have dimmer bulbs like SDVette said. I put a halogen in one of my brights and had to change the other from the T3 stock bulb because the halogen was about twice as bright as the original.
If on the other hand, all four lights aren't coming on when bright is selected, we need to talk further about the possibilities. When on bright, the 12v feeds directly from the dim to the bright bulb on both sides, using the same ground, so it would have to be something really funky to have both brights dimmer due to a bad ground. My opinion is that you need to put halogen bulbs in the bright positions.

TD's 64

I cleaned the ground at the radiator shroud and got no improvement. The lights are stock T3s so it is not a halogen issue and when I say dim, the filaments are just glowing. I will try the ground jumper idea to see if I am missing anything. Seems unlikely given that everything else on that ground circuit is operating well. Perhaps a short on the wires coming from the dimmer switch?

65GGvert

It won't be a short. The filaments are all fed by the same voltage. On dim, the 12v goes to one of the two filaments in both sides dim bulbs via the tan wire. On bright, the same 12v is fed on a dark green wire to the other filament in the dim bulb and the only filament in the bright bulbs on both sides. So if the dim bulb is ok on dim and also on bright, the only difference is the bright bulb, or the short wire and connector that feeds from the dim bulb over to the bright. For both brights to be dim because of a problem on both sides that is identical is not likely. If your dim bulb drops in brightness when you switch to bright, then you could have a problem in the connector at the firewall, or at the dimmer, or the contacts in the dimmer could be corroded. If the dims stay good and the brights are dim, it's the bulbs that are weak. If you measure voltage on the dark green wire, you should get near battery voltage. If you do, you need to sub in a bulb in the bright to verify a bad bulb. You can use an H5001 halogen bulb for the brights from any parts store for around 10 bucks apiece and they will be twice as bright as the T3's. If you want T3's you'll have to pay considerably more.

Maybe it just your terminology for a bad connection, but a short would cause excessive current and more problems than dim brights.

TD's 64

Thanks for your thoughtful response.

65GGvert

Did you find the problem?

65GGvert

I'm posting to bump this back to the top. I don't think you're one of those types that ask for help, and then don't post the resolution. I just want to find out what the problem was for future questions.

TD's 64

I will certainly share my solution, though I expect it will be embarrassing when it is found. I cleaned the connections at the dimmer switch last night and they were pretty crusty. I was sure that would solve the problem but no joy. I did confirm that even the low beam outboard lamp dims somewhat when the high beams are on (which still barely glow). I tested the inboard high beams out of the car and they work. I am thinking I might replace the female terminals at the dimmer switch this weekend in case corrosion has worked into the copper wire adjacent to the switch. I plan to also test voltage at the firewall terminal and recheck the voltage at the lamps. I will also follow up on your suggestion to jump the ground to a known good source. Thanks for your attention and help. Tom

65GGvert

It's not ever embarrassing to find a problem and resolve it. If they work out of the car, you're down to 12v or ground. You can also jump from the input wire on the dimmer (light blue) to the dark green on the output side to eliminate the dimmer as a problem. After all you've done, it sounds like the problem is going to be around the dimmer or the connection. Remember, you also have that connection (dark green wire) passing through the outboard plug on the firewall below the master cylinder. It could be corroded or loose there as well.

Frankie the Fink

The problem is that our 50 year old wiring harnesses get "black corrosion" internally and you can't readily see it, but it degrades the wire's current carrying capability.

Mad Electric waxes eloquent on this in their article: http://www.madelectrical.com/electri...adlights.shtml

Note that a 10% drop in voltage delivered to a bulb can reduce illumination by 30%...

leif.anderson93

...on a bulb that barely illuminates to begin with even with everything working 100%

TD's 64

Very nice article. Before I decided to restore this car, I had installed H4 Hella high performance lamps and the associated relay system described by Mad Electric. Unfortunately, the Hellas disappeared (along with many other parts) at the shop I hired to restore the car (I eventually fired them and took the car home in a million tiny pieces to do the restoration myself). In my desire to do a stock restoration, I went back to the T3s and the original wiring schematic. At this point, I think I will install relays for the T3s and bring a dedicated 12V power source from the horn relay. Perhaps I will hide the relays in the headlight buckets to keep that stock look.

I will report back on Monday how things went. Thank you all for your help and expertise and have a great weekend. Tom

tbarb

Have you used a voltmeter to see if there is 12 volts at the headlight plug and maybe work backwards.

TD's 64

Yes, but I will recheck before I rewire. THanks

tbarb

The low beam has a ground and two power terminals and the high beam has a power and ground. Use the ground and see if battery voltage is present, if not use a known good remote ground and check the voltage.

Trouble shoot from there, it's possible the plug has corrosion and you may save lots of work and $$$

Ironcross

If you want brights that are really bright get yourself a set of 4537 Aircraft landing lites...As I mentioned, instant daylite

Photobucket has not been very good for me,...trying to get my 62`s headlite picture up....no luck

TD's 64

Well the mystery of the dim headlights is solved. After installing relays and still not having a resolution, I began testing continuity from the headlight switch forward and low and behold, the plugs for the headlight harness extensions were wired wrong by the manufacturer and did not match the pattern on the main harness.

High beams were energizing the low beams, low beams were energizing the ground and the ground was grounding the high beams. I can't decide if this is a prank by a Chinese factory worker or one of gross incompetence (both on my part and on that of the vendor) but the lesson is, never assume the repops you buy are correct. Given the number of threads that parallel this discussion, one wonders how many of these parts are in circulation.

On the bright side, (pun intended) I now know all there is to know about headlight wiring and my 51 year old dash harness has one less load to shoulder. Thank all of you for your help. Tom