Dim headlights on low beam and relays

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ES 1800

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I'm trying to track down this problem: (73 3.0CS)

On low beam, the headlights are very dim. But when I swtich to high beam, both the high beams and low beams are as bright as they should be.

Any ideas?

There are two cylindrical relays portside of the battery. Can someone tell me what these are? Back from them is the voltage regulator.

I have no fog lights on front.
 
If you have a US car the high beams on both H1 and H4 headlights go through a relay, while the low beams are a different filament with no relay. Dim low beams can be due to resistance in the 12 V path. The ground is probably not the issue because it is taken from the same place for high and low beams.

Incidentally there are two switches in the 12V low beam light path, the light switch itself and the headlight switch/flasher. Either the switch contacts or connectors can be the issue.

The round relays on the side are the headlight high beams and horn.
 
Check the ground wires (one on each side). There are a number of wires that come together near each front fender. You can access the wires through the cover plates above the headlights. They should be brown. Remove the screw and clean the wire tabs.

Sven
 
Those old round relays must have passed their use-by date by now. I'd replace them with new fused ones. My pre-73 coupe already had a high beam relay as standard and I added a relay to my low beam circuit, using the convenient fog light relay location. The switches and wiring are getting old, so it seemed best to take the load off them. The new relays carry their own 25amp fuses as disaster insurance. Safe for a total of 200-250 watts, but not for four uprated high beams.

Because I have H1 highs (100w), and H4 low/high outers, (80/100) - they came like that from the donor wreck - and didn't want to overload any wiring, I have a relay on each H4, which defaults to the low beam, and switches the H4 to high when the H1 comes on. That way the high beam circuit doesn't have to carry four lights- the low beam circuit powers the H4 high beam.

Daniel Stern's suggestion of wiring things so that you can use the H4 high without the H1 in consideration for other drivers seems a good idea
 
Those old round relays must have passed their use-by date by now. I'd replace them with new fused ones. My pre-73 coupe already had a high beam relay as standard and I added a relay to my low beam circuit, using the convenient fog light relay location. The switches and wiring are getting old, so it seemed best to take the load off them. The new relays carry their own 25amp fuses as disaster insurance. Safe for a total of 200-250 watts, but not for four uprated high beams.

Because I have H1 highs (100w), and H4 low/high outers, (80/100) - they came like that from the donor wreck - and didn't want to overload any wiring, I have a relay on each H4, which defaults to the low beam, and switches the H4 to high when the H1 comes on. That way the high beam circuit doesn't have to carry four lights- the low beam circuit powers the H4 high beam.

Daniel Stern's suggestion of wiring things so that you can use the H4 high without the H1 in consideration for other drivers seems a good idea
 
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