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Headlights Flickering On & Off-High Beam Only

25K views 21 replies 6 participants last post by  Motorhead62 
#1 ·
'67 Chevelle. Start car, turn on high beam headlights, good output voltage from alternator (new during buildup), 13.8 to 14 volts constant at idle. After warm up (4 to 5 minutes) the high beams flicker on & off along with the high beam indicator in dash. Measured voltage across battery & at output terminal of alternator during flicker, still good steady 14 volts. Then put lights on low beam, no flicker no matter how long it runs at idle. Turn brights on while still warm & running, it takes about 10 seconds before the lights start to flicker again, back to dim stops the flicker. Running other power accessories or not doesn't seem to affect it, just having the high beams on & warmed up. Any ideas so far??

Thanks for your time......Odie
 
#4 ·
Thanks for the replies. I though the same thing & put a new dimmer switch on a month or so back trying to cure this & when the problem was still there I just drove using the low beams to avoid it. I'm thinking now that there might be higher & lower quality dimmer switches on the market & where I can get the best one to give it another try.
Just curious, is there a headlight relay in the original harness (the car has the original harness in it)? I found what the manual shows as the horn relay with several wires going to one terminal on it, but no headlight relay.
Thanks again for the responses.......Odie
 
#5 ·
Are the lights pulsing or going completely off? If they are going completely off have you changed the headlights to a newer high wattage style? There is no headlight relay but there is a circuit breaker built into the headlight switch.
 
#6 ·
Hi John,
Yes, the lights go completely off & on. It had been so long since I put the headlights in, I forgot that I put "Halogen" bulbs in all 4 places! I did put a new headlight switch in during the restification. Is it the circuit breaker in the switch due to the Halogens? Is there an easy recommendation other than rewiring with relays or just drop to non-halogen bulbs, etc.? Thanks for your help.
Odie
 
#8 ·
My 64 did the same thing. The halogen bulbs were overloading the headlamp switch causing the internal breaker (it is actually a bimetalic strip with a set of contacts) to open and then close when it cooled enough. Real nice on a dark country road as you enter a curve :(
The best fix would be to install relays at the lights. It will increase the voltage to the bulbs making them brighter and take the load off of the wiring and headlight switch.
 
#9 ·
Just went out & fired it up with high beams on & after a few minutes when the lights began to go off & on, I disconnected just one of the low beam bulbs & the off/on stopped with the remaining 3 lights working fine. Then I reconnected & repeated with the other low beam light & the same thing happened. I don't know if I had left it going even longer if still having one of the low beams connected would eventually cause the on/off also, but it looks like maybe more lights than the circuit can handle without relays. Does that sound right?
I can identify with the fear when the lights go off while going down the road, since another symptom that I didn't mention was that when the lights start going off & on, sometimes when I press the dimmer switch to go back to low beam & come back from the dark, the lights stay out completely for a couple seconds. That was the reason that I reacted by putting on a new dimmer switch back when that happened.
Thanks for all your help.........Odie
 
#10 ·
That is exactly the same problem I had with my 64 even switching back to dim it will take awhile for the strip to cool down and close the contacts. Installing the same type bulbs on the 70 and 72 cars no problems occured. The switches are the same except for the extra lug on the early ones but the wires on my 64 were only 20ga and on the 70/72 they are 16ga. This could possibly lead to overheating the circuit with higher amp lamps. Keep in mind from the battery to the lights with the factory wiring harness is probably more than 15' and with a couple of relays you can shorten the path to about 4' and reduce the load on the switch to less than 1 ampand increase the voltage to the bulbs by about 2v.
 
#11 ·
Just bugging you all again for more info. What gage of wire would you recommend for use from the relays to the headlight sockets (& grounds for the sockets)? Also, I'm having a little trouble finding good heavy headlight sockets to accept heavier wires to replace the stock ones. Do you have any suggestions?

Thanks......Odie
 
#12 ·
Odie the wires in the plugs and the plugs will not have to be changed if you go to relays. The advantage is in shortening the supply to the lamps. The existing wires from the dimmer to the lamp sockets will have to be cut and attached to the relays to open/close the contacts. The wire from the lamps will go to the load or output side of the relay. The input will come directly from the battery thru a 20 amp circuit breaker. This wire does not need to very large, 14ga should be enough. Since the switch now controls only the relays and the source power is less than 4' to farthest lamp voltage is increased to the lamps and load is decreased on the switch. Years ago some posted a diagram, a search would probably find it. There are kits you can buy, but buying the relays, breaker, wire and some spade connectors would be a lot less money.
 
#14 ·
Thanks for the info. I put a Painless full harness kit in my brother's street rod a couple of years ago & added relays but let someone else convince me during that experience that it needed heavier headlight sockets because it would supposedly 'arc' & burn them with the 'lighter' ones that came with the kit. I used some that I picked up at Louisville that were heavier wired & better connected because of that recommendation, but I couldn't remember who I got them from.
I'll clean the original sockets real well & spruce up all the grounds also to try to prevent problems. That really simplifies the job.

Thanks again for your help.........Odie
 
#15 ·


Try the above link. I did my headlights that way and I found the wiring dia. I made. It was for a 69. LG is light green and T is Tan. I see I have 20ga wires listed as the grounds but I'm not sure. I didn't change the wires to the headlight sockets so its all stock. I just patched in the relays R1 & R2.
 
#17 ·
Odie just do not use fuses in the circuit. As you ahve experienced when something goes wrong it is better to have intermittant lights than no lights at all.
 
#18 ·
I put the fuses in to protect the equipment and isolate any problems. The stock wiring has 1 fuse for control, low & high beams. I wired mine so you have 3 different levels of protection. 1 for control, (stock fuse), 1 for low beam and the other protects the high beams. Now if you have a problem with the low or high beam sockets or wiring, you will only lose that set of lights. Of course if its in the control side you will lose all your lights but it will narrow down where your problem is.

Newer cars have relays and fuses for each individual lights. This proves that 64elcamino hit the nail on the head when he said: (some lights are better than none). But we are not here to talk about new cars.....
 
#21 ·
Hal it auto resets in a fashion. The breaker has a fixed contact and moving contact. The moving contact is attached to a bimetalic strip. This is 2 pieces of dissimiliar metal that when heated expand at different rates. When a short or overload occurs the bimetalic strip curls and opens the contacts. When it cools it closes the contacts. The only GM switches I have are good and I didn't want to open them up. This picture is of a Ford switch. It has 2 breakers in it (cause Ford likes to complicate simple things) G and F are the strips, B and C are the contacts. A is battery power in to the assembly. D and E are resistence calibration notches cut into the arm.
 
#22 ·
I had a bad dimmer switch on my 67 cause the same thing. Changed out the switch and happy ever since. :thumbsup:
 
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