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Headlights dip when brakes applied
https://www.slantsix.org/forum/viewtopic.php?t=25708		 Page 1 of 1
Author:  bwhitejr [ Tue Nov 06, 2007 3:56 am ]
Post subject:  Headlights dip when brakes applied
When I step on the brakes with the headlights on, my headlights dip for a split second, but recover. This is a 1980 D-150 pickup.


bwhitejr
Author:  Pierre [ Tue Nov 06, 2007 4:06 am ]
Post subject: 
Power brakes? If booster is leaky it may cause screwy things to happen with engine vacuum when brakes are applied, causing rpm to vary and alternator output to fluctuate.
Author:  bwhitejr [ Tue Nov 06, 2007 4:16 am ]
Post subject:  Headlights dip
No power brakes, just regular brakes. I just wonder if it is inherant in the design or there is an underlying problem. Like a bad ground.

bwhitejr
Author:  Pierre [ Tue Nov 06, 2007 4:28 am ]
Post subject: 
Hm well the problem could be purely electrical then, when the added load of the brake lights comes on a faulty regulator takes time to "catch up" with the load? What about when you signal, headlights ok then?

Its not part of the design, I never had this happen to me when I was running the stock charging system.
Author:  SlantSixDan [ Tue Nov 06, 2007 8:52 am ]
Post subject: 
These vehicles had extremely marginal wiring when brand new, and science has yet to give us the wiring that improves with age. Put in headlamp relays and not only will the headlamps quit blinking when you step on the brakes, they'll also get much brighter.
Author:  LUCKY13 [ Tue Nov 06, 2007 10:45 am ]
Post subject: 
Thats a very good idea Dan, I didnt read that hole artical but I do knwo that the wiring running to the headlights is like a risistance wire also. This cuts the voltage down to where the headlights are not as bright. That has nothing to do with lights droping when other loads are applied but it helps to have better lights itself.


As far as the lights droping when brakes applied, I expect either the voltage is very low at idle and can't hold the load. Or maybe there is a ground problem causing some flucuations. Be sure the is a ground strap from the engine to the body of the car. And from the batter to the body of the car Also be sure the belt that drives the alternator is tight and not slipping. Then take a voltage meter and check the voltage of the system & get someone to help you. Let your helper put the car in gear with the lights on & check to see how much voltage it holds.


Many times the factory system is very limited like Dan said. A upgrade is the best option, either the newer style regulator, or even a better alternator alltogether that has a built in regulator. But even with a upgrade system the car needs good grounds to function right so do the checks and repairs on this area first.


The relay system is a veruy good idea even if all has been repaired and working good. The lights are much mroe stable even if other problems persist and you get much bright lights that when upgraded to newer style light bulbs themself can give lighting compaired to newer cars. The older I get the more I find the need for this myself. Just last night I was driving my 68 Cuda in the rain, I seen very quick that I need upgrades myself & my system is working fine.


Jess
Author:  SlantSixDan [ Tue Nov 06, 2007 11:01 am ]
Post subject: 
Quote:
That has nothing to do with lights droping when other loads are applied
It actually could, depending on the condition of the connections at the firewall pass-through junction block and under the dash.
Quote:
Be sure the is a ground strap from the engine to the body of the car. And from the batter to the body of the car
Good idea, but that is usually not enough with old vehicles, because it still relies on sheetmetal grounds. Run a 14ga ground wire from the "GRD" hole on the alternator to the regulator base, and from the regulator base to battery negative.
Quote:
the newer style regulator
...is already present on this post-'71 truck. :-) That does not necessarily mean the regulator on this truck is working as well as it should.
Quote:
a better alternator alltogether that has a built in regulator
Alternators with built-in regulators are not necessarily better.
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