Pulsating lights? What would cause this?

[yellow400ex05]

The headlights on my 1958 apache start to pulsate at night, a few seconds after the truck starts running. The truck does have an alternator on it. Could it not be putting out enough current? The original gauge reads just below the center dot. When the lights pulsate all of them do it including the dash lights.

[mr48chev]

It sounds like the cut out relay in the regulator is cutting in and out.

Is this just at an idle or while driving down the road at say 45 or 50 mph?

Generators are cute and "original" and sometimes it's desirable to run one so everything looks correct but the downfall is that they don't charge worth squat at and idle.

On cruise nights you can tell the guys with generators because the lights go dim when they are at an idle and get brighter as the vehicle speeds up and the generator comes up to full charging ability.

I haven't had a generator on anything I've owned since 1973 when I traded my 59 ElCamino off but one project I have will get one because it would be all wrong looking with an alternator. If i.t goes over 100 miles from the house it will most likely be on a trailer behind the 48 or my 71 as it isn't a distance driver by any stretch of the imagination

[yellow400ex05]

Originally Posted by mr48chev

It sounds like the cut out relay in the regulator is cutting in and out.

Is this just at an idle or while driving down the road at say 45 or 50 mph?

Generators are cute and "original" and sometimes it's desirable to run one so everything looks correct but the downfall is that they don't charge worth squat at and idle.

On cruise nights you can tell the guys with generators because the lights go dim when they are at an idle and get brighter as the vehicle speeds up and the generator comes up to full charging ability.

I haven't had a generator on anything I've owned since 1973 when I traded my 59 ElCamino off but one project I have will get one because it would be all wrong looking with an alternator. If i.t goes over 100 miles from the house it will most likely be on a trailer behind the 48 or my 71 as it isn't a distance driver by any stretch of the imagination

I've got an alternator on my truck and yes the lights will pulsate when driving down the road.

[mr48chev]

Boy howdy, I need to clean my glasses. I was sure that said that it does not have an alternator.

Have you taken the alternator into an automotive electrical shop and had it properly tested? It may have a bad diode or a bad connection in it.

A bit of an explanation on how the diodes convert AC current to DC current and also somewhat of a clue to your problem with the pulsating current.
http://alternatorparts.com/understan...ternators.html

[OrrieG]

Aliens are coming after you...

[yellow400ex05]

anybody else ever have this problem? have any advice? what if my alternator tested fine?

[nvrdone]

Did this happen with a previous alternator or generator? I would have the alternator checked but also check the mounting of the alternator. If its not tight you may have a bad ground.

[joedoh]

you need either more load or more battery, the pulsating is the rectifier switching and making DC output. Headlights are a high current draw, and the alternator is an AC generator, the battery is intended to "stiffen" the output. Do you have your headlight relays wired straight to the alternator? If so, wire them to the battery, it should improve your pulsating.

[_Ogre]

pulsating? as in turn off and on?

if they are actually turning on and off rapidly then the problem is your headlight switch
the stock 55-59 wiring harness had 3 or 4 fuses in the whole system, none for the lights, the switch hooks directly to the battery
looking at this picture of the headlight switch, the batt connection has a U-shaped bar
off that U-bar are 2 sets of ''points'' these are bi-metal overloads, when power goes thru the metal strips they heat up like a thermostat
too much power or as they wear out the over current causes the points to break turning the lights off
once the points break the strip cools down the lights turn back on and the cycle gets repeated
it is set up this way to protect your wiring, but also keep your lights on in case your approaching a curve as they overload

if you have stock headlights and wiring you can tweak the strip just a bit to be a little less sensitive
this is your only wiring protection, if you over tweak you can burn up your harness
if you have a new wiring harness it should have a breaker on the headlights, you can bend the strip so it never opens the points

[yellow400ex05]

no the lights are not flashing on and off. they're pulsating, brighter and dimmer slightly, at a somewhat rapid pace.

[_Ogre]

then store my post in your noggin for future reference

how big is your alternator and what loads do you have?
electric fan, ac, halogen lights?

[yellow400ex05]

charging system checked out okay, 14.25 volts with no load, 14.57 volts under a load. 12 volts cranking.

no electric fan, radio doesnt work. i dont believe the truck has halogen headlights.

[Russell Ashley]

Early alternators had an external regulator while later ones had an internal regulator (three wire) or one wire. Which style do you have?

[yellow400ex05]

3 wire i believe, one snap in plug and a plug that has a rubber boot over it both run towards the firewall.




grounds

[OrrieG]

quick search on the internet, because I do not know why, shows it is probably the alternator diode, or battery going fubar or overloaded. You have eliminated #2 so I'd spend $30 on a new 63amp alternator and see what happens. I thought everyone was like me and had a couple just laying around??

[mgchevyparts]

Originally Posted by OrrieG

quick search on the internet, because I do not know why, shows it is probably the alternator diode, or battery going fubar or overloaded. You have eliminated #2 so I'd spend $30 on a new 63amp alternator and see what happens. I thought everyone was like me and had a couple just laying around??

X2
Alternators are cheap. Just replace it.

[yellow400ex05]

Originally Posted by mgchevyparts

X2
Alternators are cheap. Just replace it.

I think I'll try that and see if that fixes it, its only had 13k miles put on the truck since 1996. I did notice the AMP gauge at idle in gear tends to drop as the lights surge, and when your driving down the road the lights pulsate more rapidly than at an idle. can an alternator test that its charging good, but be bad?

also here's a picture of the gauge when no lights are on at an idle in park.
you can see that its just a hair below the center dot without the lights on.


and here's the gauge after the lights are on, in gear. I would think its a bit low wouldn't you say?

[47 Fasttoys]

I would start by readdressing that ground connection. I hope that's not the only one. You need a 2 gauge or better from the engine to frame and at least 8 gauge from engine to body. The one shown looks to be the right size but the wire at the ring splice looks weak.
Good luck, Rob

[Highsider]

Just mentioning that I am real happy with the 94-amp alt I bought for $75 at O'Reilly's.

http://www.oreillyauto.com/site/c/de...eyword=01-1015

[_Ogre]

Originally Posted by 47 Fasttoys

I would start by readdressing that ground connection. I hope that's not the only one. You need a 2 gauge or better from the engine to frame and at least 8 gauge from engine to body. The one shown looks to be the right size but the wire at the ring splice looks weak.
Good luck, Rob

i agree with fasttoys. your ground cables look marginal and the mention of going into gear changes the lights adds to that theory. your probably grounding through your linkages and shifting into gear changes your ground path. run a new ground cable from batt to engine then engine to body. also make sure your alt bolts are all tight and the connections clean.

[1project2many]

When alternator output is greater than electrical system requirements the regulator will switch on and off. This is normal. Quality regulators have a tight window between on and off voltage so the switch isn't visible. Inexpensive aftermarket alternators often use cheaply made voltage regulators and can vary 2-3 volts between kick in and kick out voltage. If the alternator is charging and the diode pattern is fine, it's probably the regulator working within it's normal parameters.

There are some things that you can check. If the regulator is sensing system voltage at the alternator rather than the battery then you need to ensure the power and ground cables are large enough and in good shape. High resistance will cause the voltage at the alternator to be higher than the rest of the system and the regulator won't get an accurate picture of the state of charge. You can also ensure the sense wire (if equipped) is routed to the battery. But it really sounds like a cheap regulator is at the heart of the issue imo.