I just installed a new battery to get my truck up and running this weekend. It was just a wee bit smaller than the one that was in it previously. So I was driving it down the road this evening trying it out and I noticed that the headlights are pulsing-going dim then normal then dim again, etc. Could this be a failing alternator or is the battery possibly too small? I'm far from a mechanic but I am trying to learn how this stuff works!

Thanks,
Shane

 

Could be:
Dimmer switch shorting out from corrosion

Headlight switch is weakening as circuit breaker is going on and off.

Ground connection of voltage regulator to fender..clean and secure with di-electric grease

 

I had a problem with a 78 I got rid of (kick, kick, kick). Driving along @ nite when headlights would just go out and then come back on, not fun on back country roads. But I do believe it was a bad headlight switch.

 

Sounds like either your alternator or voltage regulator.. as suggested above, make sure all connections are clean. I REALLY doubt its your headlight switch..

Take it and have the alt tested.. either bench tested or on the vehicle.

 

Original 1973/79 Ford truck battery sizes: R-24-F; R-27-F; R-27-FA

 

does it do it with the high beams on? if i remember correctly the lights flash on and off. then get worse. probably the headlight switch. if you think its a battery or charging problem go to autozone, advance and i think oreilly will check the battery and alternator for you.

 

It doesnt seem to do it on high beams as badly. I just put a new battery on so its not that (unless I bought a battery thats too small for the engine). I pulled the alternator this evening so I'll get it tested tomorrow. Maybe that'll be it, cheap fix if it is.

Thanks!


Shane


EDIT: Forgot to mention, sometimes the cluster lights work, sometimes not. Could this be related?

 

Had a similar problem many years ago on mine. The lights would pulse at idle.
Pulled my hair out trying to fix it and finally discovered that I had forgot to hook up the ground strap that goes from the rear of the intake to the firewall after swapping engines.

 

Before anything...clean and secure all connections including grounds.

Then and only then...see what happens

Both ends of both battery cables

Voltage regulator mounting and the tabs on the connector.

Any Ground straps

Alternator connections

 

Is this a braided flat cable? There is one loose back near the heater blower, I didnt know what it was.


Shane

 

Yes, it is. Tighten that.

 

Turn the lights on and vigoursly shake the dimmer switch. If that causes problems before you buy a switch, check and clean all connections for corrosion and make certain they are tight. When I worked in auto parts in the late 60's and 70's, Ford dimmer switches were a hot selling item. Most garages and gas stations doing mechanical work usually had a few Ford dimmer switches on the shelf because they sold so often. If your dimmer switch is bad, get in a habit of gently pressing it straight down. A common cause of failure is caused from pressing it from an angle and eventually bending it slightly. Many drivers, myself included have a bad habit of pressing hard, or slapping it with our foot by hitting it from an angle leading to the switch's demise.

 

and just before you re-install it ....coat the back of it with di-electric grease so corrosion won't take place