Dimming headlights on acceleration

[jgf100]

I replaced my '70 harness a couple years ago and I just noticed an issue with dimming headlights. I noticed headlights will get brighter after a second or two after I take foot off accelerator. Headlights will dimm after using accelerator. They do not dimm to the point that they are unuseable nor do they blink. Battery is not being drained when not in use, but Amp gauge is running higher. Any suggestion on how to track down cause.

[cep62]

double check and add grounds.
Run a good ground from the battery to the rad support and to the inner fender , preferably to the solenoid hold down screw

[MadMike]

I replaced my '70 harness a couple years ago and I just noticed an issue with dimming headlights.

Why was the harness replaced?
Was anything added to the truck that is non-stock? Such as an electric fuel pump?
Is there anything non-stock(factory) on the truck?
Have you added anything to the truck that may have been a factory option(stock) that was not originally added to the truck(cab lights/trailer harness/upgraded radio)?

I noticed headlights will get brighter after a second or two after I take foot off accelerator. Headlights will dimm after using accelerator. They do not dimm to the point that they are unuseable nor do they blink.

If the lights are dimming upon acceleration there is either a loose connection that is moving and causing a bad connection with a loss of power from the alternator to the battery, or there is a high power drain that occurs from a loose connection(grounding out), or there is a high power drain from a component that increases with engine demand e.g. electric fuel pump.

Battery is not being drained when not in use, but Amp gauge is running higher. Any suggestion on how to track down cause.

How do you mean the Amg gauge is running higher?
Is is going from middle to 'C' after acceleration or is it visibly going from 'D' on acceleration and then swings to 'C' upon deceleration?

Verify battery is fully charged and holding a charge. Fully charged battery will be 12.6Volts. 12.4 is acceptable but not ideal. Anything below this is a drained or dying battery. 11.99V is a dead battery. Battery may need to be load tested, might show full voltage no load, but under load it may drop.
Verify system voltage with engine running. Nominal should be 13.5V running no accessories. Voltage should not drop below 13V idling with accessories on.
Verify all connections are clean and tight.
Verify all ground and bonding connections are installed, clean and tight.
Verify all components are mounted correctly and not loose, battery bolted down to the battery tray, battery tray bolted to body, engine mounts not broken... etc etc.
Inspect any components that may be loose or possibly shift during acceleration.
Alternator to Voltage Regulator harness is secure and does not create a make/break connection when shifted around.
Verify Alt to V.R. harness connections are clean and tight. Use a conductive grease(not dielectric!) to promote a good connection. It may be hard to see but the connections inside the V.R. connection can be released using a pick tool, slide the connector out and verify the connector is not corroded/loose, clean and replace connector if need be, .250" female spade connector works fine, just remove insulator collar to fit inside factory connector.
Verify Alt to V.R. ground wire is intact, clean and tight.
Verify V.R. male connections are clean. These can become corroded and hard to see when V.R. is bolted to the inner fender.
Verify V.R. and Starter Solenoid are both properly bolted down. Factory sheet-metal screws are only used for fast production, not for best connectivity.
Replace those sheet-metal screws with good 1/4-28" bolts, washers, and nylock nuts.
Clean the mounting feet of the V.R. and sheetmetal to bare, add some conductive compound(Ox-Guard, Noalox), NOT DIELECTRIC GREASE!
Bolt down the components snugly for a solid ground.
Find any other body grounds and verify they too are clean, metal to metal contact, add conductive grease, and tighten connections.