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Chasing Dimming or Surging Lights

TX-ZACH

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Newbie
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Sep 27, 2021
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Chappell Hill Texas
I am assuming this is a grounding issue somewhere but not sure where else to look. I have checked as many connections that are visible that I can see. This started after coming back from a tub off paint job. Headlights and gauge lights have a dimming surge going in and out while engine is running. It seems to minimize once warmed up.

Looking clues to where to focus trouble shooting.
 

surfer-b

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Sep 7, 2006
Messages
2,972
Fresh Paint = bad GRNDS. More than likely its GRND. Chk voltage at battery with ign off and with Bronco running, I would guess its a combo of bad GRND for the voltage reg, the Alt, and the GRNDS for the lights and dash.
 

Steve83

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Jul 16, 2003
Messages
8,980
Loc.
Memphis, TN, USA, Earth, Milky Way
That's more likely an alternator or voltage regulator issue, but your signature doesn't contain enough detail to guess how yours is built. You should put ALL the truck's details (including the FG body) in there so we can review it all with each reply. You should also post pics of the battery terminals, alt., VR, body/frame/engine ground points, dash wiring...
 
OP
OP
TX-ZACH

TX-ZACH

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Newbie
Joined
Sep 27, 2021
Messages
287
Loc.
Chappell Hill Texas
This is a 77 Sport with original body. Fresh 351w but original or factory FOMO voltage reg and same alt and starter from old 302. Engine well was painted as well as repaint under carriage, replace minor areas with fab work. I will post up some pics and do a deep dive on voltage reg and ALT. From what I can tell grounds are snug but maybe inspect further on hitting raw metal on grounds. Maybe I will pull those off and hit with a grinder.
 

DirtDonk

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Nov 3, 2003
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47,345
That's what I do anymore. Relying on the threads of the fastener to do their job like they originally did is sketchy at best. Especially after new paint is added to the mix.
I don't take much, and then I spritz some paint on the area once the ground is re-fastened.

Check your main battery ground cable first. Is it just a single cable going to the engine block? Or does it have an additional wire going to the body?
Most people leave that last one out because they don't replace a ground cable with an exact match to the original. Ford had few enough grounding points as it was with Broncos, so adding some new ones in addition to reconditioning some originals is a good practice.

The alternator on a '77 had a small ground wire attached between the alternator body and one of the mounting screws of the voltage regulator. This was relatively important, but it's also possible that your original regulator is just not capable of working as designed anymore. Maybe it was before you pulled stuff apart, and simply decided to give up the ghost at that time.
I call them "coincidental failures" and they happen all the time on our older vehicles.

Along with the engine/body ground, an additional ground strap/wire between the back of the engine and the firewall never hurt anyone. It can only help with all this stuff.
Is the engine painted? If so then you might consider either scraping the paint off of the surface that the alternator touches, or add a secondary ground wire between the alternator and engine block. I don't know that it has to ground (maybe Steve83 can shed some light on alternator grounding), but that's a generally accepted assumption.
One other common area of "ground failure" is the radiator core support. It's welded to the rest of the body, but between old age, rust and new paint, it often loses contact with it's old friends the fender aprons.
Since the headlights and the turn signals/running lights ground to this panel, creating a jumper wire between the core support metal and the rest of the body (where the main body ground is, is not a bad spot) will guarantee happy camping in the headlight department.
Won't necessarily get rid of the pulsing, because that's more of a charging system issue directly. But it can only enhance the workings of the lights.
And speaking of enhanced workings... How do your wipers and dash lights and such work?

Back to the regulator, personally I would replace it with a high-quality new one (if there is such a thing anymore?) and save the original in a box of original parts in case you ever want to show it or sell it.

Paul
 

reamer

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Mar 20, 2008
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I now have 10 extra Body-to-Frame and Frame-to-battery grounds.....
 

Steve83

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Jul 16, 2003
Messages
8,980
Loc.
Memphis, TN, USA, Earth, Milky Way
If you suspect a lot of ground problem, stop using the ground system - add a return ("ground") wire through the whole truck so the whole circuit is complete through Copper wire - not reliant on rusty or painted steel (like most modern vehicles). Read the bottom half of this page:

(click this text)


Yes, it's extremely important for the alternator case to be properly connected to the B- terminal; either by wire (at LEAST as thick as the alt. output wire) or by grounding to the engine block, which then must be wired back to B-.

(click this text)


(click this text)


And it CAN be very dangerous to add ground wires... If they're not large enough (they NEVER need to be larger than the battery cables, which are 4ga), they can catch fire if there's a fault in the main (heavier) ground wire. So if you add one, make it substantial - but it would be better to simply abandon the grounds (other than small branches to reduce RFI) and add the large return wire through the whole vehicle.
 
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