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Dim lights everywhere

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Vic Roma

Dim lights everywhere

I see a lot of owners talk about dim headlights, and dash lights etc., and known fixes include headlight relays, LEDs especially in the dash, 3G alternator, adding extra grounds, etc.

However, all my lights are dim; headlights, interior lights, tail lights. My lenses are clean and clear (PO installed TYC tail lights) and everything works, but all lights are just not bright like I believe they should be. Someone on here (I think it is Gary) wrote although a 3G upgrade is good if you need it, on a factory rig with little to mods, 3G is unecessary. My truck is unmolested best I can tell, so I’d like to know why the lights are dim and what can I do about it.

I am thinking this is nothing more than age-related deterioration within every component of the electrical system. Am I correct?

If I am / it is, what are the possible solutions?

I am not at the truck to test alternator output or battery levels, but maybe an alternator replacement is in order. A rewire is not, as there are no replacement harnesses available.

Does anyone have experience with this conundrum?

1984 Bronco 351 Holley Sniper EFI, 3 Speed Ford Auto.
1986 Bronco 302 EFI, AOD, Eddie Bauer, with 3G alternator.

Gary Lewis

Re: Dim lights everywhere

Administrator

Is this when going down the highway or at idle? I ask because one problem with the 1G & 2G alternators is poor output at low RPM. In fact, as Jim said recently, a good 3G will put out about as much at idle as a 1G will at full tilt.

The difference is that with low output then your accessories are probably seeing 12.8V as opposed to 14.4v. And that makes a very big difference in the light output of incandescent bulbs. Actually, the calculation is voltage to the 3.5 power, and the little calculator below lets you play with that. But, as it pops up you can see that you only get 2/3 of rated output at 12.8 volts since most bulbs are actually rated at more like 14.4 volts. But that isn't true of LED's. While they drop of in light output it isn't as dramatic.

So, a 3G alternator isn't necessary. But it sure helps.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

Gary Lewis

Re: Dim lights everywhere

Administrator

Oh, I also should have said that a headlight relay harness is highly recommended. Back in the Bullnose era most manufacturers used itty bitty wiring and ran it into the cab to the headlight switch and then all the way back to the headlights. And by the time the juice got there the voltage was decreased well below battery voltage because of all of the resistance in the circuit.

In addition, the resistance creates heat which degrades wiring, connectors, and switches so the resistance thereof increases. Which creates even more heat, which...... And many Bullnose trucks have had a headlight switch or the associated wiring fail due to that.

But the headlight relay fixes that. It only puts a very small current through the old, skinny wiring and the switch, and leaves the heavy lifting to much larger new wiring and relays. So more voltage gets to the headlights.

Gary, AKA "Gary fellow": Profile

ArdWrknTrk

Re: Dim lights everywhere

Administrator

In reply to this post by Gary Lewis

Actually I said the 2G (firestarter) like mine was...
They only came in 65A, which should be plenty.
Whereas the 1G had different 'flavors' up to 100A Iirc.

Vic, if you have a 1G, I'd be looking at what the external regulator is putting out for voltage, and if you have an ammeter, how much resistance is in the shunt wire.

If system voltage is below 14.3 at high idle or you're seeing under 14 at the far end of the shunt running, I'd consider replacing either of those items.
Also, do a full field test -for a moment!- to rule out the alternator being weak.

Just my 2c

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Gary Lewis

Re: Dim lights everywhere

Administrator

Ok, 2G. Which is what Vic may have since his is an '86 and that's when they started using them.

As for the 1G going to 100 amps, yes but what I've been able to glean that was with the ambulance package and that didn't come in the F-Series, only the E-Series. It looks like the F-Series got either the 40 amp or the 60 amp.

Gary, AKA "Gary fellow": Profile

ArdWrknTrk

Re: Dim lights everywhere

Administrator

I think the high amp ambulance package had a Leece-Neville, and later Mitsubishi, alternator.

At any rate it's worth checking the system voltage, and harness resistance.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Gary Lewis

Re: Dim lights everywhere

Administrator

Yes, checking the voltage and resistance is a good idea. But, the resistance is best determined by checking voltages with full load on. Most modern meters aren't good at checking very low ohms, but are good at low voltages. So checking from the battery's positive post to the headlights, for instance, will show the voltage drop in that circuit - and it will be highest at higher RPM since system voltage, and therefore current, will increase with RPM.

Gary, AKA "Gary fellow": Profile

ArdWrknTrk

Re: Dim lights everywhere

Administrator

Which is why I said check voltage at high idle first.
Checking for voltage drop to the headlights is something I didn't think of, but a good test.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Gary Lewis

Re: Dim lights everywhere

Administrator

On the RPM issue..... The page here (Documentation/Electrical/Alternators) has info on the alternators and loads and shows that headlights on high beam pull 11 amps, but the other lights will pull a couple of amps, so that's about 13 amps total. And A/C pulls 26 amps. So it would be easy to have a load of about 40 amps.

But the alternators don't put out that much current until at least 800 RPM for the 351W w/a 60 amp unit and more like 1200 RPM for the 40 amp unit. So it'll have to be on a true fast idle to bring the voltage up with much load on.

Gary, AKA "Gary fellow": Profile

ArdWrknTrk

Re: Dim lights everywhere

Administrator

Engine rpm, or alternator rpm????

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Gary Lewis

Re: Dim lights everywhere

Administrator

I was talking about engine RPM, although there are charts in there for alternator RPM. Here are the charts I was using:

Gary, AKA "Gary fellow": Profile

ArdWrknTrk

Re: Dim lights everywhere

Administrator

Interesting what a pulley swap can do. 👀

And I wasn't aware the little Ranger was available with a 2.3 TD in '85

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Gary Lewis

Re: Dim lights everywhere

Administrator

Yes, a pulley swap can make quite the difference - if you don't throw the windings off from too much speed.

As for the 2.3 TD, I didn't see that in the list until you pointed it out. Interesting. I've never seen one.

Gary, AKA "Gary fellow": Profile

Danny G

Re: Dim lights everywhere

It was only offered for two years 85/86 before that was the 2.2l Perkins.

Low power along the same lines as the VW Rabbit pick up 1.6l/1.9l diesel, got in the 40mpg range.

1986 F-150|Standard Cab|4x2|300Six|C6Transmission w/3.08 rear|Name:TBD
2021 Ranger XLT Super Crew