The lights on my 70 SS (interior and exterior) get dim to almost nothing when I'm idling, but get brighter as I speed up and the alternator spins faster. The alternator belt tension is fine. I have the original alternator and voltage regulator on the car. Do I need to replace both or jsut the regulator? Also, is there a way to check the voltage regulator to ensure it is operating fine?

Ron
1970 SS 396

Also, is there a way to check the voltage regulator to ensure it is operating fine?

Ron
1970 SS 396

Yes, with a voltmeter. Check voltage, at battery, with car running. Normal charging is 13.8-14.5 volts or so. Your voltage at idle is probably low 12.5 or less, causing the dimming. A low battery only make the condition worse. If the voltage is to high (15+ volts) at faster engine speeds the points in the voltage regulator may be stuck closed.

Personally, unless the car is 100% original, and you have to replace anything, I would convert to a internally regulated alternator.

RON,what your experiencing is very common with the older ext reg ele systms esp with auto trans where idle is low like 600-700rpm in gear.

Those ext reg alts dont put out much at lower rpms and its common to see light dim at low rpm idle in gear Thats esp true if the battery is partially discharged to begin with due to lack of use/lack of charge for battery if car site for days and or wks at a time with non use/no charging.

But if the car is running ok and starting ok (esp when hot)with no issus at all its nothoing to worry about al all.

GM sold litterally millons of cars with ext reg alts that did just what you describe for the lives of the cars and they went millions of miles collectively doing just what you describe.

Can you upgrade to something newer/better ,sure but if your not running a wild setup that draws a lot of amps a properly setup operating stock ext reg gm elec system with a known good 61 amp alt ,good volt reg,and all connections/grnd in charging system clean & tight etc will work fine in 9 of 10 cases.

Add elec cooling fans,elec fuel & or water pump ,elec ign like msd box,hot 200 watt stereo etc and thats a totally different story. In that case you will have problems with stock system for sure needing to upgrade to a newer 100amp+ int reg alt in that case.

There is a time and place where an upgrade to a hotter intern reg alt is required but not for a stock motor or mild motor in a muscle car with little to no elec add ons that draw a lot of amps. Thats requires that the stock elec system is working properly with the stock system setup right with good quality battery thats been load tested to ensure its ok/fully charged if it's not new/fresh .

Chlk the voltage as Greg suggested and if it chks out ok and your not having any starting issues dont worry about it.

But ify ou are having starting/charging issues but there are no additonal add ons you just need to diagnose what the problem is and fix it weahte r it be a tired alt and or battery and you should be ok.

I have run the stock ext reg chagring system on bbc for over 30 yrs with no starting/charing issues ever.

I have a friend that has 4 gm muslce cars he shows that i maintan for him for many yrs and not 1 of those all 4 cars with ext reg systems have had any starting or battery charging issues and he atteneds plenty of shows that require night driving too.

They are all cars in show cond with good restored alts all putting out what they should be along with all else right like it should be too thats why he has no issues with the stock system everyone thnks must be upgraded. and he doesnt use battery manitainers so his car batteries are often down as far as state fo charge goes when he starts out for a cruise/show and still exp no issues . with this guy i do work for you can bet he would be complaining to me about it because he drives me nuts over nothing and having starting /dead battery issues would be a major deal to this guy i would have to address.

Point is it's more of an issue with people messing up the lec systems and or taking appart and or incorrectly rebuilding these cars over the past 30-40 yrs that casues most of the battery/charging issues from what i have found over the 37yrs working on them. It's not just that its an ext req alt system that cant work right by design which just isnt the case when they are setup right to factory spec with a 61 amp alt.

But i dont rec 37-42 amp alts esp if you do a lot of night driving that hits a fair amount of traffic because they are marginal. In those cases i suggest upgrading to a 61 amp alt that does a little better job in traffic and also recharges the battery considerably faster when you get out of traffic back up to speed with alt/engine rpms back up to where the alt puts out more umph.

Jst my 2 cents on that one.

Scott

Check the voltage at the battery. If it's low, you need to fully charge it; and verify the alternator and charging system wiring.

Check the voltage IN THE PASSENGER COMPARTMENT, perhaps at the fuse block or the cigarette lighter.

If you have more than about half-a-volt difference between battery voltage and interior voltage, your wiring to the passenger compartment has problems.

This is common as dirt; the battery is charged properly by the alternator but the power supply into the passenger compartment is compromised; the interior is perhaps 2 or more volts lower than it should be; and things just get worse when you turn on the lights.

The only fix is to repair or upgrade the power supply to the interior. (Although running the headlights from relays under the hood will improve things--both at the headlights and in the passenger compartment.)

But by all means start with the battery and charging system first.

Thanks fellas, this is all great advice. I'll definitely check the battery. I have it charging right now. Living in New England and parking the car for 4 to 5 months results in a dead battery, so I take it out of the car for the winter and charge it when it starts to get warm or when I start working on the car and need the electrical.

I think I'm going to replace the voltage regulator regardless of the battery condition, just to be sure and have a good starting point. I bought the car restored and it runs, starts great. The only thing that has given me trouble is the electrical lighting. I think I've removed a mile of useless wiring from the car. All of which plagued me with bad grounds and shorts that kept turning off the lights (interior and exterior). Now that everything works, I am just fine tuning it for more night time driving.

One more thing and I think the voltage regulator will fix this, but the two lights for the auto console that light up the gear selector only get about 8.5 volts, while the courtesy lights get 12 volts. I figured the 8.5 volts would at least show a dim light on the gear selector, but I get nothing. Keep in mind I measured this without the car running and just drawing from the battery. Still I thought it should read more than 8.5. Any more help would be great.

Ron

Ron,get the Wells VR715 updated/electronic volt reg replacmenet for the older design ac delco D635 mechanical v-reg.

The VR715 shoule be avail at autozone/advanced auto/etc & is a much better replacment unit then the older design mechnical v-reg.

BTW,that battery has seen a lot of sit time with no charge activity which causes plate sulfation and premature degradation of battery power/amps.

So with that said after its charged take it to the auto parts store or local shop to have it loaded tested,you want to have at least 500CCA(not CA) orgood dependable hot starts.

Even if it passes a load test i would still top off the charge again after its loaded tested becasue doing a load test can birng the battery's charge back down a bit esp if the battery is a little tired/old as yours seems to be from what you say.

Scott