View Full Version : Solutions for dimming lights at idle -72 RR

08-04-2000, 03:29 PM
Has anyone come up with a good solution for the feeble alternator/voltage regulators on late 60-early 70 Chrysler products? My lights dim significantly at stoplights. They virtually turn off in cadence with the turn signals. Don't even try to use the AC at idle unless you don't want to listen to the radio at the same time. I feel like that woman on Green Acres that could run the washing machine and the toaster at the same time. I have heard solutions like changing pulleys and such. But, I would really prefer getting either an alternator that will put out at idle, or a voltage regulator that will kick up at idle...even if they are not Chrysler products. Any ideas?

08-04-2000, 03:41 PM
I'm not an alternator expert, but I know that inexpensive, rebuilt alternators often do not have the diodes replaced, so one or more diodes might be burned out if you have one of these. The last time I had this problem, I went with a remanufactured alternator (at a higher price), and there was no problem. If you are running AC, I'd suggest buying a higher output alternator. My '73 Dodge truck with the trailer towing package always charges at idle, even when the load is heavy. I'm not sure of the output rating, but it's higher than the standard car alternator. I once bought a 400 from a police car and it had the alternator attached. I don't know what the rating was, but it was physically twice the size of the standard unit. A friend put it on his 4WD Dodge van equipped with a half-dozen huge driving lights. He said it had enough power to light a football field!

08-04-2000, 07:14 PM
In the old Chrysler alternaters, going to a higher (80 from 40 for instance) usually REDUCES the output at idle! I have very heavy fan, fuel pump,ignition etc. loads and could consistently kill a 210 reserve minute ambulance battery.

I swiched to a GM (Corvette or Camaro?) alternater, that puts out 80 amps at idle. It was easy to mount, one wire plus output and now everything can be running at idle and the battery stays full. Now I run a small Optima battery and never kill it.

I have also heard of some people working with Nippondenso alternaters with some success.

08-05-2000, 07:20 PM
Have you checked the whole charging system? The problem you describe sounds more like a bad connection in the charging system or a blown diode in the alternator. Pay close attention to the connections at the amp meter. One of my cars would do the same thing and come to find out the amp meter connections were corroded.

p.s. I have two old Mopars (late 60s and early 70s vintage) and neither one does what you describe. Have owned other early 70s Mopars with a host of electrical options and everyone put out a good charge when sitting at stop lights, etc.

08-05-2000, 09:47 PM
Yes, I have had the charging system checked several times....and let me explain why. I have put three alternators on this car since I restored it 5 years ago. They always stop charging while on a long trip...hence I lost an alternator on the Power Tour, the Yellowstone Cruise and Hot August Nights. Each time I have had the charging system checked to make sure the alternator is the problem...it always comes up as a bad diode pattern. But, prior to these long distance breakdowns, I always have this dimming problem with all three alternators. No problems if the engine is at about 1200 rpm...but at 750 rpm it will not keep up with any kind of load. I have heard of many others that have had this complaint and have solved it with pulleys or other contraptions. Seems the Mopar rags have an article on this about every other month. I am hoping for a slicker fix, and I am no longer concerned about keeping it a Mopar part. One other thought....I have always had to take whatever replacement alternator I could get since I have always been on the road doing this repair. Pep Boys and Autozone parts are usually all I can find handy....not the best.

Thanks! Merrill....72 Roadrunner 440

08-06-2000, 05:00 PM
Check for bad connection at the bulkhead connector. Try putting a jumper wire from alternator output to stud on starter relay, if situation improves problem is not the alternator but bulkhead connector or ammeter. This connection will make ammeter inaccurate and should not be of a permanent nature unless you install a fusible link.

08-07-2000, 04:18 PM
I would check your ground straps and Ground wires from the battery.

On my 72 Roadrunner I had removed the wire from the battery to ground on the header panel. After doing this I had no lights. Actually they were extremely dim. I replaced the wire with a 10 gauge wire and cleaned the areas for better ground. Worked like a charm.

Try to put in a extra or larger body ground wire on a clean section of metal and see if this is the problem.

The bulkhead connector is the second problem. I would be wary with this problem as I have had several bulkhead connectors get hot and short out forcing me to rewire and I had one fire in my car due to this. A small fire but still something to worry about.

Disconnect your battery and wiggle the wires in the bulkhead connector one at a time. If any of these feel soft then plan on replacing them. Check especially the larger wires these tend to be th major problems.


08-09-2000, 04:36 AM
You could also put a larger pulley on the alternator. That will make the alternator turn faster. It will still a couple of ponies though.

Ed - MoPower

'96 Dodge Ram 1500 SLT CC 360 4X4
'68 Charger 383-4

08-09-2000, 02:47 PM
Ed dont you mean a smaller pulley. A larger pulley will make the al;ternator turn slower. Unless you meant the crank pulley this would make the altenator turn faster.


08-10-2000, 01:28 AM
Christian - You are correct. Don't know what I was thinking, when I typed that.

Ed - MoPower

'96 Dodge Ram 1500 SLT CC 360 4X4
'68 Charger 383-4

Blaine Peterson
08-22-2000, 11:04 PM
Merrill, I'm no expert but I'd make sure that the connections at the ammeter (as has allready been suggested) are clean and tight! For what its worth I've had some real weird problems with my '69 Super Bee all because of a loose connection at the ammeter in the dash. At idle with the heater and lights on, the blinkers wouldn't work. With an engine swap and upgrade to electronic ignition and regulator, and different alternator the problem still surfaced from time to time. In fact things got worse! Every once in awhile my Mallory tach (electronic) would go berserk, the lights would dim, and the engine would ping like crazy at a very light load. One night it happened and I noticed the ammeter was straight up (no movement). I tapped the ammeter and things cleared up briefly. I then reached under the dash to check the ammeter connections and Holy Sh-t! It was hot as a fire cracker! Disconnected the battery, tightened the ammeter connection, reconnected the battery and gone was the problem that had me scratchin' my head for six years. Duh! Should have checked it first!

Just food for thought.

08-23-2000, 03:50 AM
Well, let me join in this saga! Similar problems to those listed, dimming lights, alt gauge all over the place, fluttering from charge to discharge, drive a guy crazy!
As a matter of fact today I put in another new alt just tonight, new battery cables, retightened the gauge nuts.......same thing, sigh. I'm gonna try one of the constant output voltage regs. I refuse to believe that these cars are supposed to dim at idle. (69 Charger). Years ago I had a 74 Charger SE and can't recall any type of electrical problem.
I've regrounded the block to the firewall, the battery to the block, all alt connections, new regulator, etc. I'm am really leary of driving her at night for fear that it will cut out and I won't be able to get it started again! Now I just read that someone had LOTS of troubles with the constant output regulator....damn. I have a 660cc amp battery, maybe its too small????? Thanks!!!!
Charger73....actually its 69 now, sold the 73!

08-23-2000, 03:57 AM
You may also want to clean the firewall connections really well. Alot of corrosion tends to form on those contacts, causing high resistance in the circuit.

My '69 Coronet is having similar problems. Maybe this coming winter I will tear throught the under hood harness.

I somepoint in time, somebody piggy backed an AC DELCO regulator with the correct regulator. It'll probably take me a good weekend to clean up that mess.

Ed - MoPower

'96 Dodge Ram 1500 SLT CC 360 4X4
'68 Charger 383-4
'69 Coronet 500 Convertible 440-4

08-23-2000, 10:15 PM
Regarding the dim light issue. I have a pot load of Mopars and they cover the years from 38 to 96. Not a one has this problem, anymore. Clean, tight connections in the entire charging system and a properly rebuilt (this means NOT a Slep Boyz, Autozoner, etc part) alternator to properly maintain system voltages.

My 65 Barracuda still runs it's "single field" alternator and a mechanical regulator, not an electronic version of it but a geniune relay clicker. Not dim lights. BUT I took apart the dash and cleaned, tinned tightened and repaired any problems, this included the ammeter. I also cleaned and soldered all the connections where a terminal was crimped to a wire.

My 87 Diplomat now runs the small ND 100A alternator but it has had the 70A and 100A Chrysler ones as well. All of them worked fine too. This car runs the constant voltage regulator and an Optima battery. I do NOT recommend the constant voltage regulator for a regular battery, it overcharges them and bulges the case out.

The Neon and Voyager run the ND alternator too and the factory, in the computer, regulator. The 38 has no electrical system, well it does in boxes but it'll be a Mopar charging system you can bet on that.

The person that claimed higher amperage CHRYSLER alternators put out less at idle is incorrect according to the factory service manuals I have. Both my 78 and 87 manuals state the 100A alternators are rated at a higher output at idle than the 60/70A versions.

Oh yeah, a new set of brushes usually helps too.


38 Plymouth P6
65 Plymouth Barracuda
87 Dodge Diplomat
89 Plymouth Turbo Voyager
96 Dodge Neon

"No quarter asked, none given" - Thunderstruck Racing