Hi guys, 1966 352. Put a new altenator in. started right up. Alt light on dash came on, (wasn't on with old alt). But when I rev the engine light goes out. engine comes back to idle and alt light comes back on? rev engine, out, back to idle, on.. ??
Other then that, all systems are good. New alt fixed problem with lights dimming and such.
I do know wires are old and truck came from AZ, so they are brittle.
Can't find anything on the web on this.

Any help would be greatly appreciated!!

Joe

 

Put a meter across the battery posts with the engine idling. Should read 13.5 volts. Turn engine off. Measure battery voltage should be 12v. Rotten wires and flaky grounds can cause problems. Sounds like the Alt is putting out at higher rpm and not at idle. Weak battery may not be accepting charge like it should. You could try cleaning the bulk head connections and the regulator connections and lube them with plenty of bulb grease.

 

William, will give it all a shot and report back. Thanks for help.
I was thinking I should replace regulator also as it is original.

 

Thought I should post the update I did with new alt to see if this is causeing problem. I updated to a 65 amp froma 50. Truck is a 66 camper special. regulator is original. should I get a new regulator also because alt is now a 65 amp?

thanks!!

 

Getting a little over 12 V while at idle. 12V off. Battery is new. same thing. on while at idle, off when at higher rpms. Should i replace the regulator?

thanks!

 

Newer regulators are solid state and smaller than the original should plug in the same. I switched to a 12SI delco one wire years ago and tossed the Ford alternator, regulator and rotten wiring. Only thing from the original was the green alt wire. Wrote a tech article that is still here in the tech section. Better deal now is the Ford internally regulated 100 amp system. Not sure where you are on this but if the issue is rotten wiring, I'd switch the old system out for the Ford 3g deal available on ebay. IMHO!

 

Since you replaced the alternator, if if your regulator is original, you should go ahead and replace it. Look how long it has worked!

Also, how slow does your truck idle? The alternator can only make so much voltage at a slow idle.

If nobody has butchered the wiring in your truck, and the connections are all snug and tight, I see no reason for the wiring in your truck to be a suspect here.

 

Just put new carb on truck, does idle good. Ya, everything seems to work good, just the alt like coming on now at idle speed. I shou8ld of upgraded to the new system. But didn't do my home work before I started. Its my 2nd restore, last one was when i was 17 yeas old. Am a grandparent now. LOL
I will pick up a new reg and see what happens.

THanks for all your help guys.
this is the best board for info!

 

I love an old truck.

Your alternator will probably run more efficiently with a modern regulator, too.

If you knew me, you'd know that I'm the one that likes to run parts until they absolutely die... but in this case, a mechanical regulator has points and relays that open and close and are probably fairly toasted by now.

When you take it off the truck, look inside. It's a nice little piece of workmanship.

Be sure to clean corrosion off the truck body where the regulator bolts down. Regulator grounds to the frame.

 

Thanks again! will do. Am also going to check all the wiring and check for good ground. I know some of the wire casing cracked what I changed the alt out. But I taped it all up and it isn't touching anything. It didn't seem to be putting out 13.5 Volts thought when I check it at idle. It was just a little over 12. Like 12.5
Ya its a 1966 camper special with 82 original on it. from AZ. Body is almost perfect. just needs to be sanded and painted. But it does have that AZ "burnt" on it. wires are all brittle. Will do a total wire replacement next winter.

Appreciate your help!

Joe

 

Just a question, where did you get your alternator ? Most are remanned out of this country and not all are created equally. If you bought it at a major autoparts store take it to them and have them warranty the alt. until you get one that puts13.5 +/- out at idle.

 

I got it at Oreilys. It does have a life warrenty. Good point. it is a reman. If the new reg does not fix it. I will be bringing it back. But then I will probably update to modern. Like listed above.

thanks for the advise!

 

I must agree with bunchoftrucks. I go through this all the time with motorcycle alts. I work on them all the time. Not every single alt you buy will put out X amount at X rpm, even if it came off the same rack at the parts store. They should but not always the case. It all depends on how accurate the winding is inside the alt. IE - size of wire and # of winding. It just may be that the new alt you installed will not put out X amount until the rpms are up to X. While your meter is on the battery, turn up the idle a little at a time to see just when it starts to put out 13.5+ volts. If you don't have a tach - see if someone will loan you one. It just may be the higher output alt you installed will not produce what you need at idle. It also depends on acc you may have on at idle. Also as stated above, it could also be you regulator that is not reading the new alt. Your battery is really only there to start the motor. Try this, while you have your meter hooked up to the battery, turn on the lights and see if the alt kicks out more voltage. The more stuff you turn on will make the alt put out. If your regulator is not doing its thing, maybe thats your problem. If your wiring is bad, it may not show up until you put a big loan on it, which will heat the wiring up - that is if the wiring you have can't handle the load due to size or bad connection.
I would most definitely install a new Reg, if the problem is still there, take it down and have them check out the alt output (and at what rpm) on there machine. Most places will have a way to test this.
A little note: I have alt rewired all the time for applications that require a large load. Only problem with this is, on some of the alts, it takes a little higher rpm to start the output unless you turn on a little more load - which at that point, the reg sees this and tell the alt to putout.

 

I know this may sound (STUPID) but is your alt' belt ''Tight'' ? I had the same prob and turned out the belt was slipping a little at idle, but not enough to make any noise?
rev it to 1500 rpms and fine, back down to 650rpm and light came on!
just a thought?

 

Huckduceman! Great answer. Sometimes we get so caught up in exotic analysis we miss the most obvious and basic troubleshooting techniques. I once changed out a thermostat due to an overheating situation when the real problem was a low coolant level.