Lights go dim at low speeds.

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RPMagoo

RPMagoo

Just An Old Motorhead
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On My 65 Valiant - (318 - 12 volt - electronic ignition), The amp meter jumps around, and the head lights go dim at slow speeds. The lights get very dim at idle, for example while sitting at a red lite. - The battery is new - fan belt is tight - all other systems work properly. -- It's a 2 wire alternator - not sure what brand. -- What is the possible cause(s) ?
 
Your idle is not high enough to allow the alternator to make enough power to supply everything... Common on these old cars...

Try bumping up the idle a bit...

But not to where you have to fight the brakes to keep it stopped at a red light...
 
krazykuda said:
Your idle is not high enough to allow the alternator to make enough power to supply everything... Common on these old cars...
Try bumping up the idle a bit...
But not to where you have to fight the brakes to keep it stopped at a red light...
Click to expand...
-- This is not just at idle, the lights go dim at slow speeds on the highway. - I don't have a tach, but RPMs are quite a bit above idle.
 
Sounds like typical normal Mopar electrical operation if I ever heard it.
 
You could always swap in a higher axle ratio to get the rpm's up....
 
What parts of the system have you tested?
 
does the amp meter only jump around when the lights are on?
 
Did you do a charging system check? It starts out with a battery load test. Then goes on to alternator voltage output and if you have a inductive pick-up, you can do a alternator amperage output test. Then it finishes up with a starter draw test which isn't a issue here.

Well you have a 1965 and they have a mechanical regulator that basically controls the charging through a set of points. On and off if you will. The older Mopars usually flicker at idle due to the design and worse with a 50+ year old system. If you are just going to replace parts and hope for the best I would suggest a new regulator to start with. Most replacements now days are electronic and help eliminate the flickering lights at idle. Just one very important word of caution. Make sure the regulator case is grounded to the firewall very well. If not, the system will overcharge, boil your battery, burn lights out and could cause a electrical fire. Clean off paint where the regulator touches the firewall and use some star washers. Make sure the screws are tight.
 
Although I agree that the concept behind the headlight relays is sound, let's see what is going on before we suggest he start throwing parts at it. The headlight relays may brighten his lights with the more voltage, but maybe he has other problems. Magoo, have you tried checking charging system voltage at different RPMs? Have you had your Alternator checked (free at most parts places)? Have you checked your lights for a good ground? You said, "All other systems working properly." Does that mean you have already done the things I mentioned and are at a loss? It certainly sounds like a bad alternator or possibly regulator to me. Even at slower speeds, if you are driving down the road, your alternator should be putting out enough juice.-
 
harrisonm said:
Toolman Mike, you beat me to it. We must have been typing at the same time.
Click to expand...
Lol I see that. Start with the basics and never overlook the obvious. There are many in-depth diagnostic threads here on FABO. The op can just use the search feature to find them.
 
Here's a link and a diagram of what worked for me.
I installed a relay to insure that the voltage to the regulator was constant, no more flickering. Hope this helps.

Lights flicker and gauge jumps around???

Charging system relay modification.jpg
 
I tried everything thing to eliminate the flickering. I already had the Mad modifications and headlight relays installed. I went through 2 regulators (one from Advance and one from NAPA $35.00) before I ordered an adjustable regulator from eBay. This fixed the high voltage situation I was having but the lights were still flickering and my voltage gauge was jumping. After I installed the relay my lights no longer flicker and my gauge reads a steady 14 volts.
 
superchargeddrt said:
Oops sorry I didn't see that
Click to expand...
I didn't either at first. I had a overcharging problem on my 70 and fixed it with a Made in USA genuine Mopar regulator like you pictured above. No more made in China NAPA junk.
 
harrisonm said:
Have you had your Alternator checked (free at most parts places)? -
Click to expand...

Be careful taking it to a chain parts store to test it... Some of their machines "have difficulty" checking those alternators. The directions for how they hook them up is not very clear and when we had a brand new one tested, it failed every time... The guy was fumbling on how to hook up the additional wires to the alternator and where to hook them up to the tester.

After going through three alternators from that place and not getting a good one, I found a local rebuilder that rebuilt our old one... (good thing we didn't turn it in for core yet)... The rebuilder makes his own internals in-house and did a good job... He even verified it on his tester before giving it back to us... Not to mention that he recognized it as the old Chrysler "round back" alternator...

After installing the rebuilt alternator, we still had a charging problem, so we replaced the voltage regulator and it was fine...

Were the other store bought alternators really good or not??? Don't know, but I will keep going to my local rebuilder since he did a great job and knows how to hook it up to the tester and test it properly...

I don't like having to use my car as the test bench and replace the alternator 4 times because 3 of them were no good brand new or they didn't know how to test them properly....

I like to fix it right the first time and not have to waste time doing it over later...
 
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