Lights go brighter when revs go up

[ThePointman]

I have just had my alternator rebuilt and reinstalled. I have noticed that the lights get brighter as the revs increase.

The voltage across the battery terminals is 13.7 which I think is ok. Is it?

My idle sits around 600-700 instead of what I would expect to be around 850 and it is rough. I have replaced the cap, rotor, plugs and just had the valves adjusted.

I am going to check the resistance of the plug wires. I would assume that if the wires are bleeding the idle would be rough and some cylinders may not be firing correctly if at all. I removed the plug wires from the number 5 and 6 cylinder respectively while the engine was running and noticed no change in how the engine ran while either wire was removed or replaced ...

I am thinking that I will just buy new wires, however if the alternator I had rebuilt is not functioning as it should the wires may be fine.

Thoughts?

[bell]

my carrera does that to, if the voltage isn't going higher than 13.7 then there should be no problem, an alternator will charge the car at idle but doesn't really produce significant power until it is spinning above 1200rpm give or take, which is why the lights get brighter when the alternator is spinning faster.

[porschenut]

Could this be due to a faulty voltage regulator?

[ThePointman]

Originally posted by porschenut
Could this be due to a faulty voltage regulator?

Voltage regulator was replaced when the alt was rebuilt.

[Glasgow 911SC]

Originally posted by porschenut
Could this be due to a faulty voltage regulator?

I had this problem & it was due to the V.R. I had other symptoms too however. The tach would occassionally jump 2-3k revs and taking a voltage reading at the battery showed a jump over the 13.7V periodically.

Swapping the V.R was fairly straight forward & an excuse to get my fan powdercoated

[SpeedracerIndy]

I have the same symptoms on my car. Rebuilt alternator with a new voltage regulator. it did the same thing before I rebuilt the alternator and replaced the VR. RPMs at idle when warm are about 750-850. My headlights are 80/100 watts if that matters. I don't think it's anything to worry about.

[donnieknoxville]

When my V.R. was in need of replacement, the lights would dim and brighten all be themselves with no driver input. I hated driving behind people at night because it was like I was flashing them constantly. The other symptom of the bad V.R. was the seatbelt light (the one that illuminates at start-up) would sometimes come on while driving, then come on, then off again. I've heard from other V.R. replacements of a similar symptom. In my case, when I removed the old V.R., the brushes fell apart in my hand (so it was time). I know you said the V.R. was replased with the Alt. rebuild but just some addtl. info from a 1987 Carrera Cab.

[ZOA NOM]

That is the specific function of a VR. It regulates the voltage so that your lights, radio, etc., don't experience varying supply voltage. Replace the VR.

[tctnd]

Suggest you have an auto electric shop look at it on a scope to insure all three phases are funcioning. Sometimes the alternator can lose 1 or 2 (of 6) diodes and will charge ok as it revs up but not be able to keep up with the load at low speed.
Usually this leads to the battery slowly going flat and leaving you stranded in Dismal Seepage Ohio on a Sunday night.