on my 68 GT500KR, when the engine is running above 1000 rpm, the interior lights cycle between bright and dim. Below 1000 rpm, they are fine. Is this the voltage regulator? It is a fresh restoration and I replaced both the alternator (from AMK) and the regulator. Thanks for any thoughts.
I think this may be the instrument panel regulator...
Assuming you are talking about the instrument panel lights -
this sounds like it might be the constant voltage regulator that goes behind the instrument panel. Are your gauges also fluctuating?
If you are having the problem with the dome light - you may have a squirrely voltage regulator in the engine compartment.
You may want to also check the ground on the instrument panel.
THe CVR will affect the gauges. It sounds like when the alt gets up to speed and starts pushing a charge to the battery-meaning the current flow increases to something more than a small trickle ( at idle) that a gound connection is breaking down somewhere. WHat is the voltage output from the alt above 1k rpm? SHould be around 14v or so. Curious to know if that measurement is a lot higher than 15v...
THere is a ground wire that should be attached behind the inst cluster, if that is off, it might cause a problem. If the gauges work then it's probably attached...
If its ALL the lights, including tail lights, headlights, parking lights, etc, then I would also lean toward the voltage regulater, and/or the alt. I've (rarely) seen a failed regulater take out the alt and vs versa and you chase the two parts around untill you replace both at the same time...have you have a parts stor spin the alt to check it out yet? New does not mean good...
Will be intersting to see what fixes this.
Sounds like you have a decent Alternator - you said you replaced the voltage regulator - was it a decent brand? I have had problems with some of the Duralast cheaper replacement electrical stuff. I would think the AMK alternator would be OK, but some of the concours-correct stuff (like coils) are junk, too.
If you have good quality parts on the car - have you also replaced the solenoid? I know this sounds weird, but I had one of the cheap ($5) Duralast solenoids on my Mustang and it only had 7 - 8 volts coming out of the back side. Went to NAPA and paid $15 for a solenoid that solved my problems.
The quality of this imported newer repro stuff is terrible - I had two $15 ignition switches literally break in half in a year - I bought an original for $35 and have not had a problem since.
If you are working on a GT500KR, you should get the good stuff.