I get the old "lights dim at low idle" voltage issue. Just to make sure I didn't miss anything on the grounds I whipped out my FSM's and guess what.... they focus on the positive, not the ground. I never knew that until I looked tonight. (that's dumb)

I did my searches and found several diagrams on aftermarket grounding. I didn't see anything too helpful about the factory grounds, but it's pretty idiot proof...... find the ground and sand it. So I did. I sanded the body ground at the top of the firewall that goes to the manifold. I could not find any way in hell to get to the other end of it. I sanded the ground at the oil/ac (main ground) and I sanded my battery terminals and clamps including the input wires.

I sanded it all. Still does it.

I don't have any dimming issues with the dash per say, just the headlights and door entry lights are noticeable when the car is at idle and in gear. It seems that the alternator is slowing down too far and is causing the voltage threshold to drop under the regulator.

The alternator is a new one and it's cranking the juice out all the time above 14v. Just that time that I am in gear and stopped that produces a low idle and thereby drops the voltage.

I don't think it is a ground this time. I don't think the regulator is bad either. It might not be doing exactly what it is supposed to be doing, but it works.

Can I change the regulator to a different one that will hold the voltage up at a lower idle? I'm at about 650-ish rpm's out of gear and maybe 500-ish in gear.

 

i would think the only person who could fiugre this out is you... heh, hope you figure it out =)

 

I have done the numbers and the only thing I can figure is the voltage regulator is not holding at the lower RPM like it should. What I do not know is if it is supposed to hold at 500 RPM or drop. All drop a little, but this is at least 1.5 volts.

The problem is I don't know if it is a problem. LOL. I guess I need to know the voltage of another SC400 when it is in gear, headlights on, brake applied, AC OFF. (and maybe throw in a blinker for good measure for a second test.)

Putting a bigger alt on it will only increase the problem by increasing the load and dropping the idle even more since the bigger alt will be harder to spin. I wonder what my regulator options are..........

 

You know how they say "we'll go put it on the machine"? I have the machine. Everything looks good, but I can't get too in detail since this is not an OBDII car. I can read everything an ODBI car can tell you.

My lowest RPM I could get was 675. In gear, brakes on, headlights on. 800 was the normal idle in park with everything off.

 

no youd want to put a smaller pully to spin the alt faster !

 

I have a similar issue as well on my 93 sc300 with 97 front bumper fogs. I had the good ol' electrical ghosts where the cluster/radio would dim when I signal or brake. I installed a new alternator and it still did the same. Cleaned the ground by the battery and still did the same. I replaced the negative battery cable a few weeks ago and the issue has not showed up since. So one night I put on my emergency lights and noticed that my headlights dim noticeably everytime they flashed. Interior lights do not dim at all just the headlights. Also my passenger side fog light does not light up even though the bulb is new. I may try to replace all the front signal and taillight bulbs with oem ones to see if it does anything.

 

I dunno if I can tighten the belt enough to compensate, and I might be worried about excessive wear on the alt.......... but you may be onto something. I just have the theory that it should not be dropping voltage in stock form anyway.

 

My ground cable looked really good, but I was thinking it might be tarnished maybe more towards the center of the cable even though the ends looked good. Given enough time, the cable is not oxygen free and will tarnish all the way through. I have plenty of 4gauge and 8 gauge from when I used to own car audio stores. (small pieces in old boxes) I might grab a few of my old stinger gold terminals and give the car one heck of a fancy ground

 

naa not going to premature wear just run a smaller belt yes your correct not to drop voltage anyways but it does

 

We'll do this for the heck of it. No harm can come from good fresh wires. The jacket is softer than OEM, but even if it gets soft under high heat and grounds ........ ok so? it doesn't pose any issues, and I doubt it'll have problems since it is designed to run under the hood.

 

This outta get it done.

 

Cool man can't wait to see the results and if it cures the dim headlight issue.

 

Nope. Didn't change anything. It's definitely a voltage issue with the regulator not holding at 675 RPM's.

When I first started the car and the high idle came was on the lowest I could get the rpm to drop was 775 and it held through everything except the rear reverse lights (which with the brake on, the headlights on, and in gear will dim nearly anything a tad).

Once the high idle cam kicked off and the RPM dropped to 675 the symptom came back. (almost thought I had it fixed for a split second).

Absolutely the regulator not holding at 675. No doubt.

Wonder what diameter pulley would increase the rpm drive to the regulator by about 150 rpm.

 

got a pic of it ? the alt pully

 

good thing I have a completely stripped parts car in perfectly organized boxes stored away