933005spd

Ok, so this is funky - I thought my electronics problems were gone with my LHS years ago....

My 93 300 occasionally losses power very briefly to the radio and lights, this happens when the brakes are applied or the turn signals are activated. But not always and when it happens, it does every time the signals or brakes are used for a few times then stops happening.

The guy I bought it from told me he thought it had to do with the built in phone, but I properly removed it last week. Also, the rear view remote adjuster **** does not work, could this be associated???

LEXUSDOC

The problem you are having is high resistance in your
negitive ground cable. See it all the time and have
replaced hundreds. You have 2 options. you could by the
whole harness for $250.00 or use the ground cable off
the gs300 that goes for about $65.00 list price. The gs
cable fits great! You have to separate the old ground
cable from the harness. Real easy.. Good luck

Doc

LEXUSDOC

By the way the part #82123-30200

stoplight

933005spd:
I asked this question at Ladman a while back because my car is doing what you describe when the brakes or turn signals are first activated. I am able to notice the voltage drops (power loss) in the brightness of the headlights and dash lights, especially at night. The weird thing is that my voltage drops only last about a half of a second, like the voltage regulator is slow to react, however, I know this is not the case.

LexusDoc: Which ground cable are you referring to? Battery to chassis or other?

My original question to Ladman:
What should the voltage be on a 92 SC400. Mine shows 14.2v on a digital multimeter across the battery when it is cold regardless of electrical load. As the car warms up, it slowly drops to 13.7v when hot. When a load (everything electrical on) is applied the alternator maintains the same 13.7v, however as each load is applied the voltage drops a half a volt or so momentarily and then pops right back up. It acts as if the regulator is slow to react to the electrical demand. No big deal I guess but when the turn signals are on I can see the dash lights dim slightly with each turn signal flash. The alternator does not appear to be weak as it maintains voltage regardless of load.

gadgetSC

LexusDoc, sounds right......I had the same problem awhile back. Turned out to be a bad connection on the negative battery cable. Before you replace the cable...you might want to take a little time just to check your connections. Make sure they are clean and tight
Good Luck


gadgetSC

933005spd

The loss of power seems to only happen at night, and I have to drive for a few miles first. Yep, the lights dim at first, then as I brake again or activate the turn signal more and more times it eventually clips everything off and then the cycle starts again. And yes, it is only for a split second then everything is back on.

I will check connections first, then try to replace the cable.

stoplight

LEXUSDOC & gadgetSC, you were correct about the negative cable. The first owner of my car had a quick disconnect installed on the negative cable to save the battery as it was garaged for extended periods. I tightened and cleaned the connections on the disconnect and seem to have fixed the problem.
I don't understand why the power loss was only momentary and why it didn't ever happen when the engine was cold. I know the alternators are controlled by a microprocessor voltage regulator and are compensated for temperature. When the engine and battery are cold the voltage output is supposed to be higher to recharge the battery and then taper off so as to not overheat and damage the battery.
I did more reading on alternators and charging systems, and spent more time running around the electrical system with a multi-meter than I care to admit, and it turns out to be so simple. Thanks for the help!

gadgetSC

Glad you found your problem. Was that quick disconnect one of those green *****??? Thats exactly where I had my problem...and it was exactly like you described!

gadgetSC

stoplight

You guessed it again. The dreaded green ****!
By the way, the reason batteries tend to drain over time when parked is due to the keyless entry reciever. It is alot better to turn off the reciever (by the switch near the trunk and gas release) than to put on one of these green knobbed, brain teasing, battery isolating wonders. IMHO

Stoplight

LEXUSDOC

For some reason and I will never know. The SC series has always been very sensitive on the ground side. A good way to always test that ground cable is by doing a voltage drop test. Any more than .2 volts a goast will come and visit. On...... say a ls400 it could have the same high resistance in the ground cable and not even have a symptom. Gotta love them coupes.

Doc

933005spd

Hey there doc>>> What about running an additional ground strap to the chassis? Would that help? How about upgrading to an Optima Yellow or Red top?

933005spd

Well, I cleaned the terminals, that seemed to help, but I noticed the lights would dim when I turned up the music or braked sometimes (just a bit) I upgraded to an optima Yellow top and it is all fixed. Car seems peppier.

95SC400

I had similar problems where the lights would turn off when I hit the brakes at night.

It ended up being the power steering pump/resevoir was leaking on the alternator (SC400) So I replaced the pump and rebuilt the resevoir and cleaned the alternator with a lot of alternator/degreaser cleaner. It has been a year now and the lights never act up.

DickLexus

My 92 sc400 has this problem. The high pressure power steering hose was leaking on the alternator. Everything went crazy, clock reset, engine bucked but not on a regular basis Replaced the hose for about $400. The alternator went shortly after, $500 . The coolant resevoir bottle went six months later racking up another $150. The coolant leaking on the alternator killed it again This was replaced for free by my mechanic(should be for $500). It is now acting up again but everything looks bone dry. Might have to try that negative ground cable replacement.

akmpres

if the voltage drop is 2 or 3 that could affect the starter from not starting and the clock to reset when i try to start it?