I have recently developed a problem with 3 dash lights randomly coming on and then shutting off, and sometimes just flickering. The 3 lights are the Brake light, the Tail Light light, and the battery light. When the lights come on nothing seems to dim down all my exterior lights stay on, and nothing seems to be wrong. The lights all always come on at the same time and shut off at the same time. Any possible answers would help. THANK YOU
Help with dash lights? Brake, Rear lights and battery light
- Thread starter boosted_mkIII
- Start date
i had a similar problem. all three of these lights would come on and stay on. Mechanics did not know why. battery would be fine but would go dead after a week or two would go by and if i did not crank the car.
looked at the wiring diagram and all three of these lights have a common ground. turned out it was that the diode in the alternator was bad and allowed current to flow backwards thru the ground and grounded out at the positive side of the wiring. remove the alt and have it checked and i bet you will find it is going out or is out. i knew when i had this problem it wasnt my alt because i had just bought it 3 weeks before but it was a bad unit.
looked at the wiring diagram and all three of these lights have a common ground. turned out it was that the diode in the alternator was bad and allowed current to flow backwards thru the ground and grounded out at the positive side of the wiring. remove the alt and have it checked and i bet you will find it is going out or is out. i knew when i had this problem it wasnt my alt because i had just bought it 3 weeks before but it was a bad unit.
Yes, those three lights are meant to come on when the alternator is going out.
Replace the alternator and it will go away.
Replace the alternator and it will go away.
My alternator tested good on and off the car, and this exact same issue stopped yesterday right after my blower motor failed. Do you guys still think it's the alternator, or was it a case of something in the blower motor circuit, like too much current draw, causing the warning lights to flicker?
Flickering came back. 
Didn't find any problem when testing the cables from the alternator to the battery or from the battery to the ground on the fender. Alternator tested good again as well. Going to check the connections on the starter soon to see if they are loose. Any other places/things to check? I'm not ruling out the alternator, but I want to rule everything else out before replacing it.
Didn't find any problem when testing the cables from the alternator to the battery or from the battery to the ground on the fender. Alternator tested good again as well. Going to check the connections on the starter soon to see if they are loose. Any other places/things to check? I'm not ruling out the alternator, but I want to rule everything else out before replacing it.
Still flickering randomly. I can sometimes force it to happen when there is a draw on the system, like when I hit the brakes or use the window motors. I've retested the alternator numerous times and even swapped a known good one on, but it still does it. Grounds all look good as well. I'm guessing it's something either behind the dash now or some other electrical gremlin. What makes this hard to test is if I shut the car off, the problem goes away on the next restart for a good 5-10 minutes at minimum, even if it they had been on for a solid 5 minutes as I parked and shut the car off. Also, as far as I can tell, there is no drain on the battery after 24hrs of sitting. It's like there is a ground short somewhere, but again, all of the grounds look fine and are tight.
Oh well, I have more pressing issues. I have to replace the cam cover breather tube now and figure out why the car has decided it wants to burn a quart of oil every 1000k miles or so.
Oh well, I have more pressing issues. I have to replace the cam cover breather tube now and figure out why the car has decided it wants to burn a quart of oil every 1000k miles or so.
Oh yeah, already did all of this.
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=CH&P=2
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=CH&P=2
Gauge drops from what appears to be about 14v to 12v when the lights come on. (edit: of course, on the rare occasion they stay on for more than a few seconds, you'll notice the voltage continue to drop). Instantly goes back to 14v when they go off, so the alternator is charging.) Multimeter reads roughly the same as the dash voltmeter.
It's been a few weeks since I last did the testing in the link above but I recall the voltage across the terminals, from the alternator to the battery, and the battery to ground all showing normal voltage readings. I checked the engine and trans grounds when I had the tires replaced a few days ago. The rear light bulb sockets has some corrosion causing the failure lamp to come on occasionally, but that stopped when I cleaned the failure module, the bulb sockets and replaced the bulbs about a month ago.
One thing that may be just coincidence, but the dash lights seem to come on more frequently while/after braking or when the lights are on. Maybe there is a break in one of the wires that run to the alternator's harness. 22 years is a long time.
It's been a few weeks since I last did the testing in the link above but I recall the voltage across the terminals, from the alternator to the battery, and the battery to ground all showing normal voltage readings. I checked the engine and trans grounds when I had the tires replaced a few days ago. The rear light bulb sockets has some corrosion causing the failure lamp to come on occasionally, but that stopped when I cleaned the failure module, the bulb sockets and replaced the bulbs about a month ago.
One thing that may be just coincidence, but the dash lights seem to come on more frequently while/after braking or when the lights are on. Maybe there is a break in one of the wires that run to the alternator's harness. 22 years is a long time.
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Its pretty obvious what your issue is. But it seems you need to prove it to yourself. So try this test with terminal F, while it is acting up. That should lead you down the right path.
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=CH&P=5
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=CH&P=5
mkiiichip;1774916 said:
Thanks for the link. I didn't see that one before, but I'll check it out.
And don't think I'm being stubborn because I enjoy it. I'm living off my savings while I'm back in school full time so the thought of buying a new alternator is pretty low on my list. Besides, the alternator was replaced less than 5 years/30k miles ago and, in my experience, when an alternator dies this soon after replacement it is caused by something external. Found this out going through the old service records.
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hey guys, just had this similar issue before reading through this thread haha! anyways i left work with my new copper plugs installed, seeing if it cured my break up issues. after a nice smooth pull i noticed that my brake, rear lights, and batt. lights all came on, thought this was a little weird.. anyways they seem to stay on all the time UNLESS i rev over 3,000 rpm's.. going to test my alternator tomorrow at work and hoping its bad, that would be a simple fix. curious if anyone else had any other fixes for this issue or if all fingers point to the alternator.
You can try replacing the brushes first. Its pretty easy on this alternator.
http://www.supramania.com/forums/sh...rnator-issue&p=1818937&viewfull=1#post1818937
http://www.supramania.com/forums/sh...rnator-issue&p=1818937&viewfull=1#post1818937
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I think it's the diode going bad and allows current backwards through the ground which turns on the lights. All three of those dash lights are grounded to the same spot in the diagram.
Halsupramk3;2018807 said:
I'm not sure how you conclude that. The charge light (and the other two lamps in the combination meter) connect to the L terminal of the alternator. Why do you think the L terminal is a diode? Its actually part of the voltage regulator in the alternator.
As a side note, the rectifier assembly in an alternator has multiple diodes.