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Discussion Starter #1
Ok here is the problem. The battery is not being charged, the brake warning light and battery light are on. I took the alternator to O'Reileys to get tested and it checked out fine (14v) but I dont think they put a load on it. The alternator ground is good, S and IG both have continuity to the + terminal when they should. But I dont understand how the circuit to L works (what should I be checking for?). It seems the brake warning light gets power from the IGN fuse, and then L is acting as a ground then...? But why? And why is the diode needed? Can someone explain this cicuit to me in detail and offer any suggestions as to what my problem is?

Thanks....electrical shit is not my strong point. :)

 

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alternator needs to go on a VAT to do a true test..

here is what you can do. get a DMM and see what type of voltage the alternator is putting out at idle and at 2000 rpms with all your accerossories on.

what is the condition of tthe battery. most problem are in the battery. do a static discharge test, also do a surface discharge test. has the battery ever been dead before? i bet you have sulfate plates, then a battery won't charge worth a crap
 

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all the diode is for is to prevent fly-back voltage once the alternator kicks on. that's all. also check the ohms on both the battery cable. there is be little resistance.
 
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Discussion Starter #4
The battery should be fine. When I start the car, both warning lights go on the my TT tells me its seeing between 11.5-11.8v, so I figured the car is just running off of the battery. Can you explain to me how the battery warning light circuit works? I just dont understand it.

And when you say to check the resistance of the battery cables, from where to where?

Thanks for the help man.
 

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when you fisrt start your car, you should be seeing 14volts or at the battery
here is the deal. 12.65 volts is a fully charged battery
12.45 volts is 75% charge.

you are below both of those. also when a vehicle is running the battery should read what the alternator is putting out.

when the system is not seeing a correct voltage it will trip the dummy light.

also when the vehicle is running does the battery get hot?

if you are not seeing 14volts or more while the car is running it could be the alternator, but i'm not a 100% sure as i'm not directly working on yuor vehicle
 
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Discussion Starter #6
Well the 11.5-.8v reading is with a load on the battery (car running). With no load, battery voltage is at 12.5v.

Could the alternator put out 14v with no load but put out way below that once trying to power the car?
 

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If your only getting 12.5V with the engine running, especially with no load, your not getting alt. I had 14+ "with" a load and the engine running. If your alt checks out ok static test, your problem could be wiring. Check all your connections and clean them. If all your connections are good, it's your alt.

I had similar problems with dash lights when my alt went out. Even the nonpertinent lights came on.
I just replaced my brushes and all was well.
$13 from Toyota. That is provided your bearings are still good.
Takes less than 1 hr.
 
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Discussion Starter #9
Well I am getting 12v at S and IG but not at L. All fuses are good...... In the 87-88 manual, it shows L being fused through the 7.5amp CHARGE fuse and there is continuity between the alt and CHARGE fuse but none between the CHARGE fuse and the IGN fuse (across the brake warning light) WTF?
 

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just get a new alt....those stupid checks they do @ auto parts stores are useless....and be prepared to replace the alt several times- i've gone thru 2-3 "new" alts in order to find a good one....yea for lifetime guarantee! ;)
 
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