Electrical Help!

[TheJay]

Ok, I have this 1991 K5 Blazer, and i cant figure out this problem for the life of me. It has to with my battery not staying charged. When I drive it, the voltmeter that is in the dash will go up past 13 volts like its suppose to, but only when im accelerating from a dead stop(like when i pull out onto a road), but whenever im coasting, idling, backing up or anything else, my alternator wont charge my battery. I have replaced the alternator, the battery, Ive check all the connections i could think of and i even replaced the wire that goes from the alternator to the battery.I had my alternator tested at an AutoZone. I cant drive for more than a few days without getting a dead battery. this sucks because until i can fix this problem i have to hook my battery up to a charger twice a week. I cant keep doing that. If anybody has any ideas or solutions, please fill me in!

[krue]

Welcome to the board from South Mississippi! I would have my alternator checked somewhere besides AZ, preferably an auto electric shop, have the battery checked also.

[Tink]

If your alternator and battery check out, I'd say you have a short somewhere causing the drain... we had a 96 S10 that had been wrecked and after it was fixed it would drain the battery every few days due to some wires that had been pinched in the accident and the coating was removed... the bare wires contained a hot feed and it was shorting out causing the problem.

[Zoomad75]

I'm betting you have a draw on the system discharging your battery. The battery is getting pulled down low enough that it's maxing out your alternator. Most stock Alternators don't charge well at idle speeds...

Here's a reason to add to your Tool collection if you don't have it. Get a digital volt/ohm meter. You can get decent ones at Sears or Harbor freight or even some of the chain parts stores. With the Meter you can isolate the circuit that the draw is coming from. If you don't want to buy one, find a buddy and borrow one.

Once you have one, disconnect your positive battery cable. Connect your test leads from your meter, one to the positive post of the battery, the other to the now diosconnected positive cable end. Switch your meter to AMPS, low scale. *****IMPORTANT NOTE: Keep the key in the OFF position and DON'T attempt to start the engine with the meter hooked up, you will overload the meter.****** With the key off, look at how many amps is being drawn. Ideally, with no draw it should be 0, but you have EFI and most likely a digital radio (memory) so you will have some draw of less than 10 milliamps. If you do have a current drain of more than that showing, go inside to the fuse block and start pulling fuses one at a time. Each time, check the meter to see if the drain went away. Do this until the drain is gone. Once you have found which circiut the drain is coming from, you can diagnose futher as to why it's staying on or active with the key off.

I'd start with any aftermarket accessories first. Could be an amp (if you have one) staying on or a light staying lit overnight. Could be anything, but if you use an organized process to diagnose it, you should find it.

[motopatzo]

It does almost sound like a draw, but I don't understand why the voltmeter only shows just over 13 volts? Normal charging voltage should be around 14 volts at idle and slightly higher while driving. I would have the charging system load tested at idle and at about 2000 rpm to check what your alternator is putting out. Depending on the alternator, it should at least put out anywhere from 60 amps to 100 amps. Also have the battery load tested, to eliminate any possibility of another bad battery. And......have you checked your chassis and engine grounds?

[TheJay]

Ok, I got a hold of a multimeter and checked the amperage from the disconnected positive terminal...it was at about 37 milliamps...i then went ahead and checked all the fuses one by one and on the last one it went down to about 6-7 milliamps...i think im a step closer...the fuse went to "STOP-HZ" and i have no idea what that means...i looked at a wiring diagram and the wire that goes from that fuse goes to another pannel that stops with the letter "P" and says "stop light switch" next to it...a friend of mine told notified me that i had a taillight out a short ways back...could the taillight and the problem with not charging be connected somehow?...and the fuse in the box was a 20 amp and it says it only requires 15 amp, so somebody made that change before i owned this truck...could that have anything to do with it? as in..since the fuse is of a higher rating perhaps that extra 5 amperage leeway caused some wire to fry?...im not that great with this stuff, as you guys can tell.

[krue]

Stop-Haz is your brake lights/emergency blinkers. Change the bulb, I guess it's possible it could be shorted.

[Bandit76]

Stop and Hazard Light circuit. If the multimeter can measure ohms, check with the battery disconnected, both sides of the fuse holder to ground (with the fuse out), but most importantly you are looking for the non-supply side of the fuse.

The feeds to the fuses for brake lights and hazards circuits (2 circuits) are hot at all times, not switched power.

Volts = amps x resistance

12 Volts = 15 Amps x 0.8 ohms. as an example.

Measure everything to ground.

With the fuse and the bulbs out you should be able to find it. The fuse will have one side from the supply and the other side will feed the circuit. The wire between the fuse and the bulbs should all read infinite ohms or OL or open loop. If there is a short to ground it will register a number.

Just remember path of least resistance. That's where it'll go if it can.

One side of the bulb holder should be 0 ohms - connected to ground
The other side will be coming from the hazard relay.(maybe faulty relay - corroded contact)

The hazard relay/turn flasher actually turn the lights off when they switch.