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Discussion Starter · #1 ·
Here's the deal.

The volts are fine at sit at 14 volts with EVERYTHING on... untill the breaks are de-pressed.

Then they drop to 10 volts.. by everything I mean int. lights, ext. lights, and heater fan.

The fan motor pitch changes (sound) as it sounds like it slows down.

This only happens wtih the headlgiths on though.. turn them off, and the voltage is fine.

I checked the lights tonight.. theyre off until the pedal is depressed, then they go on, they go back off after the pedal is released.

I checked the belt tension and alt mount.. both good.

I was just going to let this slide until it gets a bit warmer or I get home to a heated shop.. but no such luck.. there's been Vehicle Inspections like crazy around here and I don'twant to find out the something lights aren't working the hard way... with a VI.

The draw drops the volt meter to 6 when I crank her on the starter...

This also just started recently... in the last couple days.

I also have a feeling I'm not getting all my rightfull spark when this happens because the engine was doing some crazy arse crap on the highway tonight.. (thumping)

ANy help is appreciated.
Thnx folks.
 

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how are you checking voltage?? With a good meter, or reading the cheasy meter in the dash?? I know you say the fan bogs down and such, so there is a voltage drop occuring somewhere, but just wondering how accurate you are on how much it drops. I guess it really doesn't matter, because a drop is a drop.

And just to check, this only happens with the engine running, with the headlights on, and when you step on the brakes?? So, headlights off, step on the brakes, no problem??

I am just trying to better understand the symtoms here.... oh and I am by no means an electrical wiz either...
 

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Discussion Starter · #3 ·
Yup..

I drive to school every morning with the fan.. and it was fine..

I drove home with the lights and fan.. and it bogs.
I drive home with the lights, it's fine...

I'm going to get a real meter on it.. its just kind of hard to read one while I'm driving..

It seems to me like the breaks are being the "straw that broke the camels back" and are just pushing the whole system over the edge.. but the blinkers make the needle move.. only it moves 1/2 volt and then back up..

And I've got a set of rocklights made from KC day lighters.. and with the headlights, fan, and rocklights.. I get just under 14 volts and no bogging..

It's almsot like there's a short in the break lights, and when they are on, they are shorting and draining the system..

I assume they are on a relay? (89 YJ) does that sound like a possible?

I'm electric dumb here.. I can chase gremlins.. I just don't get this one.
 

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In reply to:

but the blinkers make the needle move..

[/ QUOTE ]

I don't have any of the problems you have except this one. The volt meter moves back and forth in unison with the blinker down to about 10 v. It's done is since I got it.
 

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1. Check the grounds.
2. The electrons have:[*]Get to the device [*]Then return back to the battery
3. If the grounds are compromised...
4. You'll get what you're seeing.
5. Look at the grounding for the blower motor...
6. It grounds to the tub via the heater box,
7. I welded on a grounding stud to the blower motor case,
8. and ran a separate ground...
9. The lights ground via wires to the grill,
10. The grill grounds via bolts to the tub.
11. If the grill/tub ground is compromised,
12. Then the voltage will drop as the lights are put on.
13. I'd suggest running a temporary battery ground to the lights,
14. Remove the grill ground...
15. Then see if the voltage drops,
16. If it doesn't drop, that's the problem...
17. If it does drop... we keep looking.
 

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Yes, sure sounds like grounds.
Easy way to check - use battery jumper cables - one end on the engine, the other to good body grouning points. Check it at several places. If the problem goes away, ya got it.

And - it could be resistance in the main power source - the wire to the fuse block from the starter solenoid - loose, frayed, broken etc.
 

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IMHO... I can't reason how this problem would be caused by a bad ground. If his ground was weak then it would present a larger resistance to the battery resulting in less current flow through the device. Less current flow means less stress on the battery but poor performance of whatever electrical device has the bad ground. On the other hand, if there is a short somewhere in the electrical connection to the brake lights when the light switches on a smaller than normal resistance is presented to the battery and more current will flow. This requires more power (V*I) from the battery. Too much and the battery voltage will drop. What's wrong with this analysis?

Lee
 

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A bad ground can act the same as a bad connection on the hot side. Whatever current can flow, it goes through both the initial feed wire, then back home to the battery through the ground - a complete (closed) circuit. If an unwanted resistance is in that circuit it drops the voltage available for the wanted devices. If resistance in the circuit is excessive, it drops the total current. Unfortunatly all the other components also share that same ground path and feed line.

Sooo - lights on, blower on, a specific amount of current is flowing - the unwanted resistance is lowering the current, but not enough to notice -- yet. Then hit the brakes, the brake lights draw another 10 amps or so, the currect tries to go up, the drop across the unwanted resistance goes up, so the other devices get starved even more.

Another way to look at it is not the brake lights - they are fine - but while the lights are on and brake lights on, turning on the blower dims the lights. That's why I doubt it's the brake lights shorting to ground (they are OK with the blower off.) It's dependant on the total current to all the devices - common to everything.
If a big heavy stereo was connected in that circuit and turned up loud, you'd see the lights flicker to the boom, boom, boom as well.
He He - picture trying to drive down the street with the ignition cutting out to the tune of Hello Dolly!

 

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Ahh... now I see were you're coming from. If that's the case then he should be able to put a voltmeter directly across the battery terminals and measure 14-Volts (whatever his typical battery voltage is) since the voltage drop is external to the battery in the loop. Correct?

Another thought (not really pertaining to the problem at hand)... If the alternator had a bad ground I guess this could throw off it's regulation and cause a lower than desired (<12V) system voltage. Do you agree?
 

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Yes, and Yes.

Actually if he were to measure right across the battery he should see the full battery voltage - from 12.6 to 14 or so, depending on surface charge.
Then - getting creative - he could turn on the accessories mentioned, light, brake lights (a brick on the pedal), ignition and blower. Should still be the same at the battery - maybe just a tad less.
Now move the voltmeter (-) lead to the main fuse box or central power distribution point. Should say near 0 volts, as you are simply measuring along the feed wire. If more than 1 volt, the resistance is in there. Sometimes factory splices go bad - hard to find.

Then put the (-) voltmeter lead back on the battery.
Move the (+) voltmeter lead to the dash ground, then body ground etc. Again, if any reading is found, it's the ground problem. You can isolate where the connection goes bad. Measuring along the ground from the battery (-) should be 0!

The alternator is pretty hard to get a bad ground itself, as it's mounted directly to the engine with - hopefully solid brackets. But a bad ground between engine to body is very common and creates all kinds of troubles.

1. The battery (-) terminal should have a heavy cable to the engine block.
2. There should be a good ground strap between the body to the engine.
3. Another strap from the body to the frame.
All of those points, engine, body, frame, have various electrical devices, but are normally isolated from each other by rubber - engine mounts, body mounts etc. They need a good electrical tie in.

Sometimes body panels just bolted together aren't a good enough ground - rust, loose etc cause resistance. When in doubt, bridge the joint with a strap.
The flat ground straps available at the parts houses are designed to flex billions of times - they use tiny strands of wire woven into the strap, a stranded wire isn't made to flex that much - it breaks soon.
You can't overdo the grounds. Too many won't hurt, one missing will.

Just remember - a resistance in the feed wire, or ground path, is a series resistance with the rest of the load.
 
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