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unexplained electrical problems


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6 replies to this topic

#1 girven

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Posted 19 September 2004 - 09:49 AM

Hi, brand new to the site so taking the time to say what a great board full of useful info.
bought a 89 gl a year ago for 300 bucks and with new timing belts, water pump, radiator, brake cylinder,and winshield have a very dependable car, all said about $800 wrapped up into it and it passed PA inspection with flying colors.
anywho, my problem. jumped in to go somewhere and the battery was dead. jump started it and checked the voltmeter and it read about 10 volts.
put the multimeter on the battery posts and got 12.5 volts. turned the car off and got 11.?? something on the battery. checked the cells on the battery and one was low on water, filled it and charged. same thing. put new battery in. now i get 14.5 volts at the battery but at idle i get 12 on the meter in the dash. turn the lights, wipers, fan on and drops to about 9 but still have 14.5 at the battery? at night lights dim and then all of a sudden get bright then slowly dim etc... any ideas what is going on? alt bad? bad wire to the fuse block? I'm stumped. any help would be appreciated. thanks

#2 edrach

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Posted 19 September 2004 - 10:56 AM

I would think a bad or loose connection somewhere. Check both battery cables and connections.

#3 Cougar

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Posted 19 September 2004 - 01:21 PM

Welcome to the forum Girven. It's good to have a another Soob family member here.

It does seem you have a loose connection somewhere as Edrach stated. I think you are seeing the dimming as a result of a bad connection that heats up from the current draw, and as the resistance goes up, so does the voltage drop across the connection. This means less voltage getting to the device.

If you haven't cleaned the battery connections with a cleaning brush I would recommend doing that. Also check the fusible links in the plastic box mounted on the coolant reservoir above the left front wheel. These connections are a common problem. Be sure the contacts are tight and clean. If that doesn't help then I would check the main accessory power lead (smaller wire) from the positive battery connection for internal corrosion or bad contact. There may be a bad ground causing this but this sounds more like a bad power lead connection.

If these things still don't help then use your meter to find the drop. You may first want to check the voltage between chassis ground and the power to the fuse panel. If it is low, move the meter ground lead to the negative post and see if you have close to the same reading. If so, then you know the problem is in the main positive feed line somewhere. Keep moving back towards the battery until you find the proper voltage. Since the fusible links are the main connections that can cause this kind of thing, I think you will find the problem there. It also could be a bad power relay though. Checking the voltage drop across the contacts will show up any problem there.

It's good to hear you have a meter. It's one of the best pieces of test equipment you can own in my book.

#4 girven

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Posted 19 September 2004 - 03:33 PM

thanks guys, i checked the connections, clean. checked the voltage to the fuse box... getting 13.6. checked the fusable links getting 14.2 on both sides. w/ the engine running i unplugged the wiper motor and checked that and got 13.6 there. but when i turn the lights on wipers, fan i get a visable drop on the dash lights and i also have driving lights i installed, when i turn those on the radio turns off for just a sec then turns back on and the lights dim as well. the only thing i didn't check was the power relay, don't know where it is. maybe that's the problem? still perplexed

#5 Cougar

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Posted 19 September 2004 - 03:55 PM

When you say the lights dim, does this mean the headlights along with the dash lights? You may have a ground problem after all. You could try making a ground jumper lead with a 14ga. or larger wire and connect one end to the ground post of the battery and the other end to suspected bad ground spots and see if things change. It's sounding like there may be a bad ground at the dash and/or the ground to the body frame. I think there is a frame ground behind the battery that is a common problem.

When taking measurements do them with the load connected so you will be drawing power and be able to see the voltage drop. Removing the load will reduce the drop.

I just checked my manual for a '88. It appears that the returns for the headlights go back to the headlight switch in the dash and are grounded there. This would really make the dash ground suspect. The return wire color is red/black. You could measure the voltage at the headlight to battery ground and see if you have a drop across it while the lights are on. If you do, then you need to check the dash ground and at the light switch.

#6 girven

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Posted 19 September 2004 - 04:22 PM

cougar, thanks that seemed to be the problem, I made a jumper wire and grounded to the strut tower ground. turned all acc. on and volt meter never dropped below 12. even when i turned the driving lights on. awsome
thanks, thanks, thanks!!!

#7 Cougar

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Posted 19 September 2004 - 04:31 PM

Good work. I would try to find the bad gound connection and repair it. It may just be loose. I added to my previous post some new info. Check it out if you haven't already.

Your welcome for the help. Drive on!




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