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I am trying to help out my Mother in Law. She has a 93 sentra. She had a dead battery so I replaced it for her. Before I did that the Brake and Alt light were lit. After replacing the battery everything seemed fine, nice charge, lights went out. Then when I went to put on the AC I heard the compressor kick in then a relay started clicking under the dash. When the relay was going on and off, the brake/alt lights were going on and off. If I shut off the AC the problem went away. If I left on for a minute or so the Brake/Alt lights stayed on again. This seemed to create a direct short. I removeed the battery from the circuit and the relay seemed to release and go back to normal operations. Question is, has anyone had this problem? Can anyone describe what relay might be cycling on and off? Any help would be appreciated.

Thanks
 

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Your electrical friend
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Well I pulled out my Factory Service Manual (Because I love this thing! worth every penny) and There is a wire from the alternator that makes it's way to the alternator dummy light in the dash, this same wire goes to a "bulb check" relay, which just so happens to connect to the brake dummy light as well, and the parking brake switch and brake fluid level switch. So three things could be causing the relay to flip out, causing the dummy lights to flicker. The parknig brake switch, brake fluid switch, or the alternator. My guess is the alternator, considering the battery went bad. This "bulb check" relay has the following wires coming out of it: A purple wire that goes to the instrument cluster and operates the brake dummy light. A black wire that goes to ground. A yellow wire that goes to the instument cluster in a different harness than the purple one, where it appears to go to all the dummy lights, probably to ground them. Lastly, there is a Yellow wire with a red stripe which goes to the alternator as well as the gauge cluster, where it operates the alternator dummy light (it's in the same harness on the back of the gauge cluster where that purple one is). This bulb check relay is located on the driver's side and I'm guessing it's one of the relays right next to the fuse panel. I'm going outside now to see if I can't figure out more.
 
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Wow, that is an answer. Remember it seems to be when the air conditioning is on. Could it be all the extra amp draw? With the bad battery yesterday I was getting about 12.9 volts at the battery with car running. Today i saw 14.2 when the battery was first put in and later about 13.7. Thanks
 

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Your electrical friend
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It'd be really easy to have an alternator check done for free at a parts store. Could save you a lot of trouble shooting time and her money, if she pays a mechanic to snoop around. I can't tell from looking if one of the relays next to the fuse block is that blubl check relay, but my guess is that it is. I know your A/C turning on is causing a problem, but I'm looking at it from the perspective, "what are the symptoms?" and that's where to start troubleshooting. But I'd have an alternator check done before I started spending any amount of time troubleshooting the electrical.
 

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its the alternator. i had the same symptoms 2-3 weeks ago and repalced the alt... all was good. that is until the ground wire broke 2 days later and caused my new alt to burn out. oh well... thank god for lifetime warranties.
 

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Yep, bad alt. Do yourself a favor though, and get one from the dealer. The aftermarket one's aren't remotely as reliable as the factory one.
 
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