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Discussion Starter #1
I've been chasing my own tail on this problem for a couple weeks now and am hoping I can get at it a little easier by asking everyone here. The problem that I am having with my Ranchero is that whenever I press the breaks the car experiences a noticeable drop in voltage and can sometimes drop far enough that it will completely die on me unless I'm prepared for it and am "2 footing" it, the problem is made significantly worse at night when I have the running lights on. The battery is about 4 months old, I just replaced the headlight switch (cleaned up part of the problem thankfully), the alternator is about 9 months old (a 65 amp deal), and I also have a new starter solenoid that I installed at the same time as the alternator. I replaced the voltage regulator earlier today but that didn't correct the irregular voltage so now I'm on to chasing wires!

Before I got the car running I ended up having to get at the wiring harness under the drivers side of the bench seat because a previous owner decided it would be a good idea to mount an amp under the drivers side of the bench seat and just so happened to punch right through the entire harness with a power drill going to the back of the car (patching all 6 of those 3/8" holes was enough to make you cry on it's own). I repaired that using bullet connectors, lots of electrical tape, and putting a new harness jacket around it from the firewall all the way back into the cargo cubby behind the seat. I'm fairly certain that I will have to take the seat out again and re-do the repairs to the harness as it may be what is causing my voltage problem, I'm also gonna take the alternator in and have it tested just to be extra sure that that is not the problem.

Any other ideas would be greatly appreciated as well :)
 

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Does it do it sitting still in Park? Any amp draw high enough to pull the engine down should be blowing fuses. The only electrical thing that should be happening when you press the brake pedal is the brake lights.
 

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I am 78.9493111117% sure you simply have Grounding issues between the frame and body and battery.

Grounding issues in a 67 Stang I had back in the 80's in Denver were just like that! Double foot it or die and be embarrassed. One day I saw a spark on the firewall when cranking. It was a ground strap.... Then I re-did ALL the grounds and doubled the body to frame grounds and all was well.
 

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X2 on the grounding. I run a big ground wire right to the block then off the same bolt another big one to the frame. Then I have multiple smaller ones in various other places. Can't have too many.
 

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I fully agree with grounding being the #1 gremlin in our cars. You can't have too many and they can't be too clean. But drawing enough power to kill the engine is almost unimaginable. At that level, you should have smoke in the cab. Do you have power or manual brakes? If power, double-check that you don't have two issues simultaneously, such as a bad brake booster. A bad booster can leak, causing the engine to go lean, causing rpms to drop, but that also causes voltage to drop with the slower alternator. It can become a self-feeding monster, killing your engine every time you step on the brakes.

David
 

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Discussion Starter #7
Well the alternator came back defective so I swapped it out on warranty and after a run around the block with everything on the car ran like a dream! I'm still gonna get in there and clean all the grounding connections and double check the repair work under the seat but all said and done I'm glad the worst of it is over.
 
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