74 Plymouth valiant died when headlights turned on.

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Johnnythunder

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Hi folks, I have a 74 Plymouth valiant 225 slant 6 auto. Before I bought it, my friend put in too big of an alternator and it burned up the wire to the ammeter. I replaced the wire and worked out the bugs over the last 6 months. I replaced the ECU then within a week it died, so I replaced the big alternator with the stock alternator from a wrecker, replaced the battery,voltage regulator, ballast resistor, coil, cap and rotor everything except the ECU because I just got one. It would turn over but not fire. So I got another new ECU,voila it ran and drove fine for a couple months, fast forward 2 days ago. Wife goes to start it nothing, battery is dead, so I charge the battery put fresh battery in and the brake switch was missing the pedal, keeping the lights on (the reason the battery died I think) I tweak the brake switch bracket now the brake lights are off, start the valiant, warm it up and I'm about to take off I turn on the headlight and instantly the car dies. Now it won't do anything, no click no dash lights no headlights,dead nothing, fuses are fine, but if I jump the starter relay it will turn over. I'm thinking shorted ignition switch at the key or some sort of short in the dash or cluster. I was thinking chewed wire from mice maybe, but the headlights worked fine till the other day...Any suggestions?
 
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Johnnythunder said:
Hi folks, I have a 74 Plymouth valiant 225 slant 6 auto. Before I bought it, my friend put in too big of an alternator and it burned up the wire to the ammeter. I replaced the wire and worked out the bugs over the last 6 months. I replaced the ECU then within a week it died, so I replaced the big alternator with the stock alternator from a wrecker, replaced the battery,voltage regulator, ballast resistor, coil, cap and rotor everything except the ECU because I just got one. It would turn over but not fire. So I got another new ECU,voila it ran and drove fine for a couple months, fast forward 2 days ago. Wife goes to start it nothing, battery is dead, so I charge the battery put fresh battery in and the brake switch was missing the pedal, keeping the lights on (the reason the battery died I think) I tweak the brake switch bracket now the brake lights are off, start the valiant, warm it up and I'm about to take off I turn on the headlight and instantly the car dies. Now it won't do anything, no click no dash lights no headlights,dead nothing, fuses are fine, but if I jump the starter relay it will turn over. I'm thinking shorted ignition switch at the key or some sort of short in the dash or cluster. I was thinking chewed wire from mice maybe, but the headlights worked fine till the other day...Any suggestions?
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Almost sounds like the battery terminals are loose, or a major short under the dash. I know I had the brake like switch ground out on the pedal before...terrible design on how those rely on pedal travel to work. you didnt kill the hot post on the starter relay did you? Idk what all uses that as a hot "bulkhead" if anything
 
Clutch sensor maybe. I had bent the frame on a truck. Picked up another one a year older. Then it died. After replacing everything in the electric side I decided to put my other motor in that was working and used at times to run power thru an over better before it ran out of gas and sat there. Slapped it in the other truck and nothing. Then a year later I start going thru everything again and got a hair up my ***. Took the sensor out of the truck that bent and boom it fired up. Now when I push the gas it bogs and does so I'm thinking fuel regulator cause I rebuilt and replaced everything else in the first gen throttle body. But hey I figured out I wasted my time swapping motors. On the plus side when I get around to it I should have that one running again. Man I miss driving that truck. Just glad I put in a slightly larger motor. Besides that sometimes those electric issues just kick u in the ***
 
Lol nevermind then. Didn't see that.
 
I'm going to go through clean and tighten all the grounds, then clean tighten battery cables. I read on another forum something about jumping the seatbelt interlock and the neutral safety switch. I'm just confused why it died via headlight switch unless that grounded or shorted out the ignition somehow, but after pushing the the headlight switch back in, the car remains dead as a door nail.
 
check the fuse link at the firewall sounds like it blew, or a bad ampmeter gauge. the volt ohm meter is going to be your friend on this one.
 
sealbelt interlock simply unplugs under the seat. no "jumper" required.

The NSS won't kill your lights and such. By "dead as a doornail" we're talking Nothing works? as if the battery is out, and on the ground? You indicate you can jump the starter...but is the horn, brake lights, dome light, etc ALL dead? Big difference in Zero power...and it simply not cranking via the Key IGN
 
Yes, fusible likely blown, fix problem first, or it will blow again.
Have you ever checked battery voltage with motor running? Problems with grounds, wiring or regulator, may lead to high voltage, burning out ECU. Killing engine with headlights may be electrical short to ground. That can happen in floor dimmer switch, does your car have that ?
 
Electrical problems can be a nightmare. It was not the the bigger alternator that was the problem. Current isn't pushed, it is drawn by a load. The lower the resistance, the more current is drawn. If somewhere there was a short to ground, you would have melted the wire. My advise is to find a manual such as a Haynes manual, and learn to read a schematic. It's just like playing connect the dots.
 
Dead as in dead. nothing works no horn no lights nothing, the only thing working is starter when I jump the relay. I'm an electrician, and I have the wiring diagrams for the car. I repaired a bunch of stuff already and the car was running fine untill the other day. Yes there is a floor dimmer switch. I was mostly seeing if anyone else on here had seen this specific problem where it died when the headlight was turned on. I'm probably going to pull the dash apart again, and go through the entire cars wiring. My wife loves this car so I'm going to do what I can. I appreciate all the help! I'm new on here and not much of an Internet guy, so it means a lot.
 
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