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Alternator Wiring question

2K views 8 replies 2 participants last post by  docvette 
#1 ·
On a '65 Mustang, does the wire to the alternator "BAT" slot come from the wiring harness, or straight from the solenoid? My wiring diagram is weird. My battery went dead after a year of use (but I don't know how long the guy before me used it or how new it was). Cleaned all my wires, reconnected everything, quick re-wire. Replaced some almost shot wires, and everything. The lights used to get bright when I accelerated and then dim again, and it doesn't do that anymore. Stuff like that. When I used the wiring the way that it was set up, which was straight from the solenoid, I tapped the battery cable to the battery terminal, and it sparked like a bastard, so I pulled the wire, disconnected it from the solenoid and the alternator, started the car and it runs fine. My question is should I get a new wiring harness? Or am I in good shape? The alternator light doesn't come on, and the car starts great, and runs great.

*Edit* Also, what's the difference between an alternator with lamps and one with gauges? The wiring loom is only 20$.
 
#2 ·
Doc here, :pimp:

One procedure at a time.... :smash: :sweat:

The BATT wire (10 gauge) goes to the battery side of the solenoid.

Why the battery went dead could be about anything from leaving a lamp on and forgetting about it to a bad set of diodes in the alternator.

Sounds like you did the right thing on the wiring harness..clean and replace as needed.. :thumbup:

Sounds like in so doing, as evidenced by your better lighting, you cleaned up some bad grounds and some bad wires. you may have been under charging before contributing to the dead battery.

On the solenoid, If when you connected the battery cable you got a big spark..you have a major system draw..How did you start the car with those off the solenoid? In theory, It should have no power anywhere... :confused: :confused:

If it only sparked when you hooked up the Alternator to the solenoid, you either have the wrong wire from the alternator, or a short on it, or the diodes on the alternator are totally shot..

Again, another mystery, If you disconnected the Alternator and drove it, and the lights got Bright, and stayed bright..and the alternator light is out..how did that happen? :confused: :confused:

I'd find out if you have a problem in the harness before you go replacing it..may just be a waste of money if the diodes are shot..better spent on a rebuild kit or new alternator.

You need to do a current draw test with the alternator in circuit, and one without to determine if it is that or another draw in the car..Get out your DVOM, and set it for AMPS , Highest scale, with everything hooked up, remove either battery cable, place one probe on the battery and the other on the cable that was there...

scale the AMPS scale back until it almost pegs the meter, that will be your reading..It should read between 0.3 and 0.8 amps on a modern vehicle with a Computer, CD player with memory presets, Clock, and mechanical clock..any more and you have a draw that is causing a dead battery..

If so, disconnect the alternator, re~take your readings..If the load drops into the 0.3-0.8 range .. your alternator needs service, or replacement.

If not , hook it back up and go to your fuse box, If it is well identified as to what fuse is what, pull all the fuses..If it is not make a drawing of the fuse layout and fuse values then pull them all..

Re~take your measurements..t should be 000..If so, Check all the fuses (with an ohm meter set to R X 1 Scale, calibrated to 000) and replace them in the fuse buss one at a time in proper sequence..

re~take your Current draw after each fuse is put back, until it shoots up past the 0.3-0.8 range..that will be the offender..follow that branch circuit and clear or remove the draw.

Doc
 
#3 · (Edited)
On the BAT part of the alternator, there was a big rubber seal and a nut. Should the seal be between the cable end and the alternator, or on top of the cable, allowing the cable to go straight to the alternator? It only sparked if the cable moved a little bit, causing it to touch the alternator. I was thinking that I should put the seal on the stud coming out of the alternator, then the cable end, then the nut and bolt it down that way? Is that why it sparked? The only cable that wasn't plugged in when I went to start the car was solenoid -> alternator. Am I correct in thinking that the rubber should go first, then the cable, and then the nut? Also, there are a few stripped/coming apart wires in the harness, and I intend to replace it in the near future anyways. This alternator is brand new from NAPA auto parts.
 
#4 ·
Doc here, :pimp:

If you mean a BIG rubber boot, that would cover the terminal and wire with a hole for the wire to come into it, Yes It goes on top of the wire and terminal to keep tools from shorting it out.

However if you mean a round rubber/plastic washer that slides over the terminal, then No it is an insulating washer to keep the battery terminal from shouting on the alternator body..(a dead short from the battery cable to ground) If thats the case..you have a major short that is occurring from the alternator body to that Battery feed wire and will cause a melt down or fire..

If you had a fuse link on the alternator and Buss support lines It would have burned open to protect the wires..however, Vehicles of that vintage did not..unless someone installed one aftermarket.

If the latter occured..lack of an insulating washer and intermittent shorting was happening , your alternator MAY be toast..You'll need to correct the problem and test.

Doc
 
#8 ·
Sorry I haven't reposted back, I haven't been home in awhile. Had lots of places to drive to. =))) I put the wire from my solenoid to the alternator battery terminal, with the plastic under the end of the wire, and then the nut at the top. Started up with a bit of hesitation, then drove around, stopped, and started it again, no problems. Haven't had a problem since. All the grounds are good, everything's running smooth as hell! Thanks for your insight Doc.

~65
 
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