hemidog

i have a 70 challenger that i had a short that melted the engine harness wire & the dash harness. i have replaced both of those harness's but the short is still there. i have eliminated the coil,distributor,alt,voltage regulator,ballast resistor, and all the plugs in the dash. with the ign key turned on if you remove 1 of the field wires from the alt it arcs like there is a dead short. if i unhook the dash pwr & gnd wire at back of voltmeter it dosent arc but none of the interior electical works with this disconnected including the ign. i am wondering if its the ralley dash gauge ***. any ideas?

440roadrunner

Put a "big" test lamp in series with the battery ground. This will not only light up with current draw, but will limit current so that nothing else will burn up.

I'm not intimately familiar with Challenger wiring, but like most Mopars, there's a certain amount of "stuff" that does not go through the fuse box.

You need to isolate the problem into sections

One BIG thing you have not mentioned is "did you" disconnect the main alternator output terminal? Several kinds of problems internal to the alternator can cause heavy draw or a dead short.

Also, NOTHING in the ignition "run" feed is FUSED, except for th emain fuse link.

It IS normal for the alternator field to show a spark with KEY IN RUN and then disconnected. The (incorrectly called) "dual field" or "isolated field" works by feeding switched 12V TO the alternator field through the blue field wire, and then the regulator (green wire) controls the ground leg of the field. With key on, the field is drawing full current, as the regulator "thinks" it needs to charge. The regulator "has no idea" that the engine is not running.

Things the ignition feeds on the run wire:

Up in the cluster, it feeds power to the gauges "voltage limiter," to the warning lights such as oil (if equipped) and brake warning light. It goes out through the bulkhead and feeds

ignition system

alternator field

regulator IGN terminal

distributor retard solenoid if equipped

electric choke if equipped

Idle solenoid if equipped

In some years, one or two other "smog doo dads."

The headlight switch power for ONLY the headlights is not fused, either. This power comes off the splice in the black ammeter lead right over to the switch, and there's a breaker in the switch.

You have a shop manual? You can download a 70 Plymouth manual for free over at MyMopar, but you have to argue with page numbers.

If you can give me a SPECIFIC list of what you have disconnected and the results, I can maybe give you some ideas

MyMopar tech stuff

http://www.mymopar.com/index.php?pid=31

70 Plymouth manual (use the 'Cuda info)

http://www.mymopar.com/downloads/ser...ice_Manual.zip

Also "over there" are somewhat simplified diagrams, not always correct and not always complete, but sometimes easier to follow for certain problems:

http://www.mymopar.com/downloads/1970/70ChallengerA.JPG

http://www.mymopar.com/downloads/1970/70ChallengerB.JPG

Another common problem with alternators is that BOTH of the field terminals, with the wires disconnected should NOT show continuity to ground. This is a common problem with rebuilt alternators, and sometimes the brushes/ insulators break and ground out

The gauge you unhooked in the dash is an AMMETER, and this has ALL current going through it in series. The power path is something like this:

From battery, to starter relay stud, to fuse link, through bulkhead, to ammeter (on red wire) through the ammeter, then the black wire goes out through the bulkhead and connects to the alternator. IN THE BLACK WIRE taped up in the under--dash harness is a factory "welded splice." Power branches off of this to feed off to several places

To the fuse panel "hot" buss

To power INTO the ignition switch

To the headlights

I almost forgot, here's a BETTER manual for you, posted by AbodyJoe over at FABO

70 Dart/ Challenger manual:

http://www.abodyjoe.com/pictures/Mis...erv%20Man1.pdf

On page 8-89 of the above document, find the "N" terminal of the bulkhead connector, which is the Dark Blue ignition feed. It's toward the bottom right of the page to the right of the A/C compressor. If you follow that, you'll see what it feeds under the hood.

If you look on page 8-94, very top, find the ammeter, and follow the red wire (A1-12R) down the page you'll see it goes to the bulkhead connector. This is ALL power coming INTO the interior, and it goes through the ammeter, out the black and elsewhere The ONLY thing protecting this system is the main fuse link out by the starter relay

Now follow the ammter black (R6A-12BK) off the page and down into the left side of the next page

You'll see that it goes to a big splice with about six wires

J1-12R goes off the page, back up a page, and feeds power to the ignition switch

R6-12BK goes back to the bulkhead connector and to the alternator output stud

L1-16BK goes up and to the right of the splice and feeds power to the headlight switch. This is HEAD power only---tail, park, and dash lamps are powered from a fuse in the panel

Q3-14R (a misprint should be no12) goes down and feeds power to the "hot" buss in the fuse panel. This is everything that works with the ignition off, such as brake lights, dome, etc.

H1-16V goes to the right, and feeds power to the horn relay NOT FUSED Pull the relay out to test.

RacerHog

I agree....Test light in the ground side... And start unplugging...You will find it when the light go's out.... Just dont leave the door open with the dome light bulb in place.....lol
Dont ask me how I know......lol

hemidog

thanks for the info i havent had time to look at it any further yet

RacerHog

Keep us posted...

hemidog

1 of the alt fields was shorted to the alt case. no more problems with a short but now the am meter shows full charge all the time. i checked alt output with a clip on meter shows 15 amps at idle. i checked at both wires on back of ammeter shows same as at alt. i checked the resistance of meter shows 0 ohms is this correct

RacerHog

Awaaaaaa.... That would do it...

Even At Idle?

hemidog

yep even at idle but its not over charging the battery.

440roadrunner

Sure it is, you just haven't run it enough.

First do you have a correct alternator?

Should have two "push on" field wire terminals.

If it's a "round back" take it back and demand a "square back" The square backs are better alternators. Many roundbacks have been converted by shoddy rebuilders. Either type, though, can have a grounded brush. If you happen to hook the blue field wire to this incorrectly grounded brush, you'll burn up some more wiring, or at the least, a fuse link.

This thread shows some variations in the older "roundback"

http://www.forabodiesonly.com/mopar/...d.php?t=211497

THIS is the desired "squareback" on the LEFT


Remove both field wires. Take an ohmeter and check continuity from both alternator field terminals to ground. Neither should show continuity to ground.

Make ABSOLUTELY certain that the regulator is grounded. Remove the regulator, scrape the flange and firewall, and install using star lock washers.

If that does not cure it, make sure that the regulator wiring "has control"

To do that, disconnect the regulator connector and run the engine. It should NOT charge.

If it stops charging, check for voltage drop. To do that, turn the key to "run" with engine shut off. With everything hooked up "normal" check battery voltage and then check voltage at the blue field wire WITH IT CONNECTED to the alternator field. The two voltages should be very close, within .3V (three tenths of one volt) of each other. If it's some what more, you have a harness voltage drop problem.

If that checks out OK and it still overcharges, replace the regulator.