Blows the running light circuit

[Mopar Tom]

Hey guys ,,just got Mopar Jr.  (my 16yr old son) a car--well he put up $3000 of it ! 67 Coronet 440 -727-440-all stock--rust free-- neat car. Has some electrical issues . Couldn't talk him into an A-body !
I have some experience chasing elec. problems on Mopars but no expert . I replaced turnsignal switch ., which was bad. Replaced headlight switch (per ex-owner ) which I don't think was bad . Still blows the tailight fuse.  Only happens when you spin the rheostat on the headlight switch . Did that with old switch too ! Pulled dome light & drivers door jam switch& unhooked -all ok - still blows fuse .
The wiring is unmolested !
I'm leaning towards something in that circuit & dash lights ( all the same circuit).
Any ideas ? I don't have a wiring manual .
I'm pulling the dash today so should I pursue along those lines ??
It's not a grounding issue (I think ! ) cause the tailights stay lit all day long until you spin the dimming control on the headlight switch & it blows !  Help !!!!!!!!!!!!!!!! Thanks ---Mopar Tom

[Jim_Lusk]

The headlight circuit is fed by a 20A fuse to the switch and a 2A fuse to the dash lights. If you are blowing the 2A fuse check the orange wire to the shifter light in the column............

[Mopar Tom]

Jim ,I pulled the instrument fuse ,,it wasn't blowing ,,it was a 30amp,,obviously I inherited this  with the car ,,the little decal that says the fuse size is worn off from blown fuses being pried out on the instrument and tail light circuit !
Now with the inst. fuse out  the tailight fuse doesn't seem to be blowing no matter what I do . I will check that orange wire to the light in the column,,I had looked at it when replacing turn signal switch,,looked ok,,. So something on the instument circuit must be shorting fer sure ??
Should mention it leaks a little behind dash ,,wiper seals?/maybe? some fuse lugs are rusty. I guess I need to address all grnds & plugs in dash . Dash module too!!??---Thanks --Mopar Tom   

[Jim_Lusk]

Since the headlight fuse is 20S and the instrument fuse is 2A this is not logical. I'd check to make sure they didn't put a 40A fuse in for the instruments.

[Mopar Tom]

Now you lost me,,headlight fuse???/ I was hoping it had a fusible link there somewhere,,hadn't got that far,,
I'm taking your word for the instrument circuit fuse as a 2 amp & the tailight as a 20 amp. I can read the other 2 and are both 20 amp. Believe me it's logical the previous owner or buddies could have & did use a 30 amp. I tried to glean as much info from him as I could but soon realized I was on my own ! --especially after he told me they had replaced one of the front coil springs !!
Will pull the wheel next and closely inspect the orange wire for shorts,,,still don't know what to expect...even if there is a dead short in that circuit I would think it would blow a 30 amp fuse ,,or is it getting some cross voltage connection thru the rheostat control for the dash/dome dimmer control to blow the tailight fuse ?Talk to me ---------------Mopar Tom

[abqdart]

Get out your volt meter and test light. Start chasing wires. I got tired of working on my buddies 71Blazer, so I talked him into getting a painless wire kit. Put it in this weekend and man, it is sweet. It sometimes is not worth the headache to chase those 30+ year old wires around and look for shorts.

[signet]

which way are you turning the switch?
do the dash lamps come on at all?
do they dim?

[Jim_Lusk]

It looks like there are two power sources to the headlight switch. One comes from the fusable link and the other from the tail lamp fuse (20A). I'd have to pull a switch to check. The Instrument fuse is the one next to the tail fuse (on the outside).

[doug 371]

i think the cigarette lighter is on the taillight fuse also?

[Mopar Tom]

Get out your volt meter and test light. Start chasing wires. I got tired of working on my buddies 71Blazer, so I talked him into getting a painless wire kit. Put it in this weekend and man, it is sweet. It sometimes is not worth the headache to chase those 30+ year old wires around and look for shorts.

Never attack electric without my test light but volt meter would just confuse me at this point . Sorry your buddy doesn't have a Ramcharger you could help with . It's rather ludicrous to junk perfectly good 41 yr old wiring just for one (hopefully ) short . It's only 5 circuits ,,almost within the realm of my comprehension.
Mopar Tom

[Mopar Tom]

which way are you turning the switch?
do the dash lamps come on at all?
do they dim?

It didn't matter . Turn the taillights on and turn headlight switch to right to dim or left for full & full left detent for dome light,,any movement would blow fuse,,!
Saw the dashlights one time ,,didn't get far enuff to dim.  Pulled inst. fuse and cannot get tailights to blow.
Am pulling wheel today to check orange wire in column per Jim Lusk . We'll see !---Mopar Tom

[Mopar Tom]

i think the cigarette lighter is on the taillight fuse also?
[/quote
Sorry Doug ,,lighter fuse is all on it's own 20 amp circuit. You did get me lookin at it ,,sadly it seems to be the most used electric item in the car 
Mopar Tom

[Mopar Tom]

Jim !!
Success !!
Attached pic of culprit,,sorry about clarity !! It was the orange shifter indicator light . Smashed in the column
clamp. Spliced in a piece and lo & behold ,,,,,no blow fussee      Thanks fer the lead !!! I knew a 
wizard could point me in the right direction . Now on to bigger & better things ! Maybe he'll get to take his date in this car for Homecoming next week !
Who knows ,,I MIGHT get a "Thanks Dad " from Mopar Jr. -----------Mopar Tom

[Jim_Lusk]

I did EXACTLY the same thing to my GTS (yes, a column shifted GTS convertible) back in the 80s.

Now, you need to check the rating on the intrument fuse or just throw it away and install a 2A.

[Mopar Tom]

Hell with the rating ,, I got a Jim Lusk rating ! I'm gonna get me a 2 amp( if I can find one ! ) ,,got a 5 amp in her now & I ain't a feared to drop down now !!!
I think maybe those  2 feeds for the headlight switch must be for tail & other for inst. & i was getting stray voltage (maybe ?) thru the switch and the 30 ampfuse in the inst circuit was over powering the 20 amp in tail circuit blowing the weaker ? Kinda makes sense

[Jim_Lusk]

Sort of. You have a 20A in series with a 30A. The 20A will blow first in the case of a short.