map light behavior and proper wiring?

[miketyler]

My maplight has been intermittent and I want to fix is but it is turning out to be one of those things that you think you can fix quick and it ends up taking all afternoon.

I know the maplight is switched but does the maplight come on with the domelight? I only ask because I am getting 12V to both legs of the lamp when the switch is on. I have checked the wiring diagram and it looks like it receives 12V all the time from the red mold connector. The ground is supplied by the switch which for some reason is getting power thru it. The switch has a ground strap and it is making good contact to ground. According to the diagram the switch is connected correctly and has a single yellow bullet lead which plugs into a single receptacle with two yellow wires (no tracers)

I have to study this closer but I think that yellow lead should be grounded. Has anyone seen this type of behavior?

[MEK-Dangerfield]

Mike,

 The map light does NOT come on with the dome light. The +12 volts is always there. It's the ground side that is "switched". Maybe your switch is acting up?


  Mike

[miketyler]

no, switch is good. I did have to shoot some contact cleaner in it and work it but is now showing <1.0 ohms resistance when closed. No, my problem seems to be that power is coming into the switch and it should be ground.

I guess I could just disconnect the incoming lead to the switch and ground it but I would sure like to know where its getting power from.

[GoodysGotaCuda]

There is how much resistance in that switch? You should do a voltage drop test on that switch. Close the switch, then put one lead on the wire that goes to the bulb, and the other to the dash ground. Post what the meter says.

[Robb]

do you mean when the dome light comes on from opening the door ?

[miketyler]

its about ~.2 ohms from post to post when the switch is in the closed position and is infinite in the open position. I believe the switch is fine. The fact that power is coming into it I believe is the problem.

Dome light comes on with the doors and goes out as it should

[miketyler]

yes, just tested and if I connect only the lead going to the light to the switch and ground the other leg of the switch the light operates as it should. The switch should be connected to a ground source but instead it's getting power from somewhere.

[MEK-Dangerfield]

Mike,

  Maybe you misunderstood me. In these cars, there is ALWAYS power on the map light switch. It's the ground side the is either "connected" or not.  It's completely different from the modern way of thinking.


  Mike

[Bullitt-]

not sure of you year but I don't think this changes much. In my '73 Service Manual & in this '70 diagram on line http://www.mymopar.com/downloads/1970/70BarracudaB.JPG the map light is part of the door switched circuit. In the manual there is a section on accessories that gets more in depth showing a time delay is involved & indeed one leg of the switch does plug into a red power source.

[Bullitt-]

from the '73 manual

[miketyler]

Yup - thats very similar to the 72 diagram, also illustrates the switch is supplying the ground. Thanks for that. My problem is that the bulb is getting power from the red mold always-on source AND from the switch.

After looking at it more closely, this may have something to do with my overhead console addition. It appears the map light works correctly only if the dome light is switched on at the panel dimmer switch. To further complicate things when this same switch is turned on, it cancels the door switched activation. This feature might be handy when you are at the drive-in and getting out of the car and you dont want to expose your half-naked girlfriend to the other patrons.   

This is reminding me of a Stooges episode where they had done some electrical and plumbing work and a light bulb filled with water when they turned it on. 
I can probably live with this but I am puzzled. I didn't splice anything. The overhead console and time delay harness was all original and plugged right in. It should function exactly the same as a Gran Coupe or RT with an overhead console. Thanks for all the responses thus far.

[MEK-Dangerfield]

Mike,

  I forgot you had the overhead console thing going on here too. I really have NO input as to how that works with the map light. Sorry.   


  Mike

[ShelbyDogg]

Mike, I haven't been under my dash in a while but when my dome light comes on, my MAP light comes on too.  When My dome light is off (doors closed) the map light will come on if I pull the switch towards me, turning it on.  I don't store my car here so I can't look at the wiring.  My light also acts funny and dim sometimes when I turn it on manually. I think it is getting a dirty ground through the switch ground.
Rob

[Chryco Psycho]

I agree Map light wil come on with dome light but cam be grounded through the switch
somehow the switch must be plugged in wrong feeding power to both sids of the switch

[71 DEPUTY]

1- red wire is batt 12 volts-power all time.

2- switch in one position- door open- light comes on- yellow wire grounds thur door switch

3-switch in other position-- light is on- lamp is grounded via internal ground from switch to case.

factory manual doesn't show this " extra " ground by a symbol- to them it's a given known thing.