Newbie electric question on 1970 B for map light

I'm a new member and owner of a great little '70B - nicely renovated this summer. First off, the hazzard light connection looks to have been repaired by the PO. The attached photo is the back side of the lower console, the brown wire must have been bad and they had run the yellow wire up to the harness and attached to the hazzard switch (far left). These work fine. However, the map light is dead and I'd like to get it working. The purple wires running from the door switch are also not connected (you can also see this in the photo on the right side). How do I trouble shoot this problem? Should I splice into the new yellow wire that was installed and attempt to connect this to the map light? Where would I make the connection? Where would the purple wire connect to if I want the door switch to also trigger the map light?

Best Regards,

Jim

First, download the correct wiring diagram for your car and print it in color. Some have printed them at 11 X 17 and then had them laminated.
http://www.advanceautowire.com/schematics

Brown wires are unfused and always hot; that is not the correct wire for your map light. Note that purple wire is hot from the fuse panel to the light and the purple/white wire goes from the light to the door switches. The switches establish ground and complete the circuit. Get a test light and see if the purple wire has voltage and test the ground side of the circuit.

Thanks Keith... the purple is hot, but it's not connected to anything (top right corner of the photo). The only wires on the switch are a purple/red and green/red - neither is hot.

The door switch should have only one wire on it, purple/white, and it is the circuit ground.

Looking at the schematic, you should have 3 wires on the light; hot - purple, door switch - purple/white, and ground (manual on) - black.

The map light on a 70 only works if the headlights are on. Thats why you have a red/grn wire on the switch. It is not connected to the door switch in any way. The power comes in when the lights are on and the switch sends it to the light which is grounded.

Gary,

I've followed this thread as I too have a 70 B (GT). I agree that the map light only works when the headlights are on. But what do the door switches do?

I have a GT and I would have thought that the door switches activate the dome light but the wiring diagram shows the switches going to the map light.

I can understand the logic of the map light working when the headlights are on (headlights on means it's dark out therefore only activate map light when it's dark, you don't need it if it's light out). But who would open the door(s) with the lights on?!

As this entire door switch lighting circuit seems to be disconected in my car anyway I'm going to wire the doors switches to turn on the dome light but the whole map light / door switch / dome light thing as wired by the factory has me confused ......

Got it on the map light...thanks!!!! Regarding the door switch - I guess this was probably connected to some other interior light that was never re-installed????

The map light gets it's power from a single purple wire that should probably come from the unused purple connector I see floating in your picture. The map light switch takes a ground and passes it through to the map light when activated causing the light to come on. The door switches are also connected to the same ground system, after the map light switch so that any time a door is opened, ,a ground is provided via the door switch and the map light comes on.

For those of you who need to have your headlights on to get the map light to work, someone has probably connected the cigarette lighter recepticle light power wire (red/white) which is connected to the other instrument lights, to the map light and hence the reason you need headlights on to have it work.

The power for the map light comes off of the same fuse as the horn system, so if the horn works, your fuse is good. It's a single uninterupted wire(purple) from the fuse up to the map light , so if you have no power at the purple connection, you either have a bad connector, ie very corroded, or a broken wire that you're going to have to go hunting for.

I hope this helps a bit.

The map light circuit on a 1970 was wired from the factory to operate with the headlight or parking lights on. The door switches did operate the map light on later models. In the attached wiring diagram the courtesy/map light is on the left side about 1/3 way up. The door switches on a 70 GT provide a ground for the dome light located just in front of the hatch.
I don't know of a courtesy lamp on a 70 roadster.

http://www.advanceautowire.com/mgb.pdf


Go to page 5..

Gary,

You're right with that particular diagram, but the way the problem was described, it sounded as though the map/courtesy light was one in the same which made me look at diagram 6 for the 70/71. This diagram has the circuit as I have described it.


JIm, verify what set up you have and if I've misunderstood the problem, then Gary has this one nailed.

Earl,

Gary (and Tim) have it right - thanks everyone..! My correct wiring is diagram 5, not 6. I found I have plenty of juice through the red/green with the headlights on. I think the problem is a faulty maplight switch. I can jiggle it with the headlights on and make the map light flicker on. The door switch does puzzle me. I don't have a purple/white, just a solid purple and purple/green coming from the door. It would be nice to be able to hook this into the map light as a courtesy light.

Jim

Ok, Ok, so I was using the wrong wiring diagram. I was using page 9 / dia 9 as it shows the side marker lights when page 5 / dia 5 does not. (Confusing?)

There's four diagrams that can cover a 1970 B so I had a 1 in 4 chance of being right....

Thanks to all. Great post! This cleared up a bunch of questions that I had but now I don't have to post!

Great call Michael...! My buzzer must not be working...thought this was a light switch.