headlamp switch connections

Valcuda · Post by **Valcuda** » Wed Nov 09, 16 4:57 pm

Here's a problem for you electricians!

I'm trying to work out what the headlamp switch connections are on a spare switch I have before I go to the hassle of removing my own to hunt for an electrical fault (lack of panel lights) on my 69 Barracuda.

I've worked out that B1 is from the battery and H goes to the headlamps. B2 is from the tail lamp fuse and R goes to the tail/parking lamps. D is for the dome lamp and P is not used. The slightly cranked tag at the knob end (the manual calls it I but it's unmarked on my spare switch) comes from the wiper on the rheostat disc behind the knob and goes to the instrument panel fuse. But where is the rheostat powered from? Is it (internally) from B1 or B2? Perhaps my spare switch is broken but I don't get any electrical connection (using a circuit tester) between I and either B1 or B2 in any switch position. The wiring diagram in the 1969 manual doesn't show the rheostat

Here's the layout of the tags in the attached photo:

----------- B2--------- D
--------P---------- H-----
----B1------R-----------I

I wonder if somebody out there with a spare unfaulty switch could do a quick test and tell me, or perhaps somebody knows anyway, having been through this process.

Thanks guys

ANTON · Post by **ANTON** » Thu Nov 10, 16 7:05 am

Most problems with dash lights are the rotating resistor coil not getting good connection. the one in your picture has all the green corrosion on it and that resistor is what controls the brightness of the dash lights. the are two connection to that resistor and if you bypass it the dash lights will be full brightness all the time.

GJUK · Post by **GJUK** » Thu Nov 10, 16 10:45 am

I took mine apart, knowing that you can buy new ones from I think it was rock auto for about Â£15. They are not as good as the original ones but never the less, they are around.

you can drill out the rivets and it all falls apart.

There are some metal slider contacts inside which (on mine) were burnt and needed a clean up.

I stuck it back together using a strong adhesive and its fine now.

I tested the circuit by bridging the wires on the wiring loom to show it was the switch at fault.

J

Dave999 · Post by **Dave999** » Thu Nov 10, 16 11:44 am

I don't think the rheostat is powered

I think its is earthed to the metal bracket internally in the switch .

the dome light is live and switches on when you connect it to earth/body

via
a door press switch popping out when the door opens and completing a circuit to earth

or

you completeing the circuit to earth by twisting the rheostat to the point where none of the coils are "in circuit" and the little bendy connector on the switch hits the stud at the end of the coils in the rheostat. the end of least resistance

I think "I" powers up the circuit to the interior lights and dash light

the dash light brightness is controlled by the resistance in the earth that you adjust with the rheostat

and the interior dome light only gets in on the action when that tiny bendy connector eventually hits the end rivet on the rheostat.

just mulling it over. don't have a switch to hand

dave

GJUK · Post by **GJUK** » Thu Nov 10, 16 12:03 pm

they are earthed yes, that is a good point.

octanejunkie · Post by **octanejunkie** » Thu Nov 10, 16 2:40 pm

ANTON wrote:Most problems with dash lights are the rotating resistor coil not getting good connection. the one in your picture has all the green corrosion on it and that resistor is what controls the brightness of the dash lights. the are two connection to that resistor and if you bypass it the dash lights will be full brightness all the time.

I've fixed many classic car dash lights "by magic", cleaning up this connection. Rotate the knob round vigorously for a few moments, and normal service is often resumed!