Headlight Switch Information and Repairs

Squarebirds  (58-60)

Draft #1

July 10, 2008

 

Contents:

1)      Function

2)      Access/Removal

3)      Wiring details

4)      Repair of instrument light power loss

 

 

 

1.     Function

The switch is always live – it does not run off of the Key!

 

The Headlight switch does the following

a)      takes a 12V supply from the battery (not switched – always On)

b)     provides power source for the Key

c)      provides power to headlights and taillights (and license plate light)

d)     provides power to parking lights

e)      provides power to the dome light

f)       provides variable power to the instrument lights

g)      provides power to the brake lights at all times

 

 

through the following actions

 

            the knob is pulled all the way out for headlights

            the knob is pulled part way out for parking lights

            the knob is rotated counterclockwise all the way for the dome light

            either door is open for the dome light to come on

            the knob is partly rotated, dimming the instrument lights

 

2.     Access  and/or removal

 

a)      disconnect the + post on the battery!!!!!  (there is a live wire to the switch and you also may scare the hell out of yourself by leaning on the horn)

b)      remove the bezel and Fuel/Temp gauge  (3 small Phillips head screws, 4 wires – make note of which wires go where). Now you can look in the hole in the dash and have a good view of the Headlight Switch.

c)      push the knob on the Headlight Switch all the way in.

d)     Press the spring loaded button on the Switch (see the upper blue arrow in the photo pointing to a round, silver thing) and pull the Knob and Shaft out. I needed a flat blade screwdriver to do it. This is a key step,

e)      Remove the bezel by unscrewing it

f)       You should now see the entire switch and be able to drop it down under the dash if you wish

 

 

3.     Wiring Information

 

 

Heavy yellow wire held on by a nut is the 12V source from the battery

 

In Cap letters the others are labeled in functional ways:

 

B  - to battery  (hot!)  via Starter Relay   #10 Yellow, held on with nut. Also has a wire to the Ignition Key on this post.

 

D     - to dome light – 3 green wires together  (1 for each door, one direct from switch)

            has the 7.5 A glass fuse in line.

 

A    -  to  brakelights via hydraulic switch on master cylinder  #18 Green

 

I       - to instruments            #18 Blue with red band

 

H      - to headlights via foot switch.  #16 Red with yellow band

 

P       - to parking lights  #18  Black/yellow band

 

R     -   to tail lights and license plate light. #18 Black

 

XX  -  two posts on underside of switch, not marked Anyone know???

 

There is a 7.5 Amp glass fuse on the end for the dome light as well.

 

 

4. Repair of the Instrument Light function

 

Every old car I have ever seen has had no instrument lights, unless it has undergone a serious overhaul. Every one. The problem is always the same. But some background first.

 

Someone decided that you should be able to vary the voltage to your dashboard lights. So they designed a rheostat  (variable resistor) for the light switch. I have found this identical on Fords, Corvettes, Studebakers and Chryslers.

 

So they have what amounts to a long, thin wire in a toroidal configuration around the switch.  The farther along you tap into it for your instrument lights, the more the voltage drop and the dimmer the lights. Tap into it at the beginning and you get all 12 volts.

 

Fine but the thin wire gets brittle with age and breaks.  No more instrument lights.

 

Problem Identification:  first you need to make sure the switch is your problem. Get a jumper wire  (a foot or less, with a probe at each end or an alligator clip. Turn the headlights on  (you will need to put the shaft and knob back in).  No instrument lights.

Look at the photo again and see the lower blue arrow in the photo pointing to a silver post. This is the post the instrument lights get power from (or used to ).

 

Now run the jumper from the silver post marked I to the next post, marked R.  If you have instrument lights now, you know the switch was your problem.  If not, somehow you blew out half a dozen or so #57 bulbs all at once and/or have a tougher problem.

 

Solution #1:  buy a new switch.  About $70 for TBirds.  Now you can dim your lights again.

 

Solution #2: bypass the rheostat and have 12V to the instrument lights all the time (when the headlights are On) and save the $70.

 

Solution #2 has the down side that you can no longer dim your instrument lights.  I have yet to meet anyone who cared to do this. If you do, see Solution #1. Personally I wish mine were a little brighter!!

 

So how do you bypass this rheostat?? Easy!!! 

 

1)      Disconnect the wire from the silver post marked “I”.  That wire goes to your instrument lights

2)      Splice it into the wire immediately adjacent to it on the copper post marked “R”. 

 

There are a number of ways to splice it in, and heat shrink tubing or liquid rubber or something reliable to protect the new joint is needed. If you solder, this is a good time.  The connector is a female standard spade connector available everywhere, should you chop off the old ones.

In the photo above, the sort of ugly red thing is where I made a Y adapter to the R post and used red Liquid Rubber to coat it. Both original spade connectors are still there. A cleaner version would be to cut both off and solder both to a new female spade connector but I like to leave wiring harnesses unmolested if possible.

 

That’s it!! You have bypassed the rheostat and your dash lights will be the full 12v whenever the headlights are on because post R  is for the tail lights. and is thus only live when the lights are On.