Testing a headlight switch with a multimeter

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iw378

iw378

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I am in the process of rewiring my car. Is there a way to function test the headlight switch by hooking up the test leads to the switch, running the switch through the motions and make sure the the wiring is in the right spot ?
Any insight appreciated..
 
Not sure what you are getting at. If you are trying to check out the wiring "in place," not so much. If you are only attempting to figure the function of the switch, yes

Look at the wiring diagram.

You have TWO power sources going IN.

One powers ONLY the headlights, so those two contacts are only made in "full on" headlights, and make no contact with any other terminal

The second power source goes to the switch from your tail fuse

This powers tail, park, and the dash lamp dimmer. So with the switch in "park" all of those terminals will show continuity with each other.

The switch contacts should be marked on the switch. If not, refer to the pictorial in the wiring diagram

===================================================

Using resistance to check an in-place harness is somewhat more difficult because of feedback etc in some circuits. A far better way is to hook everything up "safely" for testing, except the battery ground. Then hook a LARGE 12V lamp in series with the battery NEG terminal to ground. Use a headlamp, if you have nothing else, a stop / tail lamp with the two filaments in parallel. This will protect everything against shorts while testing.
 
You can test the switch out of the car per this info, and use it to know when/what should be connected.

B1 (Battery 1) should connect to H (Headlights) when the switch is pulled all the way out. There is an internal circuit breaker between these 2 contacts; those can fail open occasionally.

B2 (Battery 2) should connect to R (Rear? Red? the tailights anyway) and to P (front Parking lights) when the knob is pulled to either the 1st or second positions.

B2 also feeds the dimmer rheostat in the switch; the resistance from B2 to I (Instrument lights) will vary from maybe 15-20 ohms down to near 0 ohms as you rotate the knob.

D (Dome) should connect to the switch's metal case/body when the knob is turned all the way to where it 'clicks' to turn on the dome light
 
The switch is out of the car and yes thats what I was looking for to find out
"what goes where"
Thanks
 
nm9stheham said:
You can test the switch out of the car per this info, and use it to know when/what should be connected.

B1 (Battery 1) should connect to H (Headlights) when the switch is pulled all the way out. There is an internal circuit breaker between these 2 contacts; those can fail open occasionally.

B2 (Battery 2) should connect to R (Rear? Red? the tailights anyway) and to P (front Parking lights) when the knob is pulled to either the 1st or second positions.

B2 also feeds the dimmer rheostat in the switch; the resistance from B2 to I (Instrument lights) will vary from maybe 15-20 ohms down to near 0 ohms as you rotate the knob.

D (Dome) should connect to the switch's metal case/body when the knob is turned all the way to where it 'clicks' to turn on the dome light
Click to expand...


Just resolved hours of troubleshooting and found a bad dimmer using this. Thank you!!!
 
69dartV02 said:
Just resolved hours of troubleshooting and found a bad dimmer using this. Thank you!!!
Click to expand...

I ran across a bad dimmer on the Wife's 72 Dart that was keeping the dash lights from working at all, so I jumpered from the back of the fuse box tail light fuse terminal to the dash lights wire.
Only difference it makes is that the dash lights wont dim any longer, and if I ever replace the switch I can just take the jumper off.
 
Wow...someone used the 'search' function LOL

And IIRC, some of the older switches are a bit different.... my '62's front parking lights (the B2 to P connection) are only on when the switch is pulled out to the 1st position; they go off when the headlights are on in the 2nd position. Not sure if you can buy this older version anymore; I rebuilt my old switch to keep the original functionality.
 
Actually Ma did not change the switch when they changed from the "park" function to "on with headlights" Same switch. All they did was to move the P wire on the switch over and tie it with the tail terminal. And of course "we" can do the same thing!!!
 
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