74 duster headlight problem help!

[whiteduster]

been haveing a problem with my headlights thay only work on high beams not low i had some issues with the original harness so i replaced the engin and under dash harness with a good uncut non abused harness everything is fine but the headlights still only work on high beams so i replaced the head lights headlight switch and the dimmer switch still no luck i even took the instrument panel and replaced the circuit board checked the cannon plug and the headlight switch plug i even traced the wires for the dimmer switch and the head light switch still won't work on low beams what else can i do?

 

[67Dart273]

Instead of throwing parts at the problem, get your test light and meter and go to work.

This is a SIMPLE circuit.

The power SUPPLY buss TO the light switch is NOT fused. It comes from the under dash ammeter circuit from what is called the "in harness splice" directly to the headlight switch which has a breaker right in the switch. The fact that one beam works means this is OK

The OUTPUT of the switch headlight circuit feeds TO the dimmer switch. The fact that one beam works means that much is OK.

Get your test light and get down where you can probe the dimmer switch. Unbolt it if necessary. Just stick the probe in the back of the connector

Turn on the switch, ONE terminal will be hot coming from the light switch.

The other two terminals will be hot as you "switch" the dimmer, one for high, one for low.

Then the high and low feeds go out through the bulkhead (A SOURCE OF TROUBLE) and to the headlights.

First check at the dimmer for power. Next, check at the bulkhead connector for power

If you have power on the ENGINE side of the bulkhead connector on both high and low beams, then it is an issue with either bad headlights, bad lamp connectors, or possibly a grounding problem

Wiring diagrams:

http://www.mymopar.com/downloads/1974/74ValiantA.jpg

http://www.mymopar.com/downloads/1974/74ValiantB.jpg

The diagrams in this thread may also be of help

http://www.forabodiesonly.com/mopar/showthread.php?t=178025

Look at diagram A lower right hand corner, and find the "beam deflect switch" (dimmer switch)

IF the color coding is correct, "light green" is power coming TO the dimmer from the light switch

RED coming off the dimmer and going to "Y" on the bulkhead connector is your high beam feed

VIOLET off the dimmer going to "X" on the bulkhead connector is your low beam feed.

 

[RedFish]

I would remove the left bulb, get a test light, and start right there. That connector has 3 ports, high beam, low beam, and ground. If the low beam wire doesn't have power there , check for flaws back to the firewall bulkhead connector, and so on.