headlight problem 78bj40 (1 Viewer)

[Greg_B]

Fuses good? Same problem if you switch bulb sides?

You should not get the same voltages on the left and right side headlight pins. Read the above info in post #2 thoroughly for pin readings with headlights off, on low, on high. Left side is the 12V side. Right side is the 24V side. If you are not getting 24V on the correct pins on the right side but are showing 12V neutral...that would be your problem (24V wires not working).

The headlight dimmer relay has a 24V lead into it, as well as the 12V center tap. Check that the 24V side is working. If it is supplying 24V to the dimmer and no 24V coming out to the two lines that need it (high and low when selected) then sounds like the dimmer relay is not working on the 24V side.

hth's
gb

EDIT. Just saw your update. Yup, sounds like you have it. If you are showing 24v into the dimmer relay and nothing out...sounds like the relay is not switching the 24v inside as needed.

 

[YSG2017]

Thx for your help Greg. My 24v out of fuse and into dimmer is ok.
I took apart the dimmer relay and it looks ok also.
How am I even getting 12v to the passenger headlight at all when the switch turned on?
It has to be the harness on both hb and lb leads coming out of the relay to the passenger headlight right?
Strange since the drivers side light functions properly.
My centertap 12v appears fine all the way through the circuit also.
Yup, also flipped and tested bulbs.
Somewhere between the dimmer relay and the headlight I am losing that 24v and only getting 12 there.

 

[YSG2017]

Fixed it. What a bugger. It was a harness ground hidden way under the dash that had been compromised by both corrosion and paint. It prevented the 24v part of the circuit from working with the 12v centertap neutralization when under current draw. Totally crazy electrical engineering Toyota in this stupid setup. Why not just use 24v headlights instead?!