OEM Engine bay wiring harness ground points

[Yaris_80]

I have a very dim passenger side headlamp, and from what i have gathered its most likely a bad earth ground or wiring issue. Hoping its a oem ground point. If someone has a diagram or knows where all of them are I'd appreciate it.

- All fuses are good.
- Headlamp bulbs are brand new and have tried two dif sets.

[Amdkt7]

measure the voltage on both sides of the bulb, connecting the meter to ground. Should be 12.8-13.8 volts on one side and nearly zero on the other. Assuming you can get a meter on the bulb with the lights turned on. That will tell weather it is a ground or power issue.

[Yaris_80]

Just multi-metered the three prong bulb while connected to the socket and the lights on, all three prongs were in the 0.01-0.03

[Amdkt7]

ok, did you connect the one meter lead to ground (negative), and then measure the voltage on the terminals?
The meter should be set to measure DC volts. Usually shown as a V with a straight line above it. If you measured .01 volts on all three terminals then the light should not be on at all. Or you did not find a valid ground for the meter.

[Yaris_80]

I grounded it to the valve cover, Not the plastic one.

Black lead went to the valve cover and red went to the prongs, and now the light isnt on at all.

I swapped the bulb from the pass side over to the driver's side and the bulb worked fine.

[Amdkt7]

check this thread:

http://www.toyotanation.com/forum/102-1st-2nd-generation-1983-1986-1987-1991/277434-one-dim-headlight-one-bright-headlight.html

[Amdkt7]

One guy found his connector at the back of the bulb to be messed up:

"OK. I finally managed to get the plastic connector to come off the back of the bulb. It was all bubbled and brittle as if it had maybe been arcing and melted. I didn't have a new one so just tried to clean up the contacts a bit with a very thin file and some WD40. Working ok now but the plastic is very 'crumbly' so will have to get one from the scrappy and re-wire it.
Thanks for your help folks. "

Try wiggling wires and the connector and see if the lights come on. It is probably at the connector for the bulb.

[Yaris_80]

ok, Dont entirely get the coupler deal. The headlamp harness end up in the fuse box...So is he saying the plugs that go into the fuse box.

Side note- Headlamp harness is brand new from toyota.
Plug in are secure and completely in the fuse box connectors.

[Amdkt7]

Also, trace the ground wire back and see if it is bolted to the frame at some point. Take the bolt out and clean all the connections, bolt back tight. I'd add some dialectic grease it that turns out to be the problem.

[Yaris_80]

Wiggled headlamp socket, wiggled the bulb, fuse box connections, wiggled known grounds.. nothing. Put it back on the driver side. immediate success. Going outside to trace ground wire to passenger side bulb socket.

[YarisSedan]

http://www.ebay.com/itm/H4-9003-CERAMIC-YARIS-WIRE-HEADLIGHT-HARNESS-SOCKETs-bi-xenon-female-PIGTAIL-HID-/290820628157?pt=Motors_Car_Truck_Parts_Accessories&hash=item43b6429ebd&vxp=mtr

here you go 6 bucks for 2 not a bad deal maybe even cheaper/better than junker

[Amdkt7]

so, you replaced the wiring from the bulb to the fuse box and is still does not work?

[Amdkt7]

There is a relay that controls the lights too. I don't have a wiring diagram, so I don't know if one relay controls both left and right. If there is a separate path for left and right (dual circuits in the relay) then it could still be the relay. Perhaps there are two relays, one left and one right. I don't know.

If you grounded the meter right (and it sounds like you did) then the problem will be on the positive side of the circuit, and not the ground side. You can verify ground by (with power off) by measuring from the ground terminal of the lamp connector to the neg side of the battery, or perhaps on the engine block. Should be less then 2-3 ohms, hopefully more like .2 ohms.

[Yaris_80]

Yes, The headlamp harness is brand new.

I checked on the ground going from the pass side to the fuse box, No ground on the solid black wire, It goes from the bulb to the fuse box and plugs into the 1st row/3rd slot in that pigtail. only ground on the whole harness is a white wire with a black stripe going the length of the wire and that bolts up on the drivers side frame rail.

[Yaris_80]

Relay was bad, Kudos Amdkt7 =] =] =]

[Amdkt7]

I'm glad you got it fixed!