Low beam head lights not working

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Apr 8, 2019
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The low beam heads lights decided not to work any more. They work in high beam but not low, which is confusing cause that means there is current going to the bulbs and the bulbs are functional. I googled this problem to see if any one has ran into this before and there is not much out there. Some have mentioned the relay under the dash behind the fuse box. I checked with Toyota that part is no longer being made and they could not tell me any information on the relay. I have no issue replacing it a 4 prong relay is $5 but I don't know the voltage or amp it takes. I did inspect the relay it self and it look good clean and the slapstick shrink wrap is still around it. I need some help on this I don't know what to do.

Right now i'm driving around with the high beams on all time it i'm going to unplug the inner bulbs so the cops wont give me a ticket for high beam driving.

1978 toyoyta hilux 20R
 

roscoFJ73

 
 
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This is the 70 series forum , not the 1970s. But Im sure those relays can be sourcd easily. Electrical parts usually have the voltage and amp specs printed on them.
Try this part number 85916-35010 , they are used on other toyotas as well and there seems to be few around if you google it.
 
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You should determine if there is voltage to the low beams before assuming its a bad relay; could be a bad ground to the relay.
Disconnect the connector off the back of the light and see if there is voltage going to the headlights low beam elements.
There are three slots on the connector. Determine which one is ground by measuring resistance from the lead to ground. Just measure ground to ground, power to low beam and power to high beam.
 
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I used a light bulb not a voltage meter to determine if there was power going to them when they were working. At first the driver side went out, that's when I checked for voltage and there was very little power going to the driver side bulb. Then a week later they both stopped working. I checked all wires and connections from the bulbs to wire harness nothing seemed out of the ordinary and no corrosion or issue.

The only ground I see is under the battery box and some around the radiator. Are there any other I should look for?
 
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My recommendations were for general troubleshooting; I am not familiar with the wiring for a 1978 Toyota Hilux.
 

pappy

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They work in high beam but not low, which is confusing cause that means there is current going to the bulbs and the bulbs are functional.
The only ground I see is under the battery box and some around the radiator. Are there any other I should look for?
First, I think you are on the right track. Toyota wires the lights different than most companies. There is positive power to the negative terminal on the bulb. The high and low beam terminals on the bulb ground through the switch. It could be the switch. It could also be the low beam ground coming from the switch.

My suspicion is it won't be the relay. There is only one positive wire and if the relay is charging the high beam, it's also charging the low beam.
 

roscoFJ73

 
 
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I also dont think it will be a relay. Are you sure the low beam filament is working? Ist not uncommon for one to blow out then have the other go out in sympathy. It happened twice on my landcruisers.
 
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Thanks guys for the replies. I will test out the bulbs and the switch this weekend I order 2 bulbs should be here on Friday. I can pull out the switch and refurbish the connections see if that works out better.
 

KLF

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This happened to Roger Brown's (is he still around?) old 4Runner, he had a write-up on his site somewhere. It was the Hi-Lo switch in the column, the contacts were worn out.

Maybe somebody can find it on his site, I'm in a hurry to leave for work right now. Good luck.
 

yotadude520

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This happened to Roger Brown's (is he still around?) old 4Runner, he had a write-up on his site somewhere. It was the Hi-Lo switch in the column, the contacts were worn out.

Maybe somebody can find it on his site, I'm in a hurry to leave for work right now. Good luck.
I think this is what Ken was referencing:

Brighter Head Lights
 

CreeperSleeper

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This happened to Roger Brown's (is he still around?) old 4Runner, he had a write-up on his site somewhere. It was the Hi-Lo switch in the column, the contacts were worn out.

Maybe somebody can find it on his site, I'm in a hurry to leave for work right now. Good luck.
I think this is what Ken was referencing:

Brighter Head Lights
Actually, I think it is the switch repair, not the brighter headlights.

However, usually the combo switch makes you loose high beams usually.
 
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