I put in a headlight harness to power my H4 bulbs. Hooked it up just as instructed when I tried it out I had marker lights only, no low beams or high beams.

Here's the harness I used: http://www.wildhorses4x4.com/product...Wiring_Harness

It gets switched power from the pass side factory headlight plug, so with that still plugged into the new harness, I swapped plugs on the driver side from the new harness to the old plug. When I did that, both driver side and pass side lights came on.

I've been working on multiple projects today, so I decided to just put everything back to the way it was and pull out the new harness for now. I did, but now I have the same issue - marker lights only - no high beams or low beams.

Please help!!! This is my daily driver - I need headlights. The fuse box is (labeled) so confusing, I cannot even tell which fuse is for the headlights.

 

Update: Thanks to 4crawler's website I realized that the headlight fuses were under the hood and I found that both the right and left were blown.

I'll replace them in the morning but am still perplexed why the new harness isn't working.

 

If both headlights were working before the new harness and now both fuses are blown, then I would guess you have a faulty harness. Try replacing the fuses, and try installing the harness and check the fuses after each step of installation to see what makes the fuses blow

 

Thanks. I'm not going to be able to dig into this again for a couple of days. What's really got me puzzled is (pre-fuse blowing) why it took the driver side headlight being plugged back into the stock plug to make the new harness work on the passenger side (one light powered by the new harness, other powered by stock wiring -- the only config that allowed the lights to work).

Can anyone help me understand why this happened?

 

Sounds to me like some where with the new harness you lost your ground.

Since the ground is through the head light plug it might just be a poor connection.

try cleaning both the parts were they plug in.

I have had plugs that looked fine to the eye cause all sorts of problems.

 

Come to think of it, you may be on to something. My PIAA fog light relay was mounted close by. I mounted the new harness' ground wire ring terminal on top of the zinc plated bracket (sharing the existing screw) coming off the relay instead of under it against the body.

Perhaps that's the issue. I'll know shortly.

 

Is the new harnes running as a switched ground circuit? I believe your truck is a switched negative. So 4 crawlers site shows how to switch the upgrade harness to work with that.

 

^^^^ This.

 

Are switched negative and switched ground the same thing? Not making any assumptions at this point

 

Yes and no. Switched ground typically refers to switched negative, but switched ground can also be used to describe switched power where ground is positive (uncommon).

The harness you bought is designed for a switched power circuit, so you need to convert it to switched ground:

http://www.4crawler.com/4x4/CheapTri...s.shtml#SPtoSG

 

The harness was intended for a 66-77 early Ford Bronco. I'll have to research more

 

The more I read, the more confused I get. Is my 86 4runner switched power or switched ground?

 

Sorry. Found my answer - I have switched ground. Trying to research on my phone has made it more challenging.

 

Just in case you missed it.

In case you don't know where to look: http://www.4crawler.com/4x4/CheapTri...s.shtml#SPtoSG

 

Thanks. It looks like I can move some wires around and add a resistor in to make the harness work. However, I'm not sure what to use to contain the new resistor to protect it and keep it dry. Any suggestions?

 

I believe the resister is just there to prevent the lows from staying on with the highs. With my homemade wiring harness I don't have the resister and my lows stay on with the highs. I kind of like it that way. And In my case the high beam indicator does work. It's just a tad dim because some of it's current is being used to trip the low beam lights. Which is why you need the resister.

 

In this case, switched ground and switched negative mean the same thing, so it was probably confusing for the guy. The harness appears to be for a switched power setup, so yes he needs to convert it.

 

To clarify, yes, my new harness is switched power - so I need to reconfigure it.

 

Quoting from 4crawler.com: "But before converting the harness, you may actually want to temporarily plug the switched power harness into your headlights to both verify that high and low beams work normally (they should) and if your high beam indicator lights or not. At least this way you'll know that everything with the harness and your existing headlight system is working before you decide to convert the harness, if needed, to switched ground operation."

Note the section I underlined, it seems that the wiring harness you have may be faulty as your low and high beams did not work normally. My 0.02.....

 

It could be, but it's just wires and relays. So if I move everything around as he says, I should address any faults as well.

Thanks everyone for all of the replies!!!!