Ultimate Headlight Mod Harness - Intermittent

Hey guys, this issue relates to the ultimate headlight mod that is well-loved on this forum. I’ve had the harness installed for just shy of a year and in the last months for so I’ve been getting intermittent headlight function. I’ve isolated the issue to the harness because if I plug the original harness back in, my headlights work without a problem - this has been my workaround for when this happens.

from what I can tell, the two days this has happened have been very wet, and very windy. The first time I unplugged the connection from the harness that supplies power to the headlights and some water came out from the plug, headlights started working after that.

today was not the same case, checked all the connections, they seemed good - wouldn’t work no matter what. Unplugged the harness and plugged in the OEM plug, do my 45 minute commute, get to work, plug in the harness and it’s working again.

My immediate idea is to get some bulb grease and put it on the prongs and see if that helps? Not sure if that’s a good approach, was hoping to be blessed with some of the wisdom you fine folks always offer me.

Thanks.

 

As you say, I would pack the connectors with dielectric grease (it will be cheaper to get a tube of that as opposed to the little packs of bulb grease, and you'll have it on hand for the next time you touch any of the other electrical connectors in the engine bay or under the truck). While doing so, look for splits or poor connections in the rest of the harness - it's possible a bad crimp or damage may be allowing water to wick into the connectors from the wire side.

If you do find problems with the harness itself, I would contaAsct the manufacturer - it would surprise me very much if he didn't stand behind the product.

 

My first move would be contacting the supplier and asking for diagnostic guidance and suggestions for repair.

In addition to those 2 things you *could* get a new harness offered. And they may want to see the old harness to look for defects.

A phone call is free, and much easier to have an iterative conversation than an email string.

@crashnburn80 any suggestions?

 

I'm going to guess that the water that drained out of the connection probably corroded the contacts over time. Applying any kind of grease now will not solve that problem. Once corrosion starts, you need new connections because the protective plating is now gone. I'd contact your harness supplier. I'd also protect that connection from water intrusion in the future. (Yes, dielectric grease works much better on uncorroded connections.)

 

I'll get in touch with the harness manufacturer and go from there.

It seems a decent amount of the corrosion exists on the OEM side of the harness within the female connector. The male side (aftermarket harness) shows no visible signs of corrosion. Logically I would say if the harness can be ruled out as the problem, I would move on to replacing the female connector on the OEM harness. Looking down in it I just see corrosion all over, I can't visibly see where contact would be made sufficiently.

Followup question: Does Toyota sell new connectors ready to be spliced, or do I have to go aftermarket?

Thanks everyone, I appreciate the guidance. If anyone else has anything to say I would appreciate the input.

 

@daveeasa might be able to help you with a connector.

 

For my Tundra specifically and possibly for my 2nd gen, I plan to cut and crimp OEM sealed connectors. I haven't done that yet though b/c of priorities.

What would I do?

Either

• Cut and splice together the OEM wiring and the aftermarket harness making sure to do one wire at a time. Use heat shrink butt connectors and some outer heat shrink over all 3 wires to make it look clean. The harness is now non-removable but the connections should be good for the life of the truck. This is the easy option.
• Cut and crimp a sealed connector onto the OEM side and a corresponding alternate gender sealed connector on the harness side, making sure to note which wire goes where.

This change only needs to be done on one side and it is possible to simultaneously make a pigtail from the severed H4 OEM female (or a replacement) to the sealed connector so that you could subsequently run without the harness in the future (if the truck were to be sold).
I am OCD so I would do both sides to match and I might pre-crimp pigtails for going back to "stock" but I also might wait and do that only if needed.

On my 2016 I actually cut off the OEM H9 and H11 connectors and re-crimped to a sealed 4 way connector for high and low beams, a very similar move, though the H9 and H11 male & female connections are at least water-resistent (just the males are not the same quality level as the Yazaki / Sumitomo stuff.)

Wire gauge does not matter for the harness as this is purely a trigger, but if you ran without the harness you might prefer a beefier wire on the pigtail.

These are my favorite option for premade female pigtails:
https://ceautoelectricsupply.com/product/h4-9003-headlight-pigtails/

I would pick 14 over 12 in this context since these would be purely for stock wattage off the OEM harness rather than building your own relay. You could use this for option 1 if you want or go sealed and use these only as your back to stock option. They also sell raw terminals and connectors but crimping these things to tiny wire is truly not fun. And why do tons of work only to have the same water intrusion potential down the road?

For a 3 position sealed connector, I might go with the triangle style (it's used in 3rd gen Tacoma brake and I don't think it's present on a 2015)
https://www.corsa-technic.com/item.php?item_id=665

These are your turn/drl/park signal connectors (same story for me on my tundra and 2G tacoma)
https://www.corsa-technic.com/item.php?item_id=666

Also this option:
https://www.corsa-technic.com/item.php?item_id=808

On the female side (truck side) you want to pick terminals and seals for 20 gauge wire size (in corsa's numbering scheme these are the 1's)
On the male side (harness / pigtail side) you want to match the wire gauge you're using. Note 14 gauge is the biggest you can stuff into these sealed connectors so that's SL4 (or SL3 for Yazaki) and PIN3 on the terminal.

I can recommend a basic crimper if you need one, I like the green weatherpack non-ratcheting for pure value but I own a dozen or so and I mix and match when building.

Hopefully some of this was helpful?

 

And to be super clear, I see no good reason to retain this connector when using a harness and no real downside to having one extra connection + a pigtail to H4 for "going back to stock". Some people might disagree and talk about resistive loss over two connections vs 1. I would say the benefits of a sealed connector outweigh any possible concerns with 20 gauge wire and H4 unsealed connectors and anyone interested in headlight performance should be using a harness anyway. I would definitely consider hacking off the H4's on both sides and replacing with sealed connectors (which can then be capped to prevent water intrusion on the unused passenger side) as an upgrade. Unfortunately there's no way around H4's at the bulb but you can use higher quality than OEM on those.

 

I appreciate the write-up, I've re-read it multiple times to make sure I fully understood what you were conveying and it was all 100% helpful information to consider.

The two options you presented are both intriguing, I'm going to ponder what I should do should I need to. I genuinely like the idea of directly splicing OEM to aftermarket harness as there is no real disadvantage to this other than not being able to immediately return it to OEM. The quality of the kit in my opinion is high quality based off of the write-up Crashnburn did as well as from the retailer website - as well as my own opinion but my opinion doesn't mean much in a situation like this.

On another note, I spoke with Headlightservices which is the company who produced my harness, I'm essentially paraphrasing here but he stated something along the lines of the connectors themselves don't really fail, of which I believe this would be true in my case as I peered at the female and male connections from the aftermarket connector and saw zero corrosion (upon a quick visual inspection). He said the only part of the system that can fail, albeit rarely, are the relays - he is sending me two new relays at no charge to help assist with my issue, something that I wasn't expecting. I don't really think it's the relays as I could here them clicking when trying to turn on the headlights earlier with no dice, but I've been wrong on things before, so I'm willing to try it.

This thread has been useful and I appreciate all of the informative responses from everyone. I feel as if I have a clear direction on where to go from here, but further responses are appreciated.

 

Stellar customer service from Headlight Services - as usual!

 

Yeah, Mike is cool and knows his stuff. I have two of his harnesses myself, just need to get them installed someday.

It could be a loose connection at the relay or a faulty relay, so good of him to rule that out. You can test that with a multimeter on pins 86 and 85 of the relay once you have the trouble. If you get +12v between the two and no headlight output then that says the relay isn’t doing it’s job. You’ll first have to identify which is high beam and which is low beam. Easiest way is to pull one and see, assuming lights are working when you pull.

a multimeter will help troubleshoot, they aren’t expensive.

 

If the relays are clicking that means they are getting power. From there they would be pulling power directly from the battery to power the headlights with nothing else in between save the battery connections and the plugs at the bulbs.

Assuming you’ve got good connections at the battery and bulbs, seems like 1 of 2 things:
1. There is insufficient voltage delivered from the OEM connector to hold the relays closed due to corrosion. If this is the case the relays may click but not hold. This may cause a relay to flutter.
2. The relay is defective. Just because a relay clicks doesn’t mean it holds or makes contact to complete the connection.

Replacing the relays will confirm or eliminate option 2.

 

On several occasions I've had relays fail due to water ingress. In MOST of those cases, the relay would click but had no continuity across terminals 30 and 87. Just something to consider.

 

I’m going to pick up a multimeter so I can test for the next time this occurs, but I think ultimately I’m going to move my relays somewhere else under the hood, I have them mounted on the side of the engine bay near the battery and I think water might be getting to them. I may design and print a water tight box to put over the relays as an additional layer of protection on top of that.

 

If you want to be verrrrry fancy, there should be a couple unused relay slots on your factory fusebox.

 

It’s possible to use sealed relays too. But I haven’t found any skirted which have dual 87 outputs. That style is well suited to this application.

I might hack mine up and just convert to 4 sealed relays myself. Or a GEP and micro relays but they max out at 20 amps so I’d still be using 4 of them for that. At least I could use an internal bus bar for power and ground.

A 3D printed mounting box would be a nice quick solution. @switch, I could send you my harnesses if you are game to build a prototype. I have one power switched and one ground switched, new in packaging (so no dirt). It’s a good plan.

 

My new M.O. is to silicone the back side of the relay connector to prevent water from getting in where the wires pass through the connector. Then pack the hell out of the connector with dielectric grease. If the relay isn't sealed, I do my best to seal that as well. I've never had a relay fail due to water since doing this.

As mentioned placement is also important. Keep them mounted in as dry of a location as possible. I personally prefer relays without dual 87 terminals for the OP's reason. If the relay fails you've lost all your headlights. Using multiples reduces the chance of losing all your headlights at once.