Headlight woes - '74 FJ40 -- yes, another headlight post

[GregRay]

I know there are many threads on headlight issues -- I've read them all but still can't solve my issue.

I have a '74 FJ40 (late '73 build date). Since acquiring the truck the headlights have worked about 50% of the time. When I pull the switch to the first position, the parking & tail lights always come on. When I pull the switch to the second position, the headlights come only sometimes (parking lights/tail lights stay on).

After checking connections, etc., I thought the switch was the problem. I removed, disassembled, cleaned and greased the switch and reassembled it. The headlights worked fine for about a month. However, just recently, they reverted to the former state (parking lights but no headlights). Since the OEM switch is NLA new (it's the lighted one), I looked for used or new alternatives. Based on some posts here, I was led to believe that the switch from the later trucks (post '79 and non-USA) would work, but that I would lose the ability to dim the dash lights. I picked one up (part no. 84112-60020 -- this is the one with only four metal connectors instead of the five that are in the correct part). When I plug this switch in, I get only headlights (no parking or tail lights) at both switch positions.

So, I just picked up a used '74 switch. Just tried it and unfortunately, I'm back to just parking & tail lights but no headlights. Since I can't believe two different switches each have the same problem, I have to conclude that the issue isn't the switch, but something in the wiring harness. Any suggestions where to start? All other electrics in the truck work fine.

Thanks and sorry for the long post.

 

[Colorado Boy-74-FJ40]

I would start checking the wires for shorts to ground or a high ohms reading.

 

[SouthBostonFJ40]

I have a headlight switch that you can have to see if a 3rd one gives you the same results. PM me if you want it.

 

[Rustbustr]

Sounds like a bad ground(s), mainly because you say they work 50% of the time. since park lights and tail lights work consistently, the switches are working and i would say are probably good. to check grounds use a multi meter with the 12v main battery disconnected (disconnect all batteries when checking resistances) and take resistance readings from the disconnected headlight connectors to ground on all (i believe its 3) wires. one should read low ohms and be a ground wire. two should be very high ohms, and are +12v with battery connected and headlights switched on. if more than one wire per headlight connector is low ohms probably a short, due to a melted wire or chaffing point or something, trace that one back to the root cause. best of luck!

 

[Usernametaken]

Take the power feeds straight from your headlight switch and run them through solenoids to power your headlights.
I'm not a fan of running headlights through 30 year old wiring, through your dash and out to your lights. You'll notice a massive improvement straight away.
If that doesn't fix the issue then start chasing earths.

 

[JohnnyC]

sounds like harness connector problems/corrosion...check the connectors carefully and look for green/corrosion... and if any of the wires going to the connectors are not unattached... clean up the fuse block as well while you are at it

 

[Spike Strip]

I don't know if he's still making them, but @slcfj62 makes an absolute killer upgrade replacement headlamp harness for the 40 that is a one-banana plug 'n play. Allows you to use hi-output bulbs, if you want to. You'd have to PM him to find out. I have one on my '74 and it works great, with the headlamps now nice and bright, using Osram bulbs. Comes with its own built-in relays, so it would bypass the stock one, if that's your issue.

Headlight wire harness FJ60 and FJ62

 

[Living in the Past]

I would start checking the wires for shorts to ground or a high ohms reading.

With a short it should blow the fuse, if not your looking at having a burned up wiring harness. This should be checked ASAP if that is what's happening.

sounds like harness connector problems/corrosion...check the connectors carefully and look for green/corrosion... and if any of the wires going to the connectors are not unattached... clean up the fuse block as well while you are at it

X2
I would check that connection at the switch real good. MY 68 had issues in the plug. That and problems at the fuse block.

I have one of those non lit head light switches from a non US wreck. Not sure how these work on the US imported trucks. At some point I should compared the two. My non US switch will just be used for fog lights with the lettering and symbol of the head light colored yellow as cheap way to have a close to OEM looking switch.

 

[MartynFJ4071]

Bad earth?

 

[GregRay]

sounds like harness connector problems/corrosion...check the connectors carefully and look for green/corrosion... and if any of the wires going to the connectors are not unattached... clean up the fuse block as well while you are at it

In inspecting the wires leading to the connector, I noticed that the P.O. had electrical tape around two of them. Removed the tape and two of the wires appear to be slightly "crimped" just before entering the plastic connector housing. So I'm focusing on the connector and wires right now, but still haven't solved the problem.

It's very odd that with the newer, 4-prong switch the headlights come on (but no parking or tail lights). This (in my amateur and likely wrong) opinion leads me to suspect that it is the addition of the 5th prong with the '74 switch that is causing the issue. It may be that the wire/connector to that fifth (middle) prong is damaged.

Will report back if/when I figure this out. Thanks for all the suggestions.

 

[Usernametaken]

Have you pulled your headlight switch apart and cleaned it again?
The fact this fixed your problem last time indicates to me that this is where the issue lies.

 

[GregRay]

Have you pulled your headlight switch apart and cleaned it again?
The fact this fixed your problem last time indicates to me that this is where the issue lies.

No, the fact that the lights only worked for a few weeks after cleaning indicates to me that the switch isn't the problem. Plus, I've tried two other switches since and still have the problem.

 

[Rustbustr]

have you checked the paths from the headlights to the switch with a meter? im curious what probing around the wiring would uncover. i really think this a ground issue since everything was in a working state before the headlights went haywire. you can also check the headlights with a meter and make sure they are good as well, i wouldnt rule anything out until you check it for continuity.

 

[GregRay]

have you checked the paths from the headlights to the switch with a meter? im curious what probing around the wiring would uncover. i really think this a ground issue since everything was in a working state before the headlights went haywire. you can also check the headlights with a meter and make sure they are good as well, i wouldnt rule anything out until you check it for continuity.

Headlights are fine. As indicated in one of my earlier posts, the headlights WORK with the non-USA switch (but the parking and tails lights don't work with that switch). So, something is going on in the wiring between the headlights and the connector to the switch. Headlight fuse is fine.

Car electrical issues are not my strong point, to say the least. While I'm able to do basic tests with a multimeter, I'm not really sure how to check the paths from the headlights to the switch. Where exactly should I check? And what should I check for?

Thanks.

 

[Fast Eddy]

I removed, disassembled, cleaned and greased the switch and reassembled it. The headlights worked fine for about a month.

What kind of grease? It should be electrically conductive grease.

No, the fact that the lights only worked for a few weeks after cleaning indicates to me that the switch isn't the problem. Plus, I've tried two other switches since and still have the problem.

Not unless the other two were known good switches. What was the resistance through the headlight path of each switch when in the 'on' position? You need to measure the resistance of each element of the electrical path from the battery through the bulbs to find the culprit. Take notes.

 

[Usernametaken]

I'm still betting on it being the switch.

 

[shelfboy1]

there is a dimmer switch in that circuit also they have been known to go bad