Running Lights - beyond the fuse.....

[CHS78FJ40]

Running lights went out yesterday - no big deal, right..... grab a new fuse and swap it out. Wrong - fuse was blown - 15A glass fuse - replaced it no problem. Still no lights. (Headlights and brake lights still work - just no front or rear running lights)
New owner of my '78 FJ40 - bought from a great friend three weeks ago, so still learning the drill, but have no clue where to go from here.
Any thoughts would be greatly appreciated.

 

[John McVicker]

Did the replacement fuse blow also? If yes, you've likely got a bare wire touching metal somewhere.

 

[CHS78FJ40]

Did the replacement fuse blow also? If yes, you've likely got a bare wire touching metal somewhere.

Surprisingly it did not - sorry I failed to mention that.
Wasn't sure if maybe there would be another fuse in-line that I was missing.

 

[John McVicker]

If it did not blow, it's most likely the ground or maybe the bulb itself is not seated properly.

Turn the lights on & move the bulbs a bit. If that's not it, rig up a wire with alligator clips on each end for a temporary ground test. Prob one of these 2 will tell you what you need to know.

EDIT: good idea to actually verify the replacement fuse is good. And to clean the slot where the fuse goes.

 

[Solace in Solitude]

Running lights out in front, back or both?

Are the tail lights and license plate light working?

‘78 running lights (front and back) are powered by the same G(reen) wire as the tail lights and license plate light.

Here’s the ‘78 wiring diagram

http://www.globalsoftware-inc.com/c...ics/FJ40/1978FJ40/1978fj40_wiring_diagram.pdf

Do as John suggests and see where that takes you.

 

[CHS78FJ40]

Running lights out in front, back or both?

Are the tail lights and license plate light working?

‘78 running lights (front and back) are powered by the same G(reen) wire as the tail lights and license plate light.

Here’s the ‘78 wiring diagram

http://www.globalsoftware-inc.com/c...ics/FJ40/1978FJ40/1978fj40_wiring_diagram.pdf

Do as John suggests and see where that takes you.

Thank you all for the suggestions.
All running lights are out - tried wiggling bulbs to no avail. Tail and license out also. Fuse still good - tried another fuse and cleaned contacts on fuse block.
Now I’m thoroughly confused.

 

[3_puppies]

do you have a test light? check for power on both sides of the fuse, not just on the fuse but the holder.
if all lights are out, next is a switch issue. as each light should have it's own ground.

 

[Solace in Solitude]

Do as @3_puppies suggested, it’s all about proper maintenance.

If the fuse is good AND the fuse contacts are clean AND the contacts have power, on both side of the fuse,

​

clean the connections on all your main ground straps. Make sure they all connect to shiny metal.

All these light fixtures ground to the body. It could be as simple as poor main grounds.
​

If you KNOW you have power on the contacts, on both sides of the fuse AND your main grounds are clean,

Drop your light switch and clean the contacts on it.

Check for power on the Green-Red wire, at the switch.

Turn the lights on and check for power in the Green wire, at the switch.

If they both have power AND
​

The lights still don’t work, come back.

The “15A Tail” light circuit is shown here:

 

[vt0u812]

I’m chasing the same issue/characteristics as you CHS78FJ40. I’m curious if you’ve also lost your dimmer abilities on your instrument panel (via twisting the light switch knob w/ your lights on). I’m trying to figure out if we have the same problem.
Tomorrow i’m Pulling my switch and trying Solace in Solitude’s suggestion.

 

[RIBob]

I am having the same issue with my 79 FJ40. Shorted the circuit with an under dash bulb that made contact with the metal housing. It blew the 15A “tail” fuse. Running lights and dash lights out as expected.

Replaced 15A fuse and confirmed power on both sides of the new fuse… did not fix the problem.

Any thoughts appreciated.

 

[charliemeyer007]

Did you check the other fuses - maybe it was changed to a different circuit. You might look around in the wiring for an added in line fuse. Good time to clean/inspect all the plugs connectors.

 

[RIBob]

Thanks for the post. The precipitating even was inadvertent grounding of the positive contact on the under dash lamp as the LED bulb was wider than the the incandescent bulb. My bad for not noticing that.

To answer your question, all other fuses are good as is the one I just replaced (power on both sides of the fuse. Everything on that circuit is out - running lights, license lights and dash lights. All other electrical is working correctly.

The fuse that blew turned out to be a 20a and it calls for a 15a (which is what I put back in). (Never thought to check that someone would put in the incorrect amperage fuse)

There is no way every ground on this circuit went down at the time of the short, so either it caused a positive wire to “melt” because it was a 20a fuse rather than a 15a, or the short caused the “Light” switch to fry just the part of the switch (Headlights still come on when the switch is fully pulled.

 

[charliemeyer007]

40 year old wiring pushed 25% harder than it was designed for - yep could have easily fried something. Those opened crimp connectors can easily corrode, that corrosion can also crawl under the insulation anywhere there is an opening. Corrosion is resistance and that means more heat.

Volt ohm meter and start checking everything. Maybe one of those clamp on signal checking units.

Back in the 90's I blew up my wiring diagram to like 16" x 24" and had it laminated. On the back I did tune up specs and part numbers - should have added other stuff like torque #'s. Very handy for old eyes - glad I made several copies.

 

[RIBob]

Problem solved.
1. I took out and bench tested the light switch. Works properly.
2. Pulled the neg cable on the battery and unscrewed the fuse block to better expose the wires.
3. Started testing continuity from the back of the fuse block to the light switch connector. All good
*4. Checked continuity between the fuse prongs and that is where the fault was. *

Lesson learned: continuity between the ends of a fuse (which was the first thing I checked after replacing the blown fuse) is not the same as checking continuity between the prongs that hold the fuse in place. I do recall reading another thread that emphasized cleaning up the contact points. Had I done that I would have saved a lot of head scratching. Next time.

Thanks to those who responded so quick. On to the leaking rear transfer case output seal/shaft.

 

[John McVicker]

Dirty fuse…exact same thing happened to me 2 days ago…dirty fuse. OHM’d the fuse in question by touching the exposed metal..all good, pulled the fuse…looked fine, OHM’d the very bottom of the prongs…all good. But still no workie.

Then I noticed the prongs themselves were not at all clean. Wire brushed the prongs & inserted the same fuse & all good.

This was on my auxiliary fuse box with added relays to my starter. Make sure the contact part of your fuse is actually clean.

 

[pb4ugo]

Periodically when trail riding I'd pull the lights and nuthing. I'd reach down to the fuse box and move the fuse back and forth in the fuse holders. If that didn't work, I'd pull the light switch back and forth to clean it's contacts.