License plate light and 15 amp fuse

Joined
Apr 21, 2022
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Arizona
Hello all,

I am new to Fj ownership and I much appreciate this forum. I have been looking for answers to my problem but I'm not finding a solution per se. I have a 76 FJ40 with which seems to be the original electrical harness but with some fixups here and there. Last week I took off my top and ambulance doors. The liscence plate lights didn't have a disconnect so I cut them and attached female bullet connectors on the positive wires leading from the body (see pic).

After removing the door and adding the bullet connectors I re-attached the wires just to verify that they work. Mind you, the door was disconnected from the body and just being held for a test. The lights didn't work so I was confused and assumed I must have pulled too hard on the wire, disconnecting something below. I inspected the wiring and nothing was pulled loose. According to the schematics (see picture) it says the wires go to the lights then to a ground. This led me to believe that I should remove the female bullet connectors and just attach the wire to the body???? When I did connect them to the body the front side marker and front parking lights started to work again.

That's one thing I hadn't mentioned. The 15 amp fuse kept blowing and the front parking lights and front side marker lights would come on but very dimly and then the fuse would blow. After having connected the liscence plate wires to the body, they light up like they should have, leading me to believe that I was doing the right thing.

After I thought I had it figured out, I went to adjust the brightness and then they all went back to dim and the 15amp fuse blew again.

I removed the light control switch and cleaned the contacts on the inside in hopes that would fix it. It did not.

In addition to all of this, I can not get the Headlights to work. The weird thing is that I tested the connector that goes to the light control switch to verify that the lights were receiving 12volts, which they were.

So now I don't know what to do. Get a new light control switch? Do I need to track down a short circuit? Any help would be appreciated.

20220420_161430.jpg


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Joined
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Messages
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Location
Arizona
Lights didn’t work because door was removed from the body. They ground through the body.
I did cut off the female connectors to the liscence plate lights and attached the bare wires to the body. I am still not getting anything when turning on the lights and it just blows the circuit. Could it be the switch?
 

Cromagnon

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It sounds like the 15A fuse is saving your 40 from burning to the ground. If you are taking both of the wires from the license plate light and grounding them you are creating the short that is causing the over current protection device (fuse) to open, protecting your wiring and vehicle from combusting. You should have a load (light bulb) between the green wires and ground. The original ground came through the body and doors as mentioned in post #3. When you removed the doors from the body you removed the ground to the license plate light.
 
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Messages
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Arizona
It sounds like the 15A fuse is saving your 40 from burning to the ground. If you are taking both of the wires from the license plate light and grounding them you are creating the short that is causing the over current protection device (fuse) to open, protecting your wiring and vehicle from combusting. You should have a load (light bulb) between the green wires and ground. The original ground came through the body and doors as mentioned in post #3. When you removed the doors from the body you removed the ground to the license plate light.
This is probably the answer. I will report back when I have tested this out. Thanks
 
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So I figured out the problem. In the process of removing the top I must have dislodged some wires. One of the wires for the lights in the back made contact with the exhaust and melted and was shorting out the system. So problem solved.

On a related note. The Headlights turn on now but they are very dim and the high beams do not work at all. Any sugestions??

I switched over to LED headlights and I am wondering if I need to add resistor, but I haven't seen anyone mention a need for that on their installs.
 

Cromagnon

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You mentioned that you "switched over to LED headlights" yet you do not give any specifications for them and you are wondering if you "need to add a resistor." Are you using headlights that require a voltage different from 12VDC? If they require something less, then you would need a resistor. Do you have voltage on the two power leads going to the headlights? What is the reading? How many amperes are you measuring on the leads with the lights illuminated? Did you clean the grounds when you installed the new headlights?
 
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Messages
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Location
Arizona
You mentioned that you "switched over to LED headlights" yet you do not give any specifications for them and you are wondering if you "need to add a resistor." Are you using headlights that require a voltage different from 12VDC? If they require something less, then you would need a resistor. Do you have voltage on the two power leads going to the headlights? What is the reading? How many amperes are you measuring on the leads with the lights illuminated? Did you clean the grounds when you installed the new headlights?
I purchase these ones from cruiser corps.


Leads are showing 24.7 mv just off of battery power on low and 38mv on high.

With engine running its showing 35.5 mv on low and 44.8mv on high

It seems the voltage es must be too low...?

I am abseloutly terrible at electrical and also new to old cars so any help would be great.

Headlights say they are rated for input voltage of 9-32V DC
 
Joined
Apr 21, 2022
Messages
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I purchase these ones from cruiser corps.


Leads are showing 24.7 mv just off of battery power on low and 38mv on high.

With engine running its showing 35.5 mv on low and 44.8mv on high

It seems the voltage es must be too low...?

I am abseloutly terrible at electrical and also new to old cars so any help would be great.

Headlights say they are rated for input voltage of 9-32V DC
Just cleaned the ground and only got an extra 2 Milliamp increase
 

Cromagnon

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Messages
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In Post #1 your schematic shows all of the points that need to be verified to find the issue. Start at the Headlight Fuse (20A). Then use the half split method to determine where the problem lies. That means find a place half way between the fuse and the headlight and take a measurement. If there is the proper voltage then go towards the headlight. if not towards the fuse. When you check the fuse DO NOT use the visual method, use a multimeter. Also clean the fuse holder contacts until they are bright and shiny.
 
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Messages
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In Post #1 your schematic shows all of the points that need to be verified to find the issue. Start at the Headlight Fuse (20A). Then use the half split method to determine where the problem lies. That means find a place half way between the fuse and the headlight and take a measurement. If there is the proper voltage then go towards the headlight. if not towards the fuse. When you check the fuse DO NOT use the visual method, use a multimeter. Also clean the fuse holder contacts until they are bright and shiny.
A followup for you help. There was a major drop of voltage at the fuses. Come to find out that the PO or PPO had for some odd reason installed a ground wire from the headlight fuse to the frame for a reason I can only scratch my head at. Anyway. The Headlights are up and working great and I appreciate all of you help. Electrical work is the worst and makes me slightly hate working on an old car. I'll have to do some research on replacing the wiring harness because there is so much old stuff going to nowhere that frustrates my inner perfectionist.
 
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Good luck finding another harness. @Coolerman doesn't offer them anymore. I'm working on building my own, as soon as I find wires equivalent to the 40 (or 80) Sumitomo wires, which are proving ridiculously hard to locate. I know I can get his sprial traced wires, but that's not what I'm looking for, and his specs aren't exactly Sumitomo's. Probably good enough, but I'd rather have their JIS automotive AEX wires.
 
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Good luck finding another harness. @Coolerman doesn't offer them anymore. I'm working on building my own, as soon as I find wires equivalent to the 40 (or 80) Sumitomo wires, which are proving ridiculously hard to locate. I know I can get his sprial traced wires, but that's not what I'm looking for, and his specs aren't exactly Sumitomo's. Probably good enough, but I'd rather have their JIS automotive AEX wires.
Please let me know if you do make another harness. I would be interested in duplicating or buying one from you. Best of luck.
 

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