I'm out of ideas. The headlight fuse on my FJ-40 gets so hot I can't keep my finger on it. It's the standard 20 amp fuse. It gets hot but doesn't blow. But I don't leave it on very long either. Maybe it would blow if left on long enough. So far I've traced all wiring, added new body grounds straight to the battery, added extra hot wires from the battery to the fuse block and from the fuse block to the light switch, cleaned the light wiring block and connectors in the engine bay on the fenders, replaced the front turn signal lights, replaced the headlight switch, disconnected every running light/headlight, and checked current draw on each individually. All marker/running lights check the same @ 2.7 amps, and the headlights both check the same at 6.4 amps on high and 5.5 amps on low. Current draw total is 14.5 amps on high beam, and 12.7 amps on low beam. I thought I had found the problem with the original corroded fuse block. I replaced it and the fuses,...no change. No extra lights or anything else on that circuit.
1970 FJ-40 electrical issue
- Thread starter jim427
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pb4ugo
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Best Aftermarket headLights For Fj40
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A lot of auto manufacturers wire their headlights the same way with the same results. From the batt to the fuse blk to the switch then to the headlights. The fuse and switch and headlight wiring gets hot from all the resistance. At about $25, the Toyota kit is a no brainer, power from the batt to the lights with upgraded lenses and bulbs.
I have a 70 fj40 and I found my ignition switch was getting hot like that. Everything was rewired & good so I was at a loss as well. I put the main power on a relay instead of running it thru the ign switch and I did the same with the headlights. It should not get hot enough to effect the plastic fuse block. 14 amps at 12V with resistance caused by grounds could warm up fer sure.
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Thanks much. I ordered the kit from Toyota today. Simple and cheap fix. That fuse gets hot enough to melt the corner of the plastic cover. Just doesn't seem right. But I can't find anything else.Best Aftermarket headLights For Fj40
A lot of auto manufacturers wire their headlights the same way with the same results. From the batt to the fuse blk to the switch then to the headlights. The fuse and switch and headlight wiring gets hot from all the resistance. At about $25, the Toyota kit is a no brainer, power from the batt to the lights with upgraded lenses and bulbs.
Corrosion can crawl up a wire hidden under the insulation and still cause the circuit/wire... to run hot even tho you cleaned the connection. Relay's are a wonderful way to limit power draw threw stitches.
Living in the Past
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Typically if the fuse gets hot the issue is close by. It's resistance or over amp draw that causes the problem. Over amp heat issue would be wide spread. Loose or corroded connection would be more generalized to close where the heat is.
HI, were you able to resolve your harness issue?
My son and I "HAD" a similar issue on his 1972 FJ40 and I was able to resolve it after increasing electrical issues.
Let me know if you would like my input.
Looks like you have done all the critical / hard work.
###### Wire Harness temp measured (pre / post) 158 degrees / 107 degrees after wiring and repairs were completed.
Rod
I'll assume those temperatures are in Fahrenheit, even though it's s Toyota 
What's is your ambient temperature? You shouldn't really be getting a notable rise unless you have a corroded contact or broken wire.
With the engine stopped (steady state, no voltage fluctuations), compare the battery voltage against the voltage at the load itself.
They should be very close for things like headlights for example.
If not then you have resistance in your harness still - probably a corroded crimp terminal.
What's is your ambient temperature? You shouldn't really be getting a notable rise unless you have a corroded contact or broken wire.
With the engine stopped (steady state, no voltage fluctuations), compare the battery voltage against the voltage at the load itself.
They should be very close for things like headlights for example.
If not then you have resistance in your harness still - probably a corroded crimp terminal.
The fuse clips and spade terminals on the back corrode and cause resistance, cleaning those will help temporarily. I am going to use a little dielectric contact grease on mine to help keep them from arcing and corroding.
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