Fuse keeps blowing (1 Viewer)

[Bigstar]

Hi guys I looked on here and couldn’t fix my truck. I have a ‘71 FJ40. The fuse that controls my fuel gauge and some other things keeps blowing. Seconds after I change it. I pulled the fuse box and sanded and cleaned grounds and connections. Still doing it. PITA. Also aside from fixing the fuse issue is there an easy way to install a manual fuel gauge so I never have to deal with being stranded with a faulty fuel gauge? Asking for a friend……

 

[zerotreedelta]

That circuit is usually shared with more than gauges, and Toyota ran a fair number of constant-hot / switched-ground circuits. If any of those have trouble on that circuit, the fuse will pop immediately. I had similar with my wipers - it's shared with the washer pump, and that's a constant hot. It got unplugged and grounded out.

I'd chase down the each circuit on that fuse and see what's cranky.

 

[peesalot]

Looks like that fuse powers a few thinhgs, the back up light, maybe an issue with that switch, also the 4wd indicator light & switch are on that fuse ccording to the above schem.
If its stock wiring the other gauges should go out too, is it only the fuel gauge ?

 

[Bigstar]

Thanks guys…. no some other gauges go out too

 

[peesalot]

So have a look at the condition of the 4wd switch & indicator light, & the reverse switch & lights.

 

[charliemeyer007]

I'd bet there is a wire worn threw somewhere that is grounding out. Pull the wiring harness small sections at a time a little to shift position and perhaps isolate the dead short wire. Yep could be a socket or gauge etc. is also bad.

On my 72FJ I stuck in a rear aux tank from a Datsun B210. I added a double pole switch in the meter wire so I could read the rear aux tank. I had to buy an assortment of resistors and trial and error install them to get the fuel gauge to read from 1/2 to E on the Datsun electrics. The factory tank reads full for a long time but E is empty.

Odometer can a good fuel gauge in normal driving; low range low - then fuel consumption per hour is a better guess.

I installed a direct read oil pressure gauge (factory one was always erratic). I ran the skinny nylon oil hose inside fuel hose from the firewall to the gauge mounted on the steering column - good protection to prevent a face full of hot oil if the hose broke.

 

[45Dougal]

Get a multimeter.
Remove the fuse.
One side is the input 12v feed from the battery, the other is the output to the gauges etc.

Test resistance between the fuse output terminal and ground.
You'd normally expect at least a few ohms, but in your case you'll have close to zero (a short circuit to ground which is causing your fuse to blow).

Try then removing things which could cause it until the resistance increases to a normal (higher) value.

Unplug a cable from the front drive light.
Unplug the red blue wire from the brake switch.
Unplug the yellow feed wire from the cluster.

If you have standard wiring as per the diagram then I'd guess that a gauge moved and shorted to the case.

 

[Bigstar]

I don’t care what people say about internet nerds! You guys are alright! I followed the diagram and wires from the fuse box and you are correct….. the fuel gauge is linked to a wire that plugs into the brake master cylinder… I’m assuming for brake lights? Anyway I put new connectors on and rewired that, popped a new fuse in there and bam….. all my gauges work again! Thanks y’all

 

[45Dougal]

I don’t care what people say about internet nerds! You guys are alright! I followed the diagram and wires from the fuse box and you are correct….. the fuel gauge is linked to a wire that plugs into the brake master cylinder… I’m assuming for brake lights? Anyway I put new connectors on and rewired that, popped a new fuse in there and bam….. all my gauges work again! Thanks y’all

View attachment 3363896

Just trying to help someone out until I get enough time to go outside and fix my own truck

 

[Bigstar]

Just trying to help someone out until I get enough time to go outside and fix my own truck

Ha… it’s not easy getting out there in 100 degree weather for sure

 

[peesalot]

That is not the brake light, that IIRC is for a low fluid warning light which is not on the above schematic.

 

[Bigstar]

Great! Another thing that’s not working… my fluid was low too…. Thanks for the followup

 

[45Dougal]

That is not the brake light, that IIRC is for a low fluid warning light which is not on the above schematic.

Low fluid or low pressure?
My 77 has a pressure sensor to check you have pressure in both circuits when you brake

 

[Bigstar]

YEah curious. Where is the warning light?

 

[peesalot]

Thats a ? for others on here, I have no clue, it may not nec have a trouble light.

 

[pb4ugo]

I'm pretty sure It's the light that says "brake". It actives when the emergency brake is pulled too.

 

[Bigstar]

I know which light is the BRAKE light…. is that the same light that comes on if the fluid is low too???

 

[pb4ugo]

It does not determine if the fluid is low in the resoiviour. It's hooked up to pressure sensors at the m/c, to detect low or no pressure. If the resoiviour is empty so there's no fluid to build pressure in that brake circuit, then yes. If you blow a line, a hose, a wheel cyldr or a piston seal in the m/c the light should activate, because there's low or no pressure. It's sort of redundant cause you'll likely feel it in pedal too.

 

[pb4ugo]

I'm assuming you have a dual circuit system. I think single circuit your sol. No brakes when something pops. I think the light only activates when the emergency is pulled.

 

[45Dougal]

In my 77, the brake warning lamp serves two functions - it comes on with the parking brake obviously, but also comes on when you hit the brake but there's no pressure - not something you often see.

That's why the brake switch has 4 wires