Guage fuse blows in drive, foot on brake (1 Viewer)

[Blue1]

Ok, I'll start with with all the basics.
94 FZJ80 - New to me 3 weeks ago. Bought in Toronto - Currently driving it back to Alberta through the US to register, travelling on 10 day in transit permit.
Guage fuse blows on first drive home, went through 3 fuses.
I picked up a 10 amp circuit breaker to use in place of the fuse to do diagnostics. The issue is intermittent and happens when shifted into drive with foot on the brake and a light rev of the engine but not everytime I do this ( does not happen when shifting through reverse or neutral on the way to drive ). I have gone through the wiring and removed any non-factory additions ( old mobile phone box, random wires soldered in and later abandoned and wrapped in electrical tape), checked where the harness passes by the EGR tube at the intake manifold, deleted trailer wiring, and generally done a thorough once over on as much of the harness as I can.

A few related notes and a bit of history - after cleaning up the non factory wiring additions I thought it was dealt with. Went for a drive and tried the cruise and it worked for a moment then the cruise light on the dash went out and couldn't be turned back on. Guage fuse still good though. Turn it off and restart it cruise light comes on and cruise works again. 2 hour drive and everything seems fine.

Set off on 3400 km trip to Alberta and everything is fine for first 6 hours or so. Driving through Chicago during rush hour and winter storm the circuit breaker trips ( no heat/guages or any of the usual items that dont work when that fuse goes). Put circuit breaker in after 15 minutes or so and everything works again. Trips five minutes later and continues to trip breaker. Pull over and unplug a few non-essentials to test ( connector in drivers footwell for power windows and another connector in that same harness, still does it )
This is when I learn thar it doesnt trip until its in drive and I give it a bit of gas.

I set out again with no guages or heat or overdrive and after about 1/2 hour I put the circuit breaker back in the guage fuse spot again and it works for a bit. I'm now learning that just before it trips the volt meter gets errattic and so does the speedo. I continue this routine for a while except after about the 4th or 5th time of this the speedo dies all together so I think this must be the problem. I get to wisconsin where I have access to a shop and hoist and check all wiring to the trans/transfer case and all looks good so I disconnect the speed sender on the transfer case. Still does it after this so I plug the speedo sender back in. I've also learned that if i plug the circuit breaker back in while driving it is good for a while ( as much as 3 hours ) so it doesnt seem to be load or heat related . Closest consistent trigger seems to be stop and go traffic.

Any thoughts or recommendations on where to look would be great. At the moment it is working and I can no longer trigger it to happen but who knows for how long. Also still no cruise control, the light on the dash comes on but with no speedo signal there is no way for the module to know speeed.

Sorry for such a long first posting ever but I wanted to include as much info as possible. Yes I have also searched and read through every thread I could find about this fuse blowing and anything that may be related to that in other circuits. That's where I got the info in the egr melting wiring and a few of the other common culprets.

Blue

 

[Tools R Us]

Fusing when throttled, a common failure is the main engine harness where it passes the EGR pipe. There was a clip that held the harness away from the pipe, likely disintegrated, allowing the harness to short on the hot pipe. Tie the harness back to the clip mount with zip-ties and see if it still does it.

 

[Blue1]

That's the first place I checked after reading many posts about that issue. No signs of damage to the factory wiring loom fabric and it does not touch the EGR tube. I did not cut back the factory covering but I did try to wigle the harness there to try and recreat the problem. Although I didn't try that while transmission in drive. Have the wires underneath ever been found to be damaged even though the outer protection is still good?

 

[BILT4ME]

There have been a few that have had melted coatings inside even though the exterior appeared OK. @Tools R Us has a ton of experience on this, so I will defer to him as well.

There is another wiring harness location up behind the glove box inside the cab. There is a small harness there that abrades on the dash frame and will short out. I'm not sure which circuit it's on, but this could be a possibility.

@Malleus is good with electrical diagrams and chasing certain circuits based on descriptions. I think he may have started to help in the other thread.

You have a very descriptive and organized methodology here, so that's good. Keep narrowing it down based on trying things.

Good Luck!

 

[Malleus]

The harness that @BILT4ME is referring to is behind the ECU, which is behind the PS knee panel. I haven't looked into it to trace the wiring inside either.

I agree your cruise control problem seems to be related to the speedo failure. The speedo signal also goes through the ECU to the combo meter. You'll need to grab a copy of the FSM/EWD to be thorough. I know you're on the road at present, so if you can narrow the serach ara, I'll post some EWD pages for you. Hopefully you get home without any more surprises.

 

[Red Merle]

Try wiggling the connectors that go through the fire wall below the brake booster. I had that fuse blowing for a while and I finally narrowed it down to the connectors where the wires went from the engine bay into the truck. Got those tight and the truck has been fine ever since. The PO had the issue, and I ended up paying someone to fix it and they were unsuccessful. I squeezed those connectors together and viola!

Electrical Gremlin Part 1 starts now...

This is where I found the fix...

10 amp gauge fuse keeps blowing

 

[Blue1]

Thanks everyone for the suggestions. Currently on the road with 1200 miles to go. Nothing like entertainment of buying a vehicle and immediately going on a 2000 mile road trip.
It’s starting to point more and more to something in the speedo circuitry. I’ve hit a couple big bumps and the speedo momentarily starts working. Another clue that may help in diagnosis is I’m 99% positive my ABS is also not working.
I am on the hunt for a FSM as I’m sure it will be invaluable. A wiring diagram would be great so I could start methodically start testing the speedometer circuits.

A bit of history about myself - I’m a licensed automotive and motorcycle mechanic and I’ve owned my share of Toyota’s but this is my first 80.

 

[Tools R Us]

...
This is when I learn thar it doesnt trip until its in drive and I give it a bit of gas.
...

The gauge fuse powers lots of stuff, so can be tough to find. This clue indicates motor torque related, don't see how motor torque movement would cause a problem under the dash? When the motor torques over the section of harness near the EGR moves, if not secured by the clip, often contacts the hot pipe. It doesn't take much contact to melt a tiny hole in the insulation. If the clip isn't in place, it doesn't take much to zip-tie the harness in place so it can't contact the pipe, good test.

 

[Malleus]

Just a thought, you might try checking the crankshaft position sensor. It's under the oil pan, near the front. Easy to get to and one more thing you can rule out.

 

[Blue1]

Well I made it all the back to Calgary and am now systematically going through each connector and tryng to look for bad connections or damaged wires. So far I haven't come accroos anything so I'm still digging. Does anyone know if the speed sensor gets power from the same source as the center dif. lock? Also trying to figure out the wire colour for power to the speed sensor. Trying to buy a FSM and wiring diagram but cant sem to find one for the 94.

 

[Tools R Us]

FSM: For Sale - 40, 50, 60, and 80 series FSM for a hell of a price.

 

[Red Merle]

Well I made it all the back to Calgary and am now systematically going through each connector and tryng to look for bad connections or damaged wires. So far I haven't come accroos anything so I'm still digging. Does anyone know if the speed sensor gets power from the same source as the center dif. lock? Also trying to figure out the wire colour for power to the speed sensor. Trying to buy a FSM and wiring diagram but cant sem to find one for the 94.

PM me if you can't find an FSM or the EWD for the '94. I have the FSM on my home computer and I think I can email it to you and I have the EWD on my work computer and can email it to you on Monday.

 

[Blue1]

Thank you ! I just downloaded it and am headed out to the shop.

 

[Red Merle]

Thank you ! I just downloaded it and am headed out to the shop.

Let me know if you need the EWD. The FSM doesn't cover everything. Good luck!

 

[Blue1]

Let me know if you need the EWD. The FSM doesn't cover everything. Good luck!

I have to say a huge thank you to Red Merle for sharing a copy of the EWD for the 94 with me. I don't think I could have found the issue as quickly as I did without it. It turned out to be the yellow wire that supplies power to both the CDL and speed sensor 1 ( supplies a signal to the speedometer) . I traced it from a connector under the dash on the right side to the EC1 connector just above the starter. There was a break in the wire after that connector. The only way to properly repair it was to pull the last section of the wiring harness and solder and heat shrink it on the bench and re-install. Thanks to everyone for all the suggestions. Couldn't have done it without this forum.

 

[Red Merle]

I have to say a huge thank you to Red Merle for sharing a copy of the EWD for the 94 with me. I don't think I could have found the issue as quickly as I did without it. It turned out to be the yellow wire that supplies power to both the CDL and speed sensor 1 ( supplies a signal to the speedometer) . I traced it from a connector under the dash on the right side to the EC1 connector just above the starter. There was a break in the wire after that connector. The only way to properly repair it was to pull the last section of the wiring harness and solder and heat shrink it on the bench and re-install. Thanks to everyone for all the suggestions. Couldn't have done it without this forum.

That's great! That's what we are here for. Glad you were able to get back in action quickly. I had a feeling it would be in that area.