1975 FJ40 Instrument Panel Not Working

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Groucho263

Groucho263

Joined
Jul 3, 2017
Threads
20
Messages
278
Location
Norcal
Guys,
This forum is awesome thank you in advance for the help...finally got the 40 running (after new carb, rear main seal, oil pan gasket, valve adjustment, clutch/throw out bearing work, rear output seal, fan clutch, new cooling hoses, thermostat, water heater, radiator, cooling system flush (it was bad), voltage regulator, etc.), but the instrument panel wasn't working and I couldn't tell if I had oil pressure, engine temp, fuel level or speedo.

Note: the previous voltage regulator was burnt out...and apparently had burnt quite a few wires (which I replaced after installing a new regulator).

It's a 1975 FJ40 with a 1980 2f that the PO installed. He also apparently had some interesting wiring ideas. I removed all smog/emissions wiring that I'm sure wasn't connected correctly (I'm in CA but 1975 is the magic year...so desmogged).

So, got to work on the wiring to figure out the water temp issue...ordered a new sensor, traced the wiring to connect it (it was missing)...and after install, the only thing working on the instrument cluster is the Amps. I also attached the oil pressure sensor wiring (might need a new sensor), but that didn't work either. Neither wires (at the sensor) read any voltage.

Instrument cluster connector (round connector with roughly 10 wires) has no voltage and the only voltage that shows up on the instrument cluster is the amp wiring (shows roughly 12v).

I had to re-wire light switch per the wiring guide due to burned out wires and random wiring...light switch has no voltage and none of the lights work...except the brake lights.

Stock fuse panel and all fuses except 7 are at roughly 12 volts. Fuse 7 which I think is the IG Coil reads 7.3 volts.

Motor starts and runs well (except for the exhaust leak).

I'm at a point where I need help. The circuit board on the back of the instrument cluster might have 2 burnt spots (I can't tell) and I suspect this may be the issue? I can't figure out why none of the lights work and none of the instruments work. Can I replace the circuit board...or do I need a new instrument cluster? Anybody have any ideas?

Thank you!
 
This is a " Color " coded tracer stripe wire of the locations on your 1975 cluster meter

if im correct u will 1 additional wire not shown for the emissions computer

U need to have Key ON b+ power to the blue wire with the red Tracer stripe , that's the main power input for the entire cluster , but remember key ON only


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Last edited:
Groucho263 said:
Guys,
This forum is awesome thank you in advance for the help...finally got the 40 running (after new carb, rear main seal, oil pan gasket, valve adjustment, clutch/throw out bearing work, rear output seal, fan clutch, new cooling hoses, thermostat, water heater, radiator, cooling system flush (it was bad), voltage regulator, etc.), but the instrument panel wasn't working and I couldn't tell if I had oil pressure, engine temp, fuel level or speedo.

Note: the previous voltage regulator was burnt out...and apparently had burnt quite a few wires (which I replaced after installing a new regulator).

It's a 1975 FJ40 with a 1980 2f that the PO installed. He also apparently had some interesting wiring ideas. I removed all smog/emissions wiring that I'm sure wasn't connected correctly (I'm in CA but 1975 is the magic year...so desmogged).

So, got to work on the wiring to figure out the water temp issue...ordered a new sensor, traced the wiring to connect it (it was missing)...and after install, the only thing working on the instrument cluster is the Amps. I also attached the oil pressure sensor wiring (might need a new sensor), but that didn't work either. Neither wires (at the sensor) read any voltage.

Instrument cluster connector (round connector with roughly 10 wires) has no voltage and the only voltage that shows up on the instrument cluster is the amp wiring (shows roughly 12v).

I had to re-wire light switch per the wiring guide due to burned out wires and random wiring...light switch has no voltage and none of the lights work...except the brake lights.

Stock fuse panel and all fuses except 7 are at roughly 12 volts. Fuse 7 which I think is the IG Coil reads 7.3 volts.

Motor starts and runs well (except for the exhaust leak).

I'm at a point where I need help. The circuit board on the back of the instrument cluster might have 2 burnt spots (I can't tell) and I suspect this may be the issue? I can't figure out why none of the lights work and none of the instruments work. Can I replace the circuit board...or do I need a new instrument cluster? Anybody have any ideas?

Thank you!
Click to expand...


B+ KEY should also be marked IGN. on the blue circuit board
 
RagingMatt,
Thanks for the response. I'm not quite sure I am following your response. The pictures you show are a little different than the back of my cluster. My ammeter wires go straight to the posts shown in the manual from your last post. I'll try to take pictures tomorrow in the daylight...but I have everything hooked up like it shows in Figure 11.49. My connector plug does not have ports 7 and 10 connected to anything.
 
Find the wire coming from your ignition switch that feeds 12v to the back of the board. Probably comes out of one of the fuses. You need to consult your year's wiring diagram to see the wire color code. Once you have 12 v (B+), the rest should be easy. You also need to make sure the metal case of the cluster is well grounded.
 
Groucho263 said:
RagingMatt,
Thanks for the response. I'm not quite sure I am following your response. The pictures you show are a little different than the back of my cluster. My ammeter wires go straight to the posts shown in the manual from your last post. I'll try to take pictures tomorrow in the daylight...but I have everything hooked up like it shows in Figure 11.49. My connector plug does not have ports 7 and 10 connected to anything.
Click to expand...


Note : ignore my amp meter , the example is a later cluster , But the barrell connector layout is the same color codes / location's

- also , The service manual HAYNES barrel connector #'s in the book Don;t correspond with the cast numbers on your black barrel connector , its a bit deceiving

>Like @DougAustinTx was saying , just find that Blue wire with a red stripe B+ feeding your cluster meter and the fuse that powers it and just replace the glass tube fuse for good measure

it really sounds like u have NO Key ON B+ power at your cluster meter from what u describe

also the reason u have no voltage at your oil and water sending units is because they run NEG - Ground signals NOT positive B+ ones ...
 
@DougAustinTx - The 12v (B+) wire I think is blue w/red stripe and it's connected to the barrel connector. See pictures. How do you know if the cluster is grounded properly? In the last picture, there is a connector plug with 2 wires (one white, one white w/black (which I think is the ground). I don't have another plug to connect that to and I'm not sure if that's supposed to be connected to something, etc.

RAGINGMATT - Do I need an actual wire that connects to the 12V screw on the circuit board? See pictures. I think my circuit board is fried which might be the problem (look at the burned spots near the barrel connector)? Also attached pictures at the back of the fuse panel. PO thankfully left most of the original wire colors in place.

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Thanks RAGINGMATT. Looks like I need to find a 1975 Instrument cluster...Racer65's isn't compatible with the 1975.
Any idea what the white 2 wire connector is in the last picture? Maybe emissions?
 
Quick bump to this thread...there are two wires (1 white, 1 black) connected to the speedo box on the back of the cluster. Are those needed for a de-smogged truck? Is the white wire a ground that needs to be connected. Lots of 1975 clusters have tape over those holes and appear to not have those wires...thinking they are emissions?

Second question...in the bottom (last picture), I have two white (1 white, 1 white with black stripe) that go into a female plastic connector. I don't see any wires that would connect to those. Anybody know what those are for? Emissions?
 
Not really... the WB is ground... the only W I can see (on my iPhone) on the ‘75 schematics is to the ammeter.

Schematics are HERE, by year and model.

That W is pretty yellowish (to me)... from what I can see in your picture, it doesn’t look like the wires coming out of either end of that taped harness.

The associated connector looks pretty new.

I would peel back the tape in the two wires and see if the W isn’t spliced into some other color.

I hope you’ve fixed this, above the green connector, left side of your last pic.

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Ok, I'll peel back the tape and trace the W wire...will report back. I'm wondering if it had to do with the EGR or other emission.
**Good point on fixing that spliced wire. PO did that in about 3-4 places with different wires. When you say 'fix' that...what are you saying to do (I'm learning the electrical). If I unsplice that, I'm not exactly sure how to run/connect the other wires...basically, there is 2-3 wires that combine into 1 wire. At the 1 wires termination point, there is only room for 1 wire...so I don't think running 2-3 wires into that connection is good? If I need to fix the splice so the wires aren't exposed, I can do that. Sorry for the dumb questions.
 
I can’t tell the wire colors, or the splice quality, on my iPhone.

If they are all the same color and the splice is a solid connection, you could simply tape it up.

Question: you said you’ve fixed burned wires. Were they only at the regulator, or have you had other burned wires as well.

You have your cluster out... you have your battery disconnected, right? Don’t want you to melt your harness. ;)
 
The wires in the specific splice in your post is white/black (I'm pretty sure they are grounds). They are all same color and it's a good connection.

In my first post, I tried to detail the burned wire issue...this all started because oil press, temp and fuel gauges weren't working. I just replaced the whole cooling system and wanted to make sure I wasn't over temping...or...just wanted to make sure the cooling system was working correctly and see the temperature. Which led to this whole thing...the cluster (which I did disconnect the battery) circuit board is burned out (I'm trying to get another cluster now). The wires from the lights switch are burned (not all but a couple)...and that's about it for the burned wires. Voltage Reg/lights wires mostly are the burned ones. I replaced those...lights still don't work and I am waiting on a new cluster to see if that is a cause, etc.
 
Yeah, just tape it up.

The over-rated fuses and burned wires are frightening...

If you’ve had the truck running, with no apparent issues (smoke or smell of melted insulation), you’re probably safe... just make you sure the fuses are correct.

If you haven’t had it running... be careful... check the harness, for signs of melting/damage, before you energize it.
 
I’m pretty sure all that was due to the burned out voltage reg. I had it running before I fixed that (after I started the wiring mess) and after and it runs way better now. I’m going to make sure it stays that way and when I get the cluster hopefully the lights and guages come back to life.
 
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