So if I wanted to run a wire direct to the back of my 1974 Temp gauge, which has 3 prongs, which prong would I put the wire on?
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.
Running a direct wire to Temp Gauge
- Thread starter Chief Brody
- Start date
easiest way to make sure, is follow the printed circuit or existing wire back to the big plug that goes to the back. It will be different because none of the other gauges will share that circuit. All the others share positive and negative.
Actually it has 4 prongs...can somebody explain how it works, which prongs are for what?
Subscribed as I have the same question.
This help?
Its a dark green wire in the plug. 2and over from the left in this schematic. It hooks up where the "temp" word is in the gauge circuit board picture.
The wire is labeled 20DG-35B in the picture. I would just splice into that wire if the circuit board is good.
Its a dark green wire in the plug. 2and over from the left in this schematic. It hooks up where the "temp" word is in the gauge circuit board picture.
The wire is labeled 20DG-35B in the picture. I would just splice into that wire if the circuit board is good.
The circuit board is new...got it from LMC. Thank you for the schematic.
So, If I ran a new wire to the sending unit and tied it into that green wire at that spot in the schematic I should have a known good connection?
There is one more thing I didn't mention...the fuel gauge goes bad when the temp gauge does...is there a shared connection at all between the fuel and temp gauge on that circuit board?
If I were to run a new wire (or wires) directly to the fuel tank, where would it go? How many wires are attached to the fuel sending unit?
So, If I ran a new wire to the sending unit and tied it into that green wire at that spot in the schematic I should have a known good connection?
There is one more thing I didn't mention...the fuel gauge goes bad when the temp gauge does...is there a shared connection at all between the fuel and temp gauge on that circuit board?
If I were to run a new wire (or wires) directly to the fuel tank, where would it go? How many wires are attached to the fuel sending unit?
mrwilliamsburg33
1/2 ton status
If you have multiple gauges going out at the same time, I'd make sure the grounds are good. Not sure how yours is, but I always check grounds when things have a mind of their own...
I say either a bad ground OR a bad 12+ source as they are common for all gauges as well.
I've already checked all the chassis grounds and made new ones. Everything has a clean new ground to the battery...
battery to alternator
battery to radiator support
battery to frame
engine to firewall
battery to dash
what does the temp gauge and the fuel gauge have in common? Neither have a positive charge...right?
If one is shorting would it usually cause the other to stop working?
battery to alternator
battery to radiator support
battery to frame
engine to firewall
battery to dash
what does the temp gauge and the fuel gauge have in common? Neither have a positive charge...right?
If one is shorting would it usually cause the other to stop working?
Yep, both of them need +12 to work. And it looks like they both get it from the same wire.
When do they quit? Do you just crank it and they are dead? If so, I would suspect a problem in the ignition switch.
Next time they quit, try gently twisting the key back and forth slightly. I have seen lots of situations where the key does not return quite all the way and the gauges don't turn on.
Most trucks kill the gauges and lots of other stuff during the cranking part to protect them from voltage spikes when the starter motor is running.
So, if the key sticks slightly, stuff don't work.
When do they quit? Do you just crank it and they are dead? If so, I would suspect a problem in the ignition switch.
Next time they quit, try gently twisting the key back and forth slightly. I have seen lots of situations where the key does not return quite all the way and the gauges don't turn on.
Most trucks kill the gauges and lots of other stuff during the cranking part to protect them from voltage spikes when the starter motor is running.
So, if the key sticks slightly, stuff don't work.
I replaced the ignition switch a month ago, and I replaced the key lock cylinder switch yesterday.
Both gauges have worked before but then when I turned on the headlights they went out. So I ran a new ground direct to the dash ground point and the problem momentarily went away. It no longer caused the gauges to move when I turned on the headlights.
Then it started to do it again but they popped back to normal once I cranked the engine.
Now they are messed up all the time...cranked or not, headlights or not.
When I say "messed up" I mean that the Temp gauge is way out of range to the right and the fuels gauge is way under...it is stuck on 1/4 tank when I know for a fact that it is full because I topped it off.
Well, kinda. The schematic you have shows part of it. Look at the ign label on the temp gauge. It is the power supply for that gauge.
It hooks up to pin 39 on that side, and it looks like it goes across and powers the fuel gauge on the other side.
Then it goes down, Ts off and part goes to the fuse block.
I think that part of the fuse block is powered by the ignition switch, but the schematic gets confusing.
The main problem is that it is split up into parts. I don't have all the parts on one page.
One of these days, I need to figure out a way to print them out so I can put them together.
But, the last time I tried, it was unreadable.
Here are the rest of the pages.
Good Golly Miss Molly....The ground fault is still there with the headlight switch...I thought it was gone, but today I turned on the headlights and the temp gauge went all the way over to 3 o'clock and the gas gauge is stuck.
This is with the correct wire going to the temp sending unit.
I don't know what to do next...this thing has me beat....I could spend $120 on new gauges....something tell me that won't fix the problem.
This is with the correct wire going to the temp sending unit.
I don't know what to do next...this thing has me beat....I could spend $120 on new gauges....something tell me that won't fix the problem.
on the fuel gauge and the temp gauge....how "easy" are the needles supposed to be to turn by hand? Should there be resistance, or should they feel free floating and effortless?
Also, when I turned on the lights today the temp gauge went up and the gas gauge came down.
Also, when I turned on the lights today the temp gauge went up and the gas gauge came down.
OK, Chief, I think I have it figured out. At least partially.
Wish I was there, but I think I can explain it to you. Bear with me, its complicated.
Well, maybe not. Let me go at it this way.
There are two dashes for your truck. One with gauges and one without.
There are also two circuit boards. Again one with gauges and one without.
Somehow, I think you have a mismatch.
Look at the schematic that shows the main circuit board. (73-76 instrument) You see the second from the left hole at the bottom is numbered 35. The wire coming out of it is 20DG-35B.
That is the wire for the temp sending unit. For a truck with gauges.
Now look across to the left. That is part of the circuit board for a truck without gauges. But, the connector is cut off.
Now look at the 73-76 firewall schematic. The other half of the no gauges board is there with the connector.
Find the same wire on that connector. Its in the 6 position. Not the number 2.
The 6 position on your plug has a wire labeled 18B/W-106.
That wire winds up on the firewall schematic on the upper left side slightly below and to the left of the blower motor hooked up to something labeled hdlr. Headlight relay?? Don't know.
Its a pain in the butt, but I think your next move needs to be pulling the plug on the dash and checking the wire colors and positions against the plug diagram on the instrument schematic.
The colors should be obvious when you think about them. DG dark green, DBL dark blue, T tan, LG light green.....
I'm not sure how the harness might be wrong, and its possible the new circuit board is wrong.
But if you had the circuit board for a lights only, then you would not have anyplace to hook the gauges to.
So, the wiring seems more like the problem.
Of course, they could have just made the correct board wired wrong.
If this makes any sense, let me know if it helps.
Wish I was there, but I think I can explain it to you. Bear with me, its complicated.
Well, maybe not. Let me go at it this way.
There are two dashes for your truck. One with gauges and one without.
There are also two circuit boards. Again one with gauges and one without.
Somehow, I think you have a mismatch.
Look at the schematic that shows the main circuit board. (73-76 instrument) You see the second from the left hole at the bottom is numbered 35. The wire coming out of it is 20DG-35B.
That is the wire for the temp sending unit. For a truck with gauges.
Now look across to the left. That is part of the circuit board for a truck without gauges. But, the connector is cut off.
Now look at the 73-76 firewall schematic. The other half of the no gauges board is there with the connector.
Find the same wire on that connector. Its in the 6 position. Not the number 2.
The 6 position on your plug has a wire labeled 18B/W-106.
That wire winds up on the firewall schematic on the upper left side slightly below and to the left of the blower motor hooked up to something labeled hdlr. Headlight relay?? Don't know.
Its a pain in the butt, but I think your next move needs to be pulling the plug on the dash and checking the wire colors and positions against the plug diagram on the instrument schematic.
The colors should be obvious when you think about them. DG dark green, DBL dark blue, T tan, LG light green.....
I'm not sure how the harness might be wrong, and its possible the new circuit board is wrong.
But if you had the circuit board for a lights only, then you would not have anyplace to hook the gauges to.
So, the wiring seems more like the problem.
Of course, they could have just made the correct board wired wrong.
If this makes any sense, let me know if it helps.
There is one thing I haven't done yet...that's to clip the wire going to the fuel sending unit...is it possible that a shorted out fuel sending wire would cause this?
I could clip it where it comes out of the firewall harness and see if that fixes it.
another thing I thought about was the hi-beam switch in the floor....
I could clip it where it comes out of the firewall harness and see if that fixes it.
another thing I thought about was the hi-beam switch in the floor....
near Huntsville...north alabama
Have you disconnected the plug from the printed circuit board yet and inspected the circuit board termination where the plug makes contact? I had a vehicle once that gave me some fits and it turned out that as I had plugged the connector into the cluster one or more of the terminations from the circuit board got twisted up and where causing a short (it's been years ago and I can't remember exactly what was going on but it's definately something to check if you haven't already).
