VDO Temp Gauge Wiring - Defender Source
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  #1  
Old August 22nd, 2013, 05:53 PM
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VDO Temp Gauge Wiring

I'm swapping out my factory temp gauge for a VDO unit. Anybody know off hand which wire on the back of the factory unit is the sender?
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Old August 22nd, 2013, 05:54 PM
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Photo of the back of the gauge:
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  #3  
Old August 22nd, 2013, 06:12 PM
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Old August 22nd, 2013, 06:24 PM
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Thanks bro!

I also saw first hand how important a good ground is for the instruments. The engine hasn't run for a week (It's stone cold) and the oil temp started rising when I turned on the ignition. I have yet to run a new ground for any of the gauges.
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Old August 22nd, 2013, 10:20 PM
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Quote:
Originally Posted by javelinadave View Post
Thanks bro!

I also saw first hand how important a good ground is for the instruments. The engine hasn't run for a week (It's stone cold) and the oil temp started rising when I turned on the ignition. I have yet to run a new ground for any of the gauges.
Electrical load (especially headlights and fans) used to significantly affect my VDO temperature gauge. I ended up running a second ground to the engine, replacing the ground from the battery, and took apart, cleaned, and re-assembled the ground headers. The temperature gauge now only seems to be affected by the cooling fans, and then it's only a jump of 5 degrees.
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Old August 22nd, 2013, 10:30 PM
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The wiring harnesses on these leave a lot to be desired...I replaced the one my 110 and we are finishing up another...It's money well spent just to replace it. It solved all my ground issues, along with new chassis grounds. If you ever get down to Tucson, let me know...buy ya beer...

also are you replacing the sender unit?
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Old August 22nd, 2013, 10:43 PM
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New gauge, sending unit and I'm going to run a new ground for all the gauges to the firewall.
I make it to Tucson from time to time, I'll get hold of you when I do.
Thanks!
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Old August 23rd, 2013, 08:57 AM
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These gauges work by having a reference 12 v to compare to the voltage coming from the sender and a ground. This allows the to give a reliable reading even as the system voltage changes.

The bottom line though you have to have a good ground for this to work. On the gauges that's the black wire.
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  #9  
Old August 23rd, 2013, 10:22 AM
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My v8 gauge seemed to do just fine with its own ground to the firewall. I did try first without its own ground and it was not working correct. I wanted to know how serious they were on having its own ground. Turns out pretty serious. I

like this thread about the tdi gauge and using a dedicated larger gauge wire:
http://www.defendersource.com/forum/...t=Housing+temp
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Old August 23rd, 2013, 11:08 AM
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This may help.

Quote:
Originally Posted by michael67 View Post
Electrical load (especially headlights and fans) used to significantly affect my VDO temperature gauge.
Had the exact same issue, so to add to the good advice from Michael.
To get an accurate reading ran a wire from the (+) battery cable off the hot side of the starter to a relay that is switched by the ignition key. Then ran a separate ground wire from the bulkhead itself. Next installed the sending unit that matched the new VDO gauge and the readings were accurate. Finally used a infrared temp gun to verify accuracy.

With this setup when the key is switched on the relay jumps (+) power from the battery over to the (+) side of the gauge. The ground is not shared with any other device and the wire from the sender goes straight from the sending unit to the gauge.

Some of the Smiths and Jaeger gauges used a current stabilizer that put out a constant amount of current, usually 10V, so if you by chance had this on the old gauge make sure you don't incorporate it into your VDO gauge wiring.

Hope this helps.
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  #11  
Old August 23rd, 2013, 03:18 PM
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Super easy swap. Other than a screw driver all that is needed are about a foot of wir, a few new terminals, a crimper and wire strippers.
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  #12  
Old September 5th, 2017, 04:00 PM
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Quote:
Originally Posted by michael67 View Post
Electrical load (especially headlights and fans) used to significantly affect my VDO temperature gauge. I ended up running a second ground to the engine, replacing the ground from the battery, and took apart, cleaned, and re-assembled the ground headers. The temperature gauge now only seems to be affected by the cooling fans, and then it's only a jump of 5 degrees.
I am going through this now. When my electric fan kicks on the temp gauge increases by about 20 degree's, then drops once the fan turns off. Right now water temp gauge has a seperate ground to the inner dash spot on the LH side. I think I am going to try running the water temp gauge ground right to the battery or this extra fuse box in the battery compartment. Headlights don't have an impact but they are LED so not much of a power draw.

------ Follow up post added September 5th, 2017 02:05 PM ------

Quote:
Originally Posted by rdavisinva View Post
Had the exact same issue, so to add to the good advice from Michael.
To get an accurate reading ran a wire from the (+) battery cable off the hot side of the starter to a relay that is switched by the ignition key. Then ran a separate ground wire from the bulkhead itself. Next installed the sending unit that matched the new VDO gauge and the readings were accurate. Finally used a infrared temp gun to verify accuracy.

With this setup when the key is switched on the relay jumps (+) power from the battery over to the (+) side of the gauge. The ground is not shared with any other device and the wire from the sender goes straight from the sending unit to the gauge.

Some of the Smiths and Jaeger gauges used a current stabilizer that put out a constant amount of current, usually 10V, so if you by chance had this on the old gauge make sure you don't incorporate it into your VDO gauge wiring.

Hope this helps.
Ugh that sounds overkill. Did you try just running ground straight from gauge to negative battery?
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  #13  
Old September 5th, 2017, 05:00 PM
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You want the gauge grounded to the engine. I ground the gauges to a separate lug on the bulkhead behind the dash and a ground wire from the bulkhead to the engine. Any voltage between the sensor's ground (the engine) and the gauge results in an incorrect reading.
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Old September 5th, 2017, 05:22 PM
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Quote:
Originally Posted by Red90 View Post
You want the gauge grounded to the engine. I ground the gauges to a separate lug on the bulkhead behind the dash and a ground wire from the bulkhead to the engine. Any voltage between the sensor's ground (the engine) and the gauge results in an incorrect reading.
That makes a lot of sense. Thank you.

I'll get a little BlueSea bus bar and mount it on the bulkhead that gets fed from the engine block.
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Old September 5th, 2017, 06:09 PM
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Quote:
Originally Posted by AdamSanta85 View Post
Ugh that sounds overkill. Did you try just running ground straight from gauge to negative battery?
The overkill you refer to I used follows the manufactures instructions.
Share any wire and gauge reading will be inaccurate.

The very worst thing you can do is run a separate wire from the battery to anything other than the frame.
If you use battery ground to anything other than the frame all the vehicle ground could try and use the directly wired device, in this case a VDO gauge.
And if it does decide to use the gauge as the vehicle ground source the gauge will melt and catch fire instantly.
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Old September 5th, 2017, 06:47 PM
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Quote:
Originally Posted by rdavisinva View Post
The overkill you refer to I used follows the manufactures instructions.
Share any wire and gauge reading will be inaccurate.

The very worst thing you can do is run a separate wire from the battery to anything other than the frame.
If you use battery ground to anything other than the frame all the vehicle ground could try and use the directly wired device, in this case a VDO gauge.
And if it does decide to use the gauge as the vehicle ground source the gauge will melt and catch fire instantly.
Why would all the vehicle grounds run through a small gauge wire to the sender?

voltage always follows the path of least resistance, you would have to have all other grounds fail to have everything route back to the temp sender on the engine block...

I just routed all my grounds to terminal blocks (LED indicators/brake lights) and blue sea bus bars

2 of these behind the front headlights, 1 behind the gauges on the bulkhead:


1 of these in the engine bay:


2 of these in the back:


Tied into one of these in the battery box:


The only thing grounded to the frame is the engine and starter, everything else goes back to the battery. No possibility of back feed since everything is headed back to common using 10 gauge Ancor wire and the only significant load (starter) has its own ground
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Old September 5th, 2017, 06:52 PM
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Quote:
Originally Posted by NPT90 View Post
Why would all the vehicle grounds run through a small gauge wire to the sender?

voltage always follows the path of least resistance, you would have to have all other grounds fail to have everything route back to the temp sender on the engine block...

I just routed all my grounds to terminal blocks (LED indicators/brake lights) and blue sea bus bars

2 of these behind the front headlights, 1 behind the gauges on the bulkhead:

1 of these in the engine bay:
of these in the back:


Tied into one of these in the battery box:


The only thing grounded to the frame is the engine and starter, everything else goes back to the battery. No possibility of back feed since everything is headed back to common using 10 gauge Ancor wire and the only significant load (starter) has its own ground
Looks Really Good!
All that will work fine provided you don't hook a direct wire to the negative (-) battery post to supply ground and it looks like you didn't make that mistake.

Quote:
Originally Posted by NPT90 View Post
Why would all the vehicle grounds run through a small gauge wire to the sender?
A separate wire from the (-) battery post to anything other than the frame can be used as a ground source when the connection from the battery to the frame is lost.
We had a TD5 in the shop that the owner wired both the radio (+) and (-) directly to the battery.
When he lost frame ground, lightening shot out of the radio just before it caught on fire and melted during start-up.
The same thing could happen if electrons decided to go through the gauge and force a ground.
If you want to experiment, disconnect the ground strap from the battery to the frame to simulate loosing your ground through corrosion.
Then run a separate small wire from the (-) battery to anything and start the vehicle.
Watch the sparks fly.
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Old September 5th, 2017, 07:20 PM
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Couldn't this be overcome by a simple ground fuse?
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Old September 5th, 2017, 07:29 PM
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Quote:
Originally Posted by rdavisinva View Post
The overkill you refer to I used follows the manufactures instructions.
Share any wire and gauge reading will be inaccurate.

The very worst thing you can do is run a separate wire from the battery to anything other than the frame.
If you use battery ground to anything other than the frame all the vehicle ground could try and use the directly wired device, in this case a VDO gauge.
And if it does decide to use the gauge as the vehicle ground source the gauge will melt and catch fire instantly.
Sorry I didn't mean any offense by that. I've just sold and installed many aftermarket gauges over the years and never had to install a freaking separate relay to power one. Especially one that is just a replacement of what was already there. That's what I meant by sounds overkill. What you did makes sense.

The install instructions are explicit about grounding (separate, >= 14 gauge, and no teflon on sender) but not about power (just fused). I think I am going to give Red90's advice a try first, 1 because it is most simple, and 2 it makes sense having the probe and gauge ground have matching resistance. Right now gauge is grounded separately to inside the truck, but that isn't good enough apparently.

Good call on the ground to battery, I never considered that (lose of ground elsewhere) situation.

https://www.vdo-gauges.com/media/ins...c%20Gauges.pdf
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  #20  
Old September 5th, 2017, 08:04 PM
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Quote:
Originally Posted by NPT90 View Post
Couldn't this be overcome by a simple ground fuse?
You could do that, but you'll never see it in any factory setup.
Keep in mind the ground will draw whatever it needs so a ground fuse could work fine or blow every time, just depends.
Heat could also be an issue for a ground fuse.

Quote:
Originally Posted by AdamSanta85 View Post
Sorry I didn't mean any offense by that.
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None taken, my friend.
Just trying to be useful and share.
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UD: "Just Power through it man!"
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