Gauge wiring - Converting from lights to stock oil and water temp

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Joined
Aug 8, 2018
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Location
California
My Car
72 Fastback - 351C-4V, Fitech EFI, T56 Magnum 6 Speed
Hello,

I'm in the process of adding factory center gauges to my car that didn't have them. I have thing rebuilt where I want them, have the new sending units for gauges etc. When I wire up the oil pressure and water temp, but just max out. Right now I just have them wired with one connection to + and one to the sending unit. Guessing that's either wrong or I need a resistor in there somewhere or something like that. 

Can someone shed some like on how these should be wired?

Also, I would like to keep the idiot light for oil pressure. Any chance there is a dual sender out there so I don't need to T this one and add a second sender?

Thanks!

 
Did you replace the sending units (switches) with sending units for gauges?

Jason is correct, the gauges are powered through an instrument volatge regulator that is part of the main instrument cluster.

Your best bet is to contact Midlife and have him make up a wiring harness for you.

The second option is to use aftermarket gauges, there are several examples on our forum of how other members replaced factory gauges with aftermarket gauges. You can find them by searching the forum.

To have both the oil pressure idiot light and gauge work you'll have to install a tee at the sending unit location and install both sending units.

 
Thanks Don. Yes, new sending units installed.

I'm on a tight budget right now so just doing what I can to get this all working with what I have as there is so much to do. A new harness and after market gauges will have to wait for phase 2-3 of this build.

Thanks again.

 
Be careful as to what you consider + and - on each gauge as they usually are not marked. One side receives a 5V signal routed from the CVR on the back of the dash cluster; the other side goes to the sending unit. Be sure the sending unit is appropriate for gauges and not idiot lights. One (I believe the red/white wire for oil pressure) wire is also routed to the ignition switch for the idiot light proof-out circuit and that wire must be removed for the gauge configuration.

The ammeter lines are only found in the headlight harness that supports a tach (except 71, where the harness supports the 3 gauge cluster with standard dash). Be careful with those lines as they are not fused and are always hot. Since you are adding the 3 gauge cluster, you probably don't have the right headlight harness.

As for the idiot light and gauge for oil pressure, you'll need two separate sending units and separate wires.

 
Thanks for all the comments. I do have the correct sending units for gauges. I am also replacing the stock ammmeter with a voltmeter as that was cheap and seems more relevant.

I think I'll go ahead and switch to a solid state regulator as that should be more reliable long term and will give more consistent output compared to the older mechanical style. Maybe something like this. https://amzn.to/2LBpCCV. The actual regulator in that package probably costs a few cents but this is still cheap enough so why not as it's easier to work with.

 
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