Possibly a dumb wiring question...

[J-440]

Here goes. I have an aftermarket dash harness and aftermarket gauges.  I have 5 gauges with electronic sending units.  There is a 12 volt hookup in  each gauge going to the fusebox.  There are also 10 other separate wires from the fusebox that call for hooking them up to each sending unit.  Why would I need 2 separate 12v hookups for each gauge? Does each sending unit require a 12v hookup from the fusebox?  I thought the 12v hookup from each gauge going to the fusebox also powers the sending unit. Lemme know something. Thanks guys.

[Charger4404spd]

One of the 12 v wires should feed the bulb inside the gauge.

[J-440]

 Each gauge has a ground wire, bulb wire, 12v source, and a sending unit source.  The aftermarket fusebox directions call for each sending unit to be hooked up as I described above.  But since I'm already using the existing 12v source that powers the whole gauge, why would I need more wires from the fusebox to power each sending unit?  The kit is a universal and it states that some of the wires will not be used according to each setup.  I just want to confirm with ya'll  before I start cutting wires that I may possibly need.

[oldcarnut]

Do your gauges have provisions to activate a 12V unit when a warning set point is reached?

[Rolling_Thunder]

what gauges and what wiring harness are you using?       

Usually the 12V goes to the gauge and the sending units provide a ground source - this alters the gauge readings.   

The fuse block has extra 12V outputs - is it a Ron Francis kit ? I'm just curious what you have that makes you think they go to the sensors that's all.   

Let us know what you're using and we'll figure it out.

[J-440]

 Its a Summit Racing universal wiring kit. Pretty much a  Painless kit.  Good stuff.  Each 12v source from the back of each gauge goes straight to the fuseblock.  I thought that this wire provides power for the whole gauge including the sending unit it is connected to. The gauges are all  Stewart Warner electronic and the directions for the sending unit don't say anything about a separate power source other than the 12v wire I just mentioned.

[Rolling_Thunder]

Ah - I see ---  it doesnt appear that they are 12V sources - they are signal wires that go from the gauges to the sending units.

The red/white wire will provide 12V to all your gauges. 
Brown wire will feed the lights on your gauges


lt blue / black will go from your oil pressure gauge to sending unit
purple / white will go from the tach to your coil (-) side
pink goes from fuel gauge to your sending unit
green goes from your temp gauge to your temp sending unit

Harness kits usually include these wires but they are bundled with the harness - they do not go to the fuse block normally - they go from the dash section to the engine section - see if there is indeed another end of these wires in the engine section. 

At least that's what I got from the instructions from Summit. If the wires are different colors let me know what they are - they should be labeled as well. Let me know what they are labeled and it'll be figured out - 

[J-440]

 Yeah I've got 2 sets of wires for each sending unit. 1 to connect from the unit to the fusebox then the other wire from the fusebox to the back of the gauge.  But since I already have the thick red wire that supplies 12volts to each gauge then why would I need another 12v wire for each sending unit to the fusebox? Those sending units don't draw that much power do they?

[Rolling_Thunder]

the sending units do not use power at all - they are a grounding signal.

What color are the wires you're looking at coming from the fuse block ?

Any way you can take a picture of the wiring as is? 


I think the wires you're looking at are the sending unit wires that go to the "s" terminal on the gauges - not 12V power sources.

[J-440]

 Thats what I wanted to know.  I did'nt think the units required their own power source...the gauge provides that.  Thanks again Thunder.

[J-440]

  On the stock headlight harness that connects to the bulkhead (very bottom harness) I have 8 wires.  I've connected 7 of the wires to the 7 wires I have from the Summit harness.  The last wire (black) is missing a connection but in the stock schematic for my car the black wire connects to a brake system warning lamp.  It would be slot "W" on the bulkhead connector labeled P5-18BK.  This is really not needed since I don't have a lamp? Thanks again Thunder.

[Rolling_Thunder]

This wire is not needed - if you want to hook it to a brake light warning sensor you connect one side to the switch and the other to the lamp in the dash. If there is ever an issue with the brake system you would know if you decided to keep it.