Combo Gauge Wiring on a 70t

noob911t · 12-03-2004, 05:08 PM

This might sound dumb but I have searched previous threads and have found nothing specific to this question. I have a 1970 911t that came with the standard non- combo gauge set. I have recently purchased a combo gauge set from ebay and tried to install them. I managed to get the fuel level and oil temp to work ( as on the previous gauges) but the oil level and pressure just peg. The correct colored wires for the combo gauges seem to be in place behind the dash and are connected but still no accurate read?? Are the wires dead? Wrong? or may this be a sender problem? Any help would be appreciated!!!!!!

noob911t · 12-04-2004, 02:09 AM

Any one ??

jpnovak · 12-04-2004, 04:50 AM

Don't fret, Not too many people will post late on a Friday or Sat night. Just a reminder there is a search button in the upper right menu of this page. It should be your best friend in finding information.

I assume that your gauges are wired incorrectly. They range from no reading when open to pegged when shorted. Sounds like you may have 12V applied when there should be less. Use these wiring diagrams to verify the connections. Pay attention to #68 and #65 and their respecive senders.

Are you sure the connections in the engine bay are clean and in the right spot? Oil pressure will be lower right of the fan. Oil level will be on the oil tank in the fender. I would suggest removing these contacts and watching the gauge. If they continue to peg when they are disconnected the guage is wired wrong. IF they drop to nothing the problem could be a bad sender.

noob911t · 12-04-2004, 07:58 AM

Thank you for the advice and the diagram. I was looking at that particular diagram during my first attempt to wire the gauges. I got frustrated not being able to find most of the indicated colors. I then went to the 65 through 69 diagram and i found that it more closely resembled what I was finding behind the dash ( blue/yelllow being the 12 volt source I believe, Brown being ground, green -white/red being wires from senders) Plugged yellow/blue into the "+" Brown on to "-" and green-red/white into the the "G" on each respective gauge. Still the temp/level are pegged even with the wires off the senders.

feelyx · 12-04-2004, 12:18 PM

Did you also replace your sending units for the oil pres and tank guage? They will need to be replaced with ones that are a match to your gauges.

Hope this helps
Tim in Sac

noob911t · 12-05-2004, 06:20 PM

Have not treplaced the senders yet but, should that still make the gauges peg, wires on or off?

feelyx · 07:01 PM

While the engine is running, try touching the sending wire to the engine case to ground it out and see if your oil pressure gauge drops. Right now your senders are setup like light switches (on and off) you need senders that have a variable resistors in it (like a dimmer switch) more pressure=less voltage.

Hope this helps
Tim in Sac

keitho64 · keitho64's Garage

My 69T does not have the oil level sender installed so that still does not work. I had to install another sensor for the oil pressure and run a wire for it. In general if the gauge pegs when power is applied there is a ground somewhere. The easiest way to verify the gauge is to remove the wire from the sendor at the back of the gauge, turn the key on and observe the gauge. If it pegs you either have the gauge wired wrong or the gauge is bad. I doubt the gauge is the problem so I would verify the wiring. If you have a long enough piece of wire, connect it to the sendor and drape it around the car and connect it to the gauge. This will isolate the cars wiring and verify it you have a short.

Here is a link to a thread when I did this. Feel free to ask any specific questions after you see what I did. It still works like a charm.

Installing a combo gauge where there never was one