Help: How to wire the old gauges?

[southcoasting]

So I finally got my engine started yesterday for the first time after my major rebuild! Felt pretty good. I went through the troubleshooting standards on here and from Don’s bulletins after no start. Got my timing on point as well from the schematics on here which was great. Printed those out to leave in my binder...I am thankful for this community!

However, I did not let her run for long because I could not get my gauges to work. I wired them the same as how they came with the boat so now I am thinking they were wired wrong already. So I need help figuring this out.

These old gauges don’t have any labels/letters in back of them to indicate what is what. So I figured some of the more experienced heads on here know exactly what is what...I assume these old gauges had a standard for the left post and right post hence the lack of labeling...I posted a pic of the before and after...again, just trying to get an idea of what goes to left and what goes to right posts...Not the best pics but figured they would help to see what I am looking at...

Center is ammeter, left is temp gauge, right is oil pressure. On the left temp gauge, that one has 4 posts...I assume one is for lighting and the other gauges have no lights hence only two posts...I assume the extra 4th post on this temp gauge that appears to be connecting to light so that you can jump it to other gauges with lights?

BTW: I do plan on replacing these as well as all wiring in the near future...but for now, I just wanna get out there after a 5 year restoration of my boat!

I always run a search before posting but I could not find any about this one...

[joe_db]

Not enough info from the photo,. but here is a general tip:
USA standard sensors are a variable resistance to ground, 240 ohms at the low end of their range and 33 ohms at the high end.
A gauge will have the following connections:
1. Ground
2. + 12 volts.
3. The sender
4. The light (might not be separate from 2)

Metal case gauges will sometimes use the mounting stud for the ground, plastic gauges may or may not.
Here is some info on Teleflex gauges, which you have at least one of:

http://www.jamestowndistributors.com/userportal/pdfs/Teleflex/TMTechCat-Instruments%28v4_0%29Tech%20Reference.pdf

[southcoasting]

Thx Joe!

So basically, the standard wiring for gauges is to have the sender on left and +/ignition on right...Does that make sense even for these older gauges?

I am not sure what brand they are...I thought they were VDO...

[ndutton]

It may or may not be helpful but the turquoise gauge backshell color suggests to me it might be an old Teleflex gauge. The illumination lamp socket configuration does too. If true, the connecting post identification is molded into the backshell in small single characters: I=Ignition, S=Sender, G=Ground

The other two gauges, dunno.

[joe_db]

Thx Joe!

So basically, the standard wiring for gauges is to have the sender on left and +/ignition on right...Does that make sense even for these older gauges?

I am not sure what brand they are...I thought they were VDO...

Only for some/most Teleflex gauges. The others could be anything.
I would be tempted to start over from scratch with new gauges and senders.

[southcoasting]

Only for some/most Teleflex gauges. The others could be anything.
I would be tempted to start over from scratch with new gauges and senders.

Thanks Joe...I hear you on that...it is the future plan...but for now, just needed to get by and get my motor running and home to my mooring...

[edwardc]

Based on your first image, both of the non-teleflex gauges have a terminal connected to one side or the other of the ignition switch. These would probably be the +12v power terminals.

The large mounting studs connected directly to the cases are ground.

The one gauge has a lone black wire to the remaining terminal. This is likely the sensor. The other gauge doesn't seem to have anything hooked up to this terminal. Did it even work?

[joe_db]

Find your pressure and temp sensors. The oil pressure sensor should read 240 ohms to ground and so should the temp sensor with the gauges disconnected. With the engine running the oil sensor should lower immediately and the temp sensor as the engine warms up.
That will be step A in figuring this out.
This diagram applies to fuel, temp, and pressure gauges. Voltmeters just need +12 volts and ground. Ammeters are a special case that can be done a few ways.
There are other sensors than 33-240 ohm, VDO uses some different ranges for one example, and there are sensors with independent ground, sensors to drive 2 gauges, and 0-5 volt sensors. The diagram shown is the most likely to be found on an A4.