VDO Tach Wiring

chitwnvw · Post by **chitwnvw** » Sat Jun 30, 2007 5:49 pm

I am trying to get my VDO tach going. The backside has a positive, negative, ground and light spade.

First, what's the difference between the ground and the negative spade?

I have wired the positive to the coil and ground the negative. With it wired this way the car won't start. Why?

Now if I start the car and hook the tach up this way it reads correctly.

What am I doing wrong?

dingo · Post by **dingo** » Sat Jun 30, 2007 8:53 pm

I'm not sure about VDO, but I'm looking at a Veglia gauge which I use on my Bus. It has 3 terminals labeled: +, -, Ground. Ground goes to Ground, '+' goes to 12V source, '-' goes to the '-' side of the coil (where it receives the pulse, same as the ECU does on F.I.). I'm sure VDO would be the same.

Randy in Maine · Post by **Randy in Maine** » Sun Jul 01, 2007 3:45 am

Here is a handy site to go for wiring up gauges http://egauges.com/Inst_PDF.asp

TexasAirCooler · Post by **TexasAirCooler** » Sun Jul 01, 2007 5:20 pm

Positive is tach power
Negative is ground
G connects to coil

chitwnvw · Post by **chitwnvw** » Sun Jul 01, 2007 5:25 pm

BeetleWarrior wrote:Positive is tach power
Negative is ground
G connects to coil

When I hook it up this way my bus runs like garbage and the readings are way off, like I am idling at 200 rpms. It's a lot closer when I hook the - on the coil to the positive on the gauge and hook negative on the gauge to ground. But then it won't start hooked up that way. I got this thing off of ebay, I'm starting to feel like I got fleeced.

TexasAirCooler · Post by **TexasAirCooler** » Mon Jul 02, 2007 1:13 pm

Humm... According to the wiring diagram the G is suppost to hook up to the negitive side of the coil.

http://jvila.club.fr/vdo_how.html

Hope you get it worked out.

Post by **Amskeptic** » Mon Jul 02, 2007 3:24 pm

chitwnvw wrote:
BeetleWarrior wrote:Positive is tach power
Negative is ground
G connects to coil
When I hook it up this way my bus runs like garbage and the readings are way off, like I am idling at 200 rpms. It's a lot closer when I hook the - on the coil to the positive on the gauge and hook negative on the gauge to ground. But then it won't start hooked up that way. I got this thing off of ebay, I'm starting to feel like I got fleeced.

You might have a short/leak in the windings of the gauge. If "G" to (-) on the coil makes it run poorly, it is acting like a failing condensor. Failing condensors will not let the engine start, but it can run, barely. Do not play with leads in vain hopes of finding the magic elixer. What BeetleWarrior said, or bust.

(+) comes from any #15 source at the fuse box directly to the gauge.
(15 means ignition-on power only!)

(-) ground to sheetmetal in area,
(there is a multiple spade ground on fresh air plenum near wiper motor)

(G) good strong fresh wire no sharp edges or nicks in insulation to #1 (-) terminal on coil.

Illumination should have a (+) coming from any instrument illumination source (grey/red wire) and a (-) that is independent of the gauge (-).
Colin

chitwnvw · Post by **chitwnvw** » Mon Jul 02, 2007 6:59 pm

Got it working! Don't know what I was doing wrong, since it worked just the way you said:

Positve is tach power
Negative is ground
G connects to coil

I'll double check all my connections tomorrow in the light...otherwise I'll have to blame it on the incompetent installer.

Itinerant Air-Cooled

Itinerant Air-Cooled

VDO Tach Wiring

VDO Tach Wiring