Dash lights not working

Hello, 

I've recently bought a MK1 GOLF 5 Door C diesel 

Few things not working 

Fuel gauge
Any of the little bulbs in the dash
Horn
Headlights
Heater speeds

I've replaced the ignition switch recommended by the previous owner but hasn't made a difference

Any pointers will be appreciated

Thanks
Josh  

You are going to need a DVOM (Digital Volt Ohm Meter).

All things mentions save for the Fuel Gauge and Horns are controlled by the X circuit (load reduction relay)

Do the parking lights work?  yes, X circuit.

The horn. First make sure that if you remove the horn and the horn honks with applying battery feed and ground to it that is beep beeps. If not, the horn is bad.  I have had to replace the horn a couple of times on my 81 Diesel Golf over the 20 years I owned it. So make sure it works before going any further.

The horns on the VW (or horn) works like this.

Is there12V DC applied to the horns straight off battery to one side through a fuse, 12V+ full time to one side of the horn (check both) but it is usually the non-brown wire?  As you need to know what side failing No 12V?  then Jumper 12V+ to the horn. and Mash the button.  Does the horn honk?  Yes concentrate on the 12V to the horn. If the horn is known good, then you need to check the ground circuit  from the relay to the Frame via the Steering wheel and shaft.

A lot  of times the Button on the slip or clock spring breaks and falls off or is worn down and not making contact It is on the back side of the steering wheel

When you mash the horn button on the car, you are completing the ground path to the relay in the Fuse Panel that starts on the frame as a wire on the Steering Rack mounting bracket that is attached to the Steering Rack gear box.

From the steering shaft gear box ground is applied to the Center steering shaft up to the buttons in the Steering wheel.

From the other side of the buttons the ground goes back to the Steering shaft horn ring, and back to the fuse panel on a single wire, that activates the Horn relay, to energize and apply a ground to the other side of the horn.




Steering rack mount to steering shaft gear box.


The Fuel gauge to test requires a 9V dc Battery,
Remove the rear seat bottom, and the cover over the Fuel sender.  You will see a single connector with a Violet/black wire.  Remove the connector.

Using a set of jumpers attach the Positive lead to the Violet wire, and the Negative lead to the Brown wire.

Your fuel gauge should then read about 3/4 to full.
If not then you have to remove the clocks or access them so you can test the Gauge.  Apply the 9V battery to
Pin 2 of your main connector or one of the studs on the back side of the fuel gauge and Positive to the other one

The fuel gauge should move, to 3/4 full, if not reverse the leads.  does it move?  No then the Gauge is bad.
If it moves then you have a bad sender unit in the tank or a broken wire to the Main connector on the bash or a broken trace on the Mylar on the cluster.

(You need to figure out where the Fuel sender is failing.)
Divide and conquer.

Clock lights go bad usually one at a time, but they are controlled by the X relay, and the Headlight switch.

Since you have headlight issues as well as other X circuits things,  you need to test the X circuit.

Before spending a ton of time one other things.

Everything you needed to know about the X circuit (load reduction relay)

https://www.vwvortex.com/threads/the-x-circuit-from-the-ignition-switch.6761577/

If your X circuit is good then you have to diagnose all the other stuff.

But the Console lights as well as the Head lights are controlled by the Headlight switch and a few fuses.

So start using your DVOM to see that the Headlight switch is getting power.  There are fusible links from the Main power cable to the Fuse panel that can be toasted.

The Heater Blower is controlled by the X relay as well

The heater blower needs +12 via the Fuse, and Ground.
The ground is applied to the main blower motor connector on the left side of the heater box Motor side of the connector.

The blower switch has 4 wires on it.  One supplies power to the Switch, and the other wires control the speed by using various resistors to apply different currents to the motor.  The Absense of resistance is
Motor on high speed.

So you can remove the Connector on the back side of the switch, and with a big Paper clip Held with Pliers, you can short the Main Power lead (IIRC) ir is a large red/black wire, to the other pins in the connector. If the Blower works, when Jumpering then your issue is the switch.  If not, then check for the Resistor pack, or the Motor as fubar.

The Ignition switch that you replaced allows the X relay to disengage when the ignition switch is in the Start position only, and should be on in the Key in and the first run position Not Start.