Rev counter stops working when I turn the lights on

Any help would be great! Thanks in advance

What have you done lately to the Car?  
This could be a bad ground.
Pin2 of the Cluster is usually brown and the main ground for the cars instruments.

But I have seen and heard of the car using other sources of ground via the cluster because the primary path is wonky.

Start by seeing if there is a voltage drop on your main earth (ground) from the battery negative to the engine, then the frame. If there is more than .05Vdc difference then start by cleaning the ground points if needed replace the primary ground from the Battery to frame and frame to engine.  New ends on the cables don't count.  VW used unshielded cables on the Battery to earth, these are subject to battery outgassing, road salts and debris.  I won't tell you about a crusty ground that I found on a car of mine, safe to say that at 50F on a rainy day the car wouldn't start.  After fighting this for a few months, I got mad and my 12" off set combo box wrench flew out om my wet hand and fell on the battery negative post, to the frame and SPARKED.  Needless to say that about 6 inches after the battery terminal end, I cut open the sheath, and the cable was fully corroded where as it wasn't a stranded braid it was a green ,ess of corrosion and stuff…

I have seen bad grounds to the engines cause the Starter to use the Cluster as a ground frying it.  I have seen Clutch cables as well being used as the main engine ground as well so the starter is iffy.  
On Airplanes, that I have flown I have see a Plethora of grounding issues with the proper function of gauges, and radios.

You can add a spliced ground from pin 2 of the cluster to a ground point behind the cluster X brace, I used a Scotch-loc wire splice, and a ring terminal to a pilot hole drilled, and then scuffed to bare metal. Stainless Sheet metal screw and a ring connector resoled a lot of flaky issues.  I have a how to improve grounds in the archive section, while they are for 90's Cabriolet, they also show you where to ground other things on the mk1 frame.

I would also say you should verify that you have Battery Positive on the Black wire as well on the cluster.

You should also take the time to RELAY your headlamps, using a kit you can buy off of Amazon, as that requires you to add new ground paths to your lamps, and using relays you off load the high current from your head lamp circuit, increasing the life of your switch, get brighter lamps.  

The fact that you are taking a ton of current off of the switch.

At last check and clean your fuses.

Thanks, that's a great base of knowledge for me to start with. I think the relay kit is a great idea and may solve the problem. Maybe a job during hibernation over the winter.

Broken brown wire in the engine bay at the back of the rocker cover, next to the fat earth cable going to the coil bracket.

Briano1234 said

What have you done lately to the Car?  
This could be a bad ground.
Pin2 of the Cluster is usually brown and the main ground for the cars instruments.

But I have seen and heard of the car using other sources of ground via the cluster because the primary path is wonky.

Start by seeing if there is a voltage drop on your main earth (ground) from the battery negative to the engine, then the frame. If there is more than .05Vdc difference then start by cleaning the ground points if needed replace the primary ground from the Battery to frame and frame to engine.  New ends on the cables don't count.  VW used unshielded cables on the Battery to earth, these are subject to battery outgassing, road salts and debris.  I won't tell you about a crusty ground that I found on a car of mine, safe to say that at 50F on a rainy day the car wouldn't start.  After fighting this for a few months, I got mad and my 12" off set combo box wrench flew out om my wet hand and fell on the battery negative post, to the frame and SPARKED.  Needless to say that about 6 inches after the battery terminal end, I cut open the sheath, and the cable was fully corroded where as it wasn't a stranded braid it was a green ,ess of corrosion and stuff…

I have seen bad grounds to the engines cause the Starter to use the Cluster as a ground frying it.  I have seen Clutch cables as well being used as the main engine ground as well so the starter is iffy.  
On Airplanes, that I have flown I have see a Plethora of grounding issues with the proper function of gauges, and radios.

You can add a spliced ground from pin 2 of the cluster to a ground point behind the cluster X brace, I used a Scotch-loc wire splice, and a ring terminal to a pilot hole drilled, and then scuffed to bare metal. Stainless Sheet metal screw and a ring connector resoled a lot of flaky issues.  I have a how to improve grounds in the archive section, while they are for 90's Cabriolet, they also show you where to ground other things on the mk1 frame.

I would also say you should verify that you have Battery Positive on the Black wire as well on the cluster.

You should also take the time to RELAY your headlamps, using a kit you can buy off of Amazon, as that requires you to add new ground paths to your lamps, and using relays you off load the high current from your head lamp circuit, increasing the life of your switch, get brighter lamps.  

The fact that you are taking a ton of current off of the switch.

At last check and clean your fuses.

That is impressive advice, I'm going to try to get my brain to remember that.  

I ran separate earth's to a main block near the battery then a strap direct to that.   Not pretty, but works (some components like the resistance the trip back through the bodywork, so doing this may give you more feed back through your radio)

The other thing that is known to fail is the headlight switch itself, as it has the dash light resistor built in, and drags loads of load through it, so it gets rather hot*

*it doesn't, it reduces the voltage to the lamps, and hasn't really got anywhere to send it, so it gets hot.

Mark1gls worked a treat, found the problem, fixed it..... thanks guys. Think I will still relay the headlights in the winter.

mark1gls said

Broken brown wire in the engine bay at the back of the rocker cover, next to the fat earth cable going to the coil bracket.

Any chance you have a photo of said cable? I have the same issue but the wiring in the bay of mine is spliced with a lot that I can't figure out!

Brown wire attached to the rocker cover, other end joins the same loom with the yellow oil pressure wire.


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mark1gls said

Brown wire attached to the rocker cover, other end joins the same loom with the yellow oil pressure wire.


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Brilliant thanks, I don't have anything that obvious, may need to start at the clocks and trace back from there. Never easy picking up someone else's unfinished project! 

Looks like I have wiring that has been added and removed as well as some inline fuses that I need to figure out as well!! 

Just to note. Mine was a brown wire with a white stripe. To the right hand side, rear (as you look at it) of the rocker cover