1988 Gti cab dash lamps

Just got a 1988 cab, but found out dash lamps aren't working.
1. Can someone supply a 1988 wiring diagram for this make/ model as I seem to have an extra yellow lead for the MFA and not sure if blue/ grey should go to 58b
2. Dash removed. All bulbs ok and continuity to connectors ok.
3. Light power is from blue/white to 4 way connector on dash. No 12v present when lights selected/ connected. 
4. Blue/white wire traced to near fuse box where it goes through a plastic connector then under bulkhead somewhere.
Any ideas why dash lights not working or where to find the supply?
All help (and sympathy) gladly accepted.
Thanks 
Steve

When you say dash lamps do you mean the illuminations in the clocks, heater panel, cigarette lighter and switches? Are your exterior lights working ok? Have you got any photos of the connectors you're on about?

They are dimmed by the wheel on the light switch have you wiggled that?

In the 88 they aren't fuses, and it is a Gray/Blue wire that runs from the Switch (roller) to every bulb in the car save for the Trunk.  It isn't a fused circuit per say but check f3.

on the light switch pin 30 RED you should have 12V+
On one side of the pot (roller switch) you have 12V+ and on the other it varies when you roll the switch from off to full on as it is full bright when off, and dimmed when it is full on.  If you have 12v on pin 30 and nothing on the sides of the pot, then you either have a switch issue.  As pin 30 is tied to one side of the pot.  The other side is the Gray/blue wire that feeds all the lamps.

It is quite common for one of the itty bitty wires to get nicked and burn through things….

Steve1973 said

When you say dash lamps do you mean the illuminations in the clocks, heater panel, cigarette lighter and switches? Are your exterior lights working ok? Have you got any photos of the connectors you're on about?

  all Dashboard (3 lamps), Heater, cig lighter, lamp switch light, fog and rear window heater illuminations not working. Exterior all ok (except number plate and fog lamp not checked as switch is in pieces in front of me now!) unable to post photos yesterday but will try later

mark1gls said

They are dimmed by the wheel on the light switch have you wiggled that?

  yes, rheostat between pins 58e and 58b seems to be ok 0.2 to 23.3 ohms

That may be you problem then. On mine there is a grey wire in 58e to the dimmer. It is fed power of the number plate circuit. Check fuse 20. Get your number plate lights working and you should get you illumination back. Check nothing is shorting to ground.

If I remember right the light for the light switch itself is on a different circuit and is illuminated constantly with the ignition on.

Briano1234 said

In the 88 they aren't fuses, and it is a Gray/Blue wire that runs from the Switch (roller) to every bulb in the car save for the Trunk.  It isn't a fused circuit per say but check f3.

on the light switch pin 30 RED you should have 12V+
On one side of the pot (roller switch) you have 12V+ and on the other it varies when you roll the switch from off to full on as it is full bright when off, and dimmed when it is full on.  If you have 12v on pin 30 and nothing on the sides of the pot, then you either have a switch issue.  As pin 30 is tied to one side of the pot.  The other side is the Gray/blue wire that feeds all the lamps.

It is quite common for one of the itty bitty wires to get nicked and burn through things….

 ahh we are getting somewhere now. 12v pin 30 or 58 switched 12v is not connected to pin 58e or 58b. Could wire a jumper from either 58 (12v lights on) or 30 (perm 12v) to 58e (simpler short wire just as a test) Switch P/ N is 100 890 005 09/2015  So not original. F3 OK. Got a query though as gray/ blue does not connect to blue/ white on my 3 dash lights connector, unless it loops around or is via a relay somewhere. 

If pin 30 has 12V+  and there are no dash lights, then you  could as a test jumper 12V to the gray/blue wire in the connector from pin 30, to see it they will light, but be sure to have a fire extinguisher handy, as a nicked wire and close proximity to grounding point will usually take 15 other wires with it…. I have had to debugger burned looms where the wires are all melted together….

If you have your Dash off, then you may want to inspect that gray/blue wire to see if there are is any charing..

I would use a fused wire as a jumper that is about a 5amp fuse one one side as they will blow and possibly save your wiring…

If you have a battery continuity tester or test lamp that is a safe way to do it as you can use a 9V dc Battery (safest way) and at the connector place the positive lead on pin 58B,,the negative to a chassis ground and see if the bulbs glow….

Briano1234 said

If pin 30 has 12V+  and there are no dash lights, then you  could as a test jumper 12V to the gray/blue wire in the connector from pin 30, to see it they will light, but be sure to have a fire extinguisher handy, as a nicked wire and close proximity to grounding point will usually take 15 other wires with it…. I have had to debugger burned looms where the wires are all melted together….

If you have your Dash off, then you may want to inspect that gray/blue wire to see if there are is any charing..

I would use a fused wire as a jumper that is about a 5amp fuse one one side as they will blow and possibly save your wiring…

If you have a battery continuity tester or test lamp that is a safe way to do it as you can use a 9V dc Battery (safest way) and at the connector place the positive lead on pin 58B,,the negative to a chassis ground and see if the bulbs glow….

guys, with your help, I think I have cracked it-
1. Jumper required on light switch between 58 and 58b to feed dash and aux bulbs. Found by slaving in a low volt  battery to grey/ blue and seeing 1 lamp light (only 1 lamp fitted as not enough current).yellow wire is earth so that will go to 58e. This cannot have been working for years. 
2. Grey/ blue wire on end of large multiconnector to dash is intermittent so dash end needs a clean and connector wire reseat. 
Thank all of you guys, fantastic support from you all.
Got a retro Bluetooth dab radio working and just waiting for dash refit- will send pics…..

Glad to be of service....