fuel and temperature gauges fail with headlights on

An alchemy of sparks, copper wire and earth

Moderators: User administrators, Moderators

Luftmensch
Registered user
Posts: 24
Joined: 11 Oct 2018, 10:39
80-90 Mem No: 16738
Location: London

fuel and temperature gauges fail with headlights on

Post by Luftmensch »

Dear forum,
I'm a new owner of a 1983 T25 with a short circuit issue. When I have the headlights on the fuel gauge and the temp gauge cut out (fuel reads empty and temp needle does not register either). When the lights are off, the gauges function normally. I'm assuming its a short, but if this is a common problem then maybe there's a quick way of locating the fault. ... would appreciate any pointers.
Thanks,
Luftmensch

User avatar
clift_d
Registered user
Posts: 3290
Joined: 04 Oct 2012, 23:51
80-90 Mem No: 11695
Location: Hackney innit

fuel and temperature gauges fail with headlights on

Post by clift_d »

With any electrical strangeness like this it's always worth cleaning the earth crowns first before trying anything else. They're located on the left a-pillar below the dash and behind the wiring/fuse board. If you unscrew the fuse board from the van body you should be able to push it carefully to one side without unplugging anything in order to see the crowns. Unplug the various earth wires from the crowns and then clean the crown tabs up with a bit of fine grit sandpaper before reattaching the various earth wires again. Using a bag tie or similar to bundle the earth wires together as you take them off should help ensure that you don't miss putting any back afterwards.
1988 LHD T25 1.6TD Westfalia Club Joker Hightop syncro

Luftmensch
Registered user
Posts: 24
Joined: 11 Oct 2018, 10:39
80-90 Mem No: 16738
Location: London

Re: fuel and temperature gauges fail with headlights on

Post by Luftmensch »

Okay, Thanks, I'll try your suggestion. Also, I forgot to mention that the headlights seem dimmer than they ought to. I suppose this is just the short diverting current from the headlights.

User avatar
937carrera
Registered user
Posts: 3599
Joined: 05 Apr 2015, 19:29
80-90 Mem No: 16333
Location: N Yorks.

Re: fuel and temperature gauges fail with headlights on

Post by 937carrera »

It's not a short, it's likely a high resitance earth causing voltage drop and both symptoms
1981 RHD 2.0 Aircooled Leisuredrive project, CU engine
1990 RHD 1.9 Auto Sleeper with DF/DG engine

Luftmensch
Registered user
Posts: 24
Joined: 11 Oct 2018, 10:39
80-90 Mem No: 16738
Location: London

Re: fuel and temperature gauges fail with headlights on

Post by Luftmensch »

Ok, I finally got around to cleaning the earth terminals. I think I was quite thorough in going about it. Because of the irregular shape of the earth crowns and because they were in a fairly tight location, I found the best method was to remove the earth crowns themselves and use a soft brass wire brush to clean the terminals and the plugs. Importantly, this also enabled me to clean the corrosion off the back of the crowns which make contact with the body of the van. When I started the engine I was happy to see the fuel gauge functioning normally. It also seemed that the issue with the dim headlights was solved. Even the turn signals seemed to flash a less lazily. However, to my disappointment, after driving for about ten minutes (with the lights on, as it evening) the problem with the gauges recurred (neither the fuel gauge nor the temp gauge was registering).
Where to go from here?

I should add that in the past, the problem with the gauges had been somewhat intermittent, where the fuel and temp needles would for no apparent reason occasionally spring back to life for a minute or two and read normally and then return to their usual restful position.

User avatar
937carrera
Registered user
Posts: 3599
Joined: 05 Apr 2015, 19:29
80-90 Mem No: 16333
Location: N Yorks.

Re: fuel and temperature gauges fail with headlights on

Post by 937carrera »

Well, it sounds much improved. I think what you are left with is a poor connection on the feed side. Check the condition of the big connector on the bottom of the dash.

Do you have a multimeter ?
1981 RHD 2.0 Aircooled Leisuredrive project, CU engine
1990 RHD 1.9 Auto Sleeper with DF/DG engine

Luftmensch
Registered user
Posts: 24
Joined: 11 Oct 2018, 10:39
80-90 Mem No: 16738
Location: London

Re: fuel and temperature gauges fail with headlights on

Post by Luftmensch »

Could you be more specific please about the location of the connector at the bottom of the dash?

Yes, I have a multimeter or two laying around somewhere but not very knowledgeable with using the things. My brain generally shuts off when I hear the word "Ohms."

User avatar
937carrera
Registered user
Posts: 3599
Joined: 05 Apr 2015, 19:29
80-90 Mem No: 16333
Location: N Yorks.

Re: fuel and temperature gauges fail with headlights on

Post by 937carrera »

1981 RHD 2.0 Aircooled Leisuredrive project, CU engine
1990 RHD 1.9 Auto Sleeper with DF/DG engine

Luftmensch
Registered user
Posts: 24
Joined: 11 Oct 2018, 10:39
80-90 Mem No: 16738
Location: London

Re: fuel and temperature gauges fail with headlights on

Post by Luftmensch »

Just to be sure we're talking about the right connector .... so the connector you're referring to is the one which you accessed by removing the instrument panel in that tacho job right? But you mention it being located at the bottom of the dash, so the instrument panel need not be removed as itchy feet points out:
"you don't need to remove the dash to get at the connector, you can see it by looking up under dash and reach up from below, remove it and pull it far enough away to get to the wires."

Okay, I'm with you. On to the part with the multi-meter, right? .....

Oh, I forgot to mention that last night as I was laying in bed it occurred to me that perhaps the occasionally intermittent nature of the problem with the gauges could be related to a loose connection somewhere.

User avatar
937carrera
Registered user
Posts: 3599
Joined: 05 Apr 2015, 19:29
80-90 Mem No: 16333
Location: N Yorks.

Re: fuel and temperature gauges fail with headlights on

Post by 937carrera »

That's why I linked to the thread - you can decide which route to go to get access.

Poor connection is where I was heading, that's why I suggested you look at the connector, to make sure it's properly seated and not suffering from corrosion.

After that, then it's testing for voltage at each of the instruments that aren't working.
1981 RHD 2.0 Aircooled Leisuredrive project, CU engine
1990 RHD 1.9 Auto Sleeper with DF/DG engine

Luftmensch
Registered user
Posts: 24
Joined: 11 Oct 2018, 10:39
80-90 Mem No: 16738
Location: London

Re: fuel and temperature gauges fail with headlights on

Post by Luftmensch »

Okay, I'm back, thanks for your patience. I have removed the instrument panel (I thought it best to just remove it so that I could better visually inspect wiring in the area).
Everything seems okay: no abraded wire insulation; no loose connections, no real corrosion to speak of; nothing unplugged, everything on the main large connector seems in order).

Next?

User avatar
kevtherev
Registered user
Posts: 18830
Joined: 23 Oct 2005, 20:13
80-90 Mem No: 2264
Location: Country estate Wolverhampton Actually

Re: fuel and temperature gauges fail with headlights on

Post by kevtherev »

Next is more of the same.
It's a circuit issue
So when it happens again use the meter to determine which part of the circuit is failing
All the circuits are pictured in the Haynes
AGG 2.0L 8V. (Golf GTi MkIII)

Luftmensch
Registered user
Posts: 24
Joined: 11 Oct 2018, 10:39
80-90 Mem No: 16738
Location: London

Re: fuel and temperature gauges fail with headlights on

Post by Luftmensch »

Well, I did get 'hold of a multimeter, and I do have the Haynes manual, but I think you're assuming a bit too much competency, kevtherev. I think I need to follow on 937carrera's more specific guidance. What's your hunch 937carrera on where to check next, and how the hell do I put this d'mn multimeter to use in this context? (to date, my use of the device has been either as a doorstop or to check if I need to replace the batteries in the Walkman).

User avatar
937carrera
Registered user
Posts: 3599
Joined: 05 Apr 2015, 19:29
80-90 Mem No: 16333
Location: N Yorks.

Re: fuel and temperature gauges fail with headlights on

Post by 937carrera »

Hmm, no pressure then :roll: There's plenty of others on here who have more T25 experience than me.

I have an idea, but let's review where we are on the gauges. Are both not working at all now - if an intermittent problem has turned into a permanent one that is good news as it makes it easier to diagnose.

Do you have a clock in the dash, and is that still working ?

Can you also put your vehicle details in your signature (like Kev and I have). It helps us help you, I have been assuming it's an early WBX, but it might be a diesel and there are differences.
1981 RHD 2.0 Aircooled Leisuredrive project, CU engine
1990 RHD 1.9 Auto Sleeper with DF/DG engine

Luftmensch
Registered user
Posts: 24
Joined: 11 Oct 2018, 10:39
80-90 Mem No: 16738
Location: London

Re: fuel and temperature gauges fail with headlights on

Post by Luftmensch »

As far as pressure is concerned, a little would be a good thing. I mean when it comes to electrical stuff I'm eager to take on some challenges as long as someone can provide direction or specific tasks (with mechanical work or body work I have far less inhibitions).

Clock: none, don't think there ever was one.

On intermittency of the gauge failures: hard to say for sure. As I mentioned, a few days ago after cleaning the earth crows the gauges did work for a few minutes with the headlights on. Prior to that the they hadn't worked (at least not that I noticed) for a few weeks, but before that when I bought the van (last month) the gauges worked about 50% of the time with the headlights on.

Vehicle details: I will officially post later but they are as follows: 1983, 1.9L, water cooled, right hand drive, manual 4 speed trans., panel van with LPG option.

Incidentally, I might add that about 4 years a ago, the previous owner had some interior work done which included adding 6 touch sensitive LED ceiling lights. They're mounted in a carpeted ceiling covering. A blaupunkt bluetooth radio was also added.

If you could maybe assign me a particular multimeter (bearing in mind my lack of experience) task while I have the instrument panel off that might be a good next step for me.

Post Reply