Temperature gauge doing funny things, help please...

[Oliver80]

Hi there I'm a new member here and I've a little problem with my '82 camper, I've done a 1Y engine swap and replaced most of the things the previous owner had DIY'd, now if I turn the lights on the temp gauge stops working, all the other dials are fine and the gauge is good with lights off. I've done all the normal things, replaced earths, connectors, new sensors and now I'm at a loss. Any help would be most appreciated thanks...

[MidLifeCrisis]

That does sound like the sort of odd behaviour that you get when you have a bad earth somewhere!
Does the fuel gauge act strange too or just the temp gauge?
Does the gauge needle just drop to the 'very cold' position?
Does the red flashing light flash at all while its doing this?
When you say 'lights on' - is that just side lights, or main lights or full beam (or all of the above)?

[Oliver80]

Hi there, the red flashing light only comes on at start up as does the oil pressure light and orange glow plug light, they all go away when the engine fires, the fuel gauge is fine it stays the same with either lights on or off. The needle for the temp drops to cold as if turning the ignition off when any of the lights are on (side, dipped, main or fog). I've rewired/removed all the after market 'bad' wiring and put in an ancillary 5 way fuse box direct from the battery to power the stereo, phone charger and cigarette lighter as these where wired into the interior light, don't ask why as I haven't a clue, like I said DIY'd. I've tried to get the loom back to as close to original as I can to make things easier...

[windy]

That sounds an awkward one. There is a multiple earth "crown" to the left of the fusebox that might be worth checking. Mine had quite a few corroded connectors which gave me problems, although not the same problem as yours.

[MidLifeCrisis]

My guess would be that your gauge doesn't have a good ground connection and its 'finding' one via the light circuit (probably via the gauge instrument lights that light the gauges when the headlights are on); this alternate path is working until you turn the headlights on, then the positive voltage on that circuit is 'removing' the ground and causing the gauge to behave strangely (hope that all makes sense?)
The problem is probably either going to be the earth crowns above the fuse box (as mentioned above) or the long white connector that plugs into the back of the gauge cluster (either are often the problem)
As an aid to investigating - you could try putting in a temporary earth connection by connecting the gauge ground terminal to a bit of bare metal and see if that 'fixes' the problem - that would at least narrow it down;
If you have the old style gauges (no Rev counter) with the temp gauge in the 12 o'clock position on the gauge cluster then take a look at the pic below ....... the ground terminal is identified on it - connect a piece of wire to this and the other end to a decent ground and see if that improves things (be careful that you get the right terminal - the pic is the back of the gauges as you'd see them if you looked through the windscreen - it'll look different if you are staring down from above while sat in drivers seat !!)

[Oliver80]

Cool I'll give that a go at the weekend, as the bus is in use most days.

[Oliver80]

Thanks for your help on this, I've run some auxiliary earths to the back of the dials and it seems to have cured it. I could probably do with a new ribbon at the rear of the dials, one will turn up though. I also found some burnt wires behind the fuse box so replaced those as well, mine still has an old style fuse box how easy is it to change it to a later one with blade fuses?

[MidLifeCrisis]

I imagine it would be technically possible but it would be a huge amount of work .....
..... better off cleaning up what you have I'd of thought!