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Voltmeter

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Old May 11th, 2020, 13:13   #1
trhains
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Hi guys hope someone can help with my query,
just fit genuine Volvo Voltmeter to space under clock on 1990 240 GL.
Voltmeter works ok, took power from Cigar lighter, earthed to chassis earth behind centre console and took power for bulb from clock light above it, all good however noticed Rev counter does'nt work unless I turn rheostat for lights right down in which case instruments not visible at night. Speedo works, temp and fuel guage work as well as the clock, voltmeter illuminates.

Update, just been out to check lights again in dusk, centre console lights are working as well as new voltmeter light and they dim with rheostat, but clock and instrument cluster lights not working, checked fuse 16 was ok but changed it and still same problem.
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Old May 11th, 2020, 13:35   #2
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Was the rev-counter working properly BEFORE you fitted the voltmeter? If so, then you've disturbed something in the installation process.

I took a feed from the HRW circuit for the voltmeter on my GLT; the cigar lighter is accessory-live, the HRW ignition live. It might be worth trying to tap the input side of the HRW switch for the voltmeter and see if that fixes the problem.
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Old May 11th, 2020, 14:09   #3
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Quote:
Originally Posted by trhains View Post
Hi guys hope someone can help with my query,
just fit genuine Volvo Voltmeter to space under clock on 1990 240 GL.
Voltmeter works ok, took power from Cigar lighter, earthed to chassis earth behind centre console and took power for bulb from clock light above it, all good however noticed Rev counter does'nt work unless I turn rheostat for lights right down in which case instruments not visible at night. Speedo works, temp and fuel guage work as well as the clock, voltmeter illuminates.

Update, just been out to check lights again in dusk, centre console lights are working as well as new voltmeter light and they dim with rheostat, but clock and instrument cluster lights not working, checked fuse 16 was ok but changed it and still same problem.
Have all the lights (and the fuel/temperature gauges) in the cluster failed - or just the background illumination lamps? If so check fuse 13, maybe you disturbed it when you changed #16?

I think Loki is right, and there are two separate issues here: the rev counter and the clock/instrument lights.

It looks like you wired up the voltmeter light like this:



... in which case there might be two possibilities:

a. The voltmeter illumination bulb has a much lower impedance than the clock and instrument lights - and so is providing an easier path to the earth (-ve) return.

b. You have inadvertently created an open circuit from the clock lights onwards (the centre console lights are separate and not controlled by the rheostat).

... the second seems most likely if you have a Volvo voltmeter.

The rev counter sounds like a red-herring. There should be no electrical connection between the cigar lighter and the instrument cluster, or the lighting rheostat.

I'd suggest as Loki says and take the voltage you are measuring from an ignition-live feed; I'd probably run a wire direct to the fuse box and tap into a potential there.

Good fortune,

Alan

PS. It looks like the cigar lighter is an ignition live feed (on my earlier car anyway - I don't have a diagram for MY 1990, but Volvo didn't change things much), so that should have given a good outcome.

I notice above you say the fuel/temperature gauges still work, so it can't be fuse #13. I still think the rev counter issue is a red herring. Try disconnecting the voltmeter (pull fuse #1 for the cigar lighter (on my car)) and see if the rev counter problem goes away.

Last edited by Othen; May 11th, 2020 at 14:44.
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Old May 11th, 2020, 17:49   #4
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Hi thanks for you responses gents.
Alan, I just tried removing fuse 1 (cigar lighter) started car, rev counter works but still turns down with rheostat. Not sure what to try next.
Disconnected power from clock lamp to voltmeter lamp no difference.

Thanks Trev H
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Old May 11th, 2020, 19:26   #5
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Quote:
Originally Posted by trhains View Post
Hi thanks for you responses gents.
Alan, I just tried removing fuse 1 (cigar lighter) started car, rev counter works but still turns down with rheostat. Not sure what to try next.
Disconnected power from clock lamp to voltmeter lamp no difference.

Thanks Trev H
Hi Trev,

First question: did everything (rev counter, lights etc) work properly before fitting the voltmeter?

So, you are now back to the state prior to fitting the voltmeter (no voltage pick up for the voltmeter and no power for its illumination) - is that right? If so has everything gone back to the way it was before it was fitted? If no then what has changed?

When you say the rev counter goes up and down with the rheostat, exactly what goes up and down (the reading? illumination?).

There should be no connection between the rheostat and the rev counter - try pulling fuse #13 (check it is the same with your car) and see if the rev counter (and/or all the other instruments) stop working. The instruments should all go off (but not the background lighting) - if it doesn't there is a short between the rheostat and the instruments - probably a chaffed wire, that should not be too difficult to find.

... dinner time... more later.

Alan

Last edited by Othen; May 11th, 2020 at 19:44. Reason: Grammar.
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Old May 11th, 2020, 20:15   #6
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Hi Alan, I really appreciate your input and help.
As far as I am aware everything worked before I fit the voltmeter, although I hadn't driven the car for a couple of weeks. I'm sure I would have noticed if the rev counter wasn't working, but as far as the instrument illumination not sure as I haven't driven it in the dark since winter time.
The rev counter needle moves with the rheostat as you wind the rheostat to max the rev counter goes back to 0 as your turn the knob.
When it gets dusk I will go out to the car and check that all the gauges work and their respective illumination,
Thanks again
Trev H
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Old May 11th, 2020, 20:17   #7
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... continued:

So that is the rev counter, if it powers up and down with fuse 13, and all the other instruments do the same there can’t be a connection to the +ve side of the rheostat - if the tachometer and instruments don’t do that then there must be a short between the rheostat and the instrument cluster (should be easy enough to find, but a bit fiddly).

If there is still some causal connection between the rheostat and the tachometer and you have checked for a short on the supply side then there must be a -ve return fault. We’ll worry about that if we need to later.

Interior lights: are they all working now the voltmeter light has been disconnected? If so then the bulb must be a bit too powerful and is making an easy path to earth. If so you could either replace the bulb with a higher impedance or put a resistor in line.

If the lights aren’t back to their previous state then you must have disturbed something when you installed the voltmeter light, so just find it and fix it,then you can install the voltmeter light again.

Sorry about all that: more questions than answers at the mo. We just need to be methodical about this, get everything working the way it was to start with so we don’t chase the wrong error, then get the voltmeter fixed in properly. The way you did it to start with should work fine.

I don’t think this will be all that difficult to fix. Just take your time and be methodical. Change only one thing at a time and get yourself a notebook - write down what you change each time and what it affects things.

Stay safe,

Alan

Last edited by Othen; May 11th, 2020 at 20:46.
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Old May 11th, 2020, 20:45   #8
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Quote:
Originally Posted by trhains View Post
Hi Alan, I really appreciate your input and help.
As far as I am aware everything worked before I fit the voltmeter, although I hadn't driven the car for a couple of weeks. I'm sure I would have noticed if the rev counter wasn't working, but as far as the instrument illumination not sure as I haven't driven it in the dark since winter time.
The rev counter needle moves with the rheostat as you wind the rheostat to max the rev counter goes back to 0 as your turn the knob.
When it gets dusk I will go out to the car and check that all the gauges work and their respective illumination,
Thanks again
Trev H
Okay, the first thing to do is make sure the tachometer is doing what it is supposed to, so we fix the right error. Do the pulling fuse 13 (or whatever it is on your car) and see if the tachometer stops working, and all the other instruments go out as well. If that doesn’t happen find the short circuit from the lighting rheostat. Try this with the rheostat turned right down first, then with it turned up fully, if the tachometer still powers up without fuse 13 that confirms the short circuit theory.

Having established the above, does the tachometer work properly with the voltmeter disconnected - with the rheostat turned down and then turned up? If so that fault isn’t to do with the voltmeter, so we need to find it first.

Interior lights: find out what is and is not working. The clock and instrument backlights are on the same circuit (bit of wire) on my 1980 car the wires are all white - all 5 bulbs are controlled by the rheostat. The clock lights are probably 286/T5 bulbs, in my experience the holders are really fiddly and the earth return contacts are very unreliable, you can test them with a little jumper wire from the bulb holder to the back of the clock. I think the instrument backlights are probably BA7s, again really fiddly. If you haven’t done it already the instrument cluster only takes 5 minutes to pull out (about 6 screws), so do that and see what is happening with your multimeter or a bulb holder.

I think the heater control lights are probably on the same circuit, but a different piece of wire.

If it is an auto the gear indicator and the back seat light and on the un-switched side of the rheostat and should work anyway.

This is just a question of being methodical and eliminating the impossible (very Sherlock Holmes). Once we get everything doing what it is supposed to the voltmeter will be easy (as long as it works - did you test it before fitting it?).

Let me know how you get on.

Alan

Last edited by Othen; May 11th, 2020 at 21:00.
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Old May 11th, 2020, 21:36   #9
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Hi Trev,

This link may be slightly useful:

https://www.volvo-forums.com/t16395-...o-referenc.htm

I'm guessing the voltmeter is the same as the one shown in the pictures. Note that Volvo recommends connecting the +ve sensor wire to fuse 13 (wasn't that as for the instrument cluster?).

Alan
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Old May 11th, 2020, 21:48   #10
trhains
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Thanks Alan
I'll give your suggestions a try.
As far as the voltmeter is concerned I bought it on ebay and one of the pics was of it connected up to a 12v battery and it showed a reading of about 12v. It seems to work when fitted as it reads about 12v with ignition on and with engine running about 14.5 and reduces as you apply a load like heater fan or wipers.
regards
Trevor
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