Ignition switch on older analogue VDO gauge systems

[BruceK]

I'm tearing my hair out on this one. I've checked wiring continuity of looms including cleaning all connections etc. I'll disconnect everything from dash to engine including warning light control box, and clean wires and connectors including ignition switch terminals, reconnect everything and the dash gauges are spot on and accurate. I'll go for a cruise and get bumped around a bit (note: ignition key bundle includes cork float and a few keys but isnt heavy by any means. At least not like the wifes car keys which is a bunched mass that must weigh more than 100g), and the gauges go haywire. Temp over reads and oil pressure under reads. To me it sounds like a loose connection increasing resistance but all connections are sound.

The ignition switches are original and so 27 years old. Could these be causing voltage fluctuations to the gauges? Has anybody experienced this as I've driven some old bangers in my time and not found an ignition switch to be problematic in this manner. They seem to work or not.

Notes:
I've noticed my wiring is not exactly true to the manual because dash lights are on a separate single switch circuit and gauges alter slightly from when one ignition is on and the other is then turned on as if they are getting a double positive and mismatched. Yet the two circuits to the gauge cluster should be separate....? (All original wiring here with no DIY cockups to influence this.)

(note: one engine serves the house batteries and the other a common start battery but the engines are a 1 diapole system so in theory should have no effect taking power from another system as the sensors are isolated, and no gauge works unless the starter battery isolator switch is turned on.)

 

[Mr Googler]

Pair of Verados and a bolt on transom frame will sort it…..the simple solutions are the best solutions ?

 

[starfire]

Have a look at the battery negative connections to the engines & at the batteries themselves

 

[Portofino]

When I had one ( a 2003 kad 300 boat ) my Fr techie , a Fr equivalent of Volvo Paul of this parish told me the insulation in the loom next to the engines due to heat / time degrades and spurious gauge readings start to creep in . Resistance changes sufficiently to cock up the signal(s) .
Med temps mean I arrived at this point quicker than say the uk guys on here .
Yes we IR scanned stuff , replaced sensors , swapped stuff over from port to STb , cleaned contacts , and even fitted on loan new parts like gauges , ECU s the whole shooting match etc etc .

I had already had my mind made up to offload the boat at the end of that ( 2014 ) season anyhow , in effect wash my hands os the whole VP outdrive thingy and the buyers surveyor missed it . This was added to the ever growing disillusionment of the things .
So I do not know how it was resolved.

Goos luck with your new hairstyle btw

 

[vas]

Bruce, BOTH engine gauges do that concurrently, or sometimes one side others the other?
if both, doubt it's the key, have a look at the starfire's suggestion (which you've obviously investigated, maybe more work needed there?)

 

[BruceK]

When I had one ( a 2003 kad 300 boat ) my Fr techie , a Fr equivalent of Volvo Paul of this parish told me the insulation in the loom next to the engines due to heat / time degrades and spurious gauge readings start to creep in . Resistance changes sufficiently to cock up the signal(s) .
Med temps mean I arrived at this point quicker than say the uk guys on here .
Yes we IR scanned stuff , replaced sensors , swapped stuff over from port to STb , cleaned contacts , and even fitted on loan new parts like gauges , ECU s the whole shooting match etc etc .

Goos luck with your new hairstyle btw

I can replace the loom you speak of for £80 so that's no heartache. Routing the damn thing may well be though.

 

[BruceK]

Pair of Verados and a bolt on transom frame will sort it…..the simple solutions are the best solutions ?

You and PeteM can go jump in the Welsh Med, in February!

 

[BruceK]

Bruce, BOTH engine gauges do that concurrently, or sometimes one side others the other?
if both, doubt it's the key, have a look at the starfire's suggestion (which you've obviously investigated, maybe more work needed there?)

I will double check but cant for the life of me see where. Thanks for the confirmation.

 

[kashurst]

It could be the keyswitch - they aren't exactly brilliant, but new ones are expensive! I take your point they usually either work or they don't but after 27 years anything is possible.
It could also be the resetable circuit breaker in the black box on the engine. That provides the +v supply to the instruments etc. The circuit breakers are cheap so worth buying a couple of new ones see if it helps.
It could also be a poor ground connection in the loom/connectors somewhere.

 

[vas]

I will double check but cant for the life of me see where. Thanks for the confirmation.

big bugger earth strap between engines and bat negative loose on either end? although I'd expect more issues starting tbh..

 

[BruceK]

big bugger earth strap between engines and bat negative loose on either end? although I'd expect more issues starting tbh..

These engines start on the dime. Even after a lengthy session on the hard. Less than a second on the ignition.

 

[BruceK]

It could also be the resetable circuit breaker in the black box on the engine. That provides the +v supply to the instruments etc. The circuit breakers are cheap so worth buying a couple of new ones see if it helps.

I have a few spare, top tip, thank you

 

[BruceK]

It could also be a poor ground connection in the loom/connectors somewhere.

And that's just it. I have taken every plug, every gauge, every sensor apart / unplugged and given a good clean with emery paper and Hosa DeoxIt - D5S-6 - Contact Lube Cleaner Protector. Twice now. Start the engines up and check calibration manually against the gauges and everything damn near perfectly reported. Go for a spin or after a week or two everything goes out of kilter and we are back to square one with
77C being reported as 100C
50 PSI being reported as 30PSI
Fuel tanks showing full (or at least one while the other jumps a 100 or two litres)
14V reporting 11.8

More befuddling is you switch one ignition on and the respective guages for that engine come to life. Switch the other ignition on and the original gauges get new readings. vice-versa too. It's like the stepper motors in the guages get a double positive. One poor and the other good but that makes no blimmin sense to me either

 

[Seastoke]

Pair of Verados and a bolt on transom frame will sort it…..the simple solutions are the best solutions ?

If you like car parks

 

[BruceK]

Well, what a pallava. Formula dont use the Volvo gauge panels nor wiring loom. Instead they have their own with so called aircraft grade wiring. Which from what I can see is scaled up 1mm2 Volvo standard to 3.5mm2 /12AWG tinned wiring which is as stiff as rebar. Everything powered off a common bus positive and negative per ignition switch and all connections to the gauges screwed in to hold in place except for the few 52mm Volvo gauges which dont have this capability, just push fit. These being the Oil pressure, fuel tank and temp gauges. Bear in mind everything is on a bus bar and so effectively in parallel yet one poor connection to the stbd fuel gauge threw all these instruments out even across separate ignition busbar looms. Why a faulty connection on one gauge should have an impact on the other gauges in parallel on a loom is beyond me, how it affect the isolated loom even more so. I guess the fuel gauge senders have a common positive somewhere and a bad connection cause a voltage drop across the entire system.

 

[kashurst]

fingers crossed you got it.
tinned wiring is great but 3.5mm? You could always rewire it in 1mm and sell the 3.5mm for scrap value.

 

[BruceK]

fingers crossed you got it.
tinned wiring is great but 3.5mm? You could always rewire it in 1mm and sell the 3.5mm for scrap value.

I'm tempted. Its impossible to work with. It really is very stiff and trying to get it off a gauge to test connections results in peeling it off the other gauges too. Daft idea especially as it doesnt carry any current to speak of. But the whole boat is fitted out in this manner with looms as thick as my forearm in places and heating strips behind switches and panels to stop condensation. It's all a bit OTT

 

[kashurst]

for the UK yes, for Canada , Alaska etc, probably a good idea to provide a means to dry everything out.

 

[simonfraser]

set up a new supply to the dash / fuseboard if the V is already lower there than at the battery ?
corroded breakers ?

 

[BruceK]

set up a new supply to the dash / fuseboard if the V is already lower there than at the battery ?
corroded breakers ?

It's sorted now. Though why it was a fix is beyond me but there you go. One loose connection on a fuel gauge sent the other gauges haywire. Go figure?