Hi everyone. I'm a new Jaguar owner. I just picked up a '61 Mark 2 2.4 -- not my first old car or british car though. My gauges were working, but now the fuel, temp and oil pressure gauge are all not working. Are these all connected together? Where do I start? I checked the fuses and one fuse was blown so I replaced. The gauges did not come back though. It is still running a generator and positive ground.
Thank you.
Walter

 

did you check that the fuse you replaced didn't immediately blow again. i only ask because i wasted a day and half a while back because i didn't check again. *headslap*

 

Thanks for checking in. Yes, I did -- I've been there before

 

Yes, there is a common feed. Should be a green wire from the heater motor switch, and goes to the oil pressure gauge and the instrument voltage regulator and then a light green/black wire from the regulator to the fuel and water temp gauges. That is the flow on my S Type, the Mark 2 might be slightly different. My guess is a spade connector has come off the heater fan switch and there is no power to the rest of the gauges

I'm assuming you know that the Lucas fuses and typical US parts store fuses are not the same rating system? Just though I better mention it as you mentioned replacing a fuse.

 

I suspect it is the voltage regulator.
That is the common feed for those gauges.
It's not a common fault but I have replaced a couple in my 50 odd years of Jaguars.
Cheers

 

This keeps coming up on the S Type Register so I though I would repeat my warning there, here as well.


Warning ~ Fuse values


Remember that Lucas fuse values of 35 & 50 amp etc are old British 1 second blow standard.

Fuses you buy today unless you order specially are American Carry Current rating.

In modern fuse values you should select a fuse of approx half the value of the Lucas rating shown in Jaguar Manuals.

e.g. Lucas Horn fuse = 50 Amps. In modern US rated glass fuses you should fit 25 to 30 amp.

Failure to do this could cause a fire in our car's wiring in case of a short.

 

I changed the fuse with the same type fuse that was there -- 35 amp. I better check the Haynes Manual to see what fuse is supposed to be there. 35 years of British cars and you would think that I would've known the values are different
I found the voltage stabilizer and will be ordering a new one. I didn't check to see the voltage going in and out on it, but it is probably the culprit. The same setup is on my TR6 and my son's MGBGT. I have a spare one, but it is for negative ground and I need positive ground.
Thanks for the input. I'll let you know what happens when things get resolved (hopefully) after parts come in.
Walter

 

Walter
As far as I know the voltage stabiliser used in your Mk2 is not polarity sensitive.
I have changed polarity on lots of old Jaguars and never had a problem with the voltage stabiliser.
That includes my previous 6 MK1s and 6 Mk2s and numerous other cars belonging to local club members.
cheers

 

Thanks Bill Mac. Moss Motors has separate part #s for positive ground and negative ground cars. Does it have to be grounded a "special" way? The car has a new wiring harness installed and just want to be sure the p.o. had it installed correctly.
Thanks.
Walter

 

I've also checked with the manual and it says the fuse should be a 50 amp. I should be ok with the 35 ACC fuse, but I've put 4 of the 50 amp fuses in my cart along with a few other items I need.

 

The fuse doesn't care which way the voltage flows through it, the same with a light bulb.
(as well as most things)

 

Maybe I wasn't clear but I was talking about positive and negative ground on the voltage stabilizer, not the fuse.
I was just out double checking everything, and it turns out that the fuse I had popped in there was bad. It wasn't "blown" so you couldn't tell, but there was no continuity. I have still ordered the new voltage stabilizer just to keep as a backup -- I've had 2 fail over the years on other cars.
We'll see what else pops up.
Thanks for the responses.
Walter

 

The original voltage stabilizer was from before the days of solid state electronics. My guess is that it would be a wire wound around a bimetallic strip. If not, it will look something like the main regulator. Either way, it works by intermittently breaking the supply. This isn't polarity sensitive. I'd guess that the replacements, though they come in the old style case, are solid state and will definitely be polarity sensitive. With a good quality design, solid state should be more reliable. It should certainly be way cheaper to produce. I'd guess the cost of the new ones is mainly in reproduction of the old box.

 

Yes, the new ones are solid state packaged in "old style" casing. I was just out tuning on the car and the fuel and oil pressure gauges are now working
The temp gauge is not working though so I'll have to see what is going on with that.
Walter

 

The video says it all. It mentions, but doesn't show the old mechanical type.

 

gotta love youtube!

 

Peter is correct in his assumption that the original voltage stabiliser was mechanical with a bi-metallic strip making and breaking like the old turn indicators systems only somewhat faster. It was definitely not polarity sensitive
The similar system was used in the MK2 oil pressure gauges ie bi-metallic strip being adjusted by a diaphragm as pressure increased. Not too accurate! (and not polarity sensetive)
If more modern replacement voltage stabiliser systems using electronics are being offered, then it is essential to respect the polarity of the system.
Actually, electronic stabilised voltage systems are nothing new.
I remember making a stabilised 1.5-volt source for glow plugs in my son's model aircraft using a 12volt battery source somewhere around 1980.

 

The only mod I would further make are some pico fuses to protect the chip.They are the size of those caps used ~ miles of space. Then it's bomb proof.

 

Glyn
I would add diode protection and make it atomic bomb proof.
Cheers

 

I hope there are some capacitors or diodes to protect the chip in the aftermarket versions. There's more than sufficient space in the box (and margin in the price).