Alternator wiring

Chris Blunt · Post by **Chris Blunt** » Thu Sep 25, 2014 5:09 pm

hello chaps
I have a 65 4.2 and after fitting a new 11AC alternator and 4TR regulator I thought I might as well renew the 3AW relay that controls the warning light. I can't find the 3AW, its not under the heater box but I assume it must have a relay.

thanks in advance

Post by **1954Etype** » Thu Sep 25, 2014 8:45 pm

3AW wasn't fitted to the early 4.2s.

vee eight · Post by **vee eight** » Fri Sep 26, 2014 5:36 pm

If you do not have a 3AW the ign warning light is usually connected to the oil pressure switch. Also there will not be a wire on the alternator which is connected to the single lucar terminal which looks like an earth terminal but is in fact the supply to the 3AW.

Phil

Chris Blunt · Post by **Chris Blunt** » Sat Sep 27, 2014 6:09 am

Thanks Phil, Angus.
I see there is confusion on this subject on previos posts. The separate large red Charging light seems to be connected directly to the alternator wiring as no charge shows on the ammeter until the engine is revved up to over 1300 rpm then this light will go off and immediately the Ammeter shows charge in a fairly erratic way, I understand this ammeter fluctuation is normal at start up then settles down in time.
The small ign. red warning light at the bottom of the Speedo (I think) disappears as soon as the engine is started making me suppose this is indicating oil pressure not charging.

I am quite happy with the way everything works but still confused over the oil pressure switch supposedly controlling the charge.

Thanks Chris,

Post by **1954Etype** » Sat Sep 27, 2014 7:19 am

Chris, the oil pressure switch doesnt control the charge. It seems Jaguar didnt't get round to sorting out the charging light on the early 4.2s.

G0lfer · Post by **G0lfer** » Sat Sep 27, 2014 8:44 pm

I have a 65 4.2 which has been misfiring lately but after cleaning plugs and adjusting mixture (too rich) this is now fine. However the ignition light is now staying on and varies in brightness when driving. I have read that it is connected to the oil pressure switch but don't know what the effect of that is as I am a technoprat! Can someone explain in simple terms please?

Chris Blunt · Post by **Chris Blunt** » Sat Sep 27, 2014 10:29 pm

Hi,
I agree that the 3AW relay doesn't exist on the early 4.2 cars, but I would still appreciate an idea what controls the ignition light. None of the wiring diagrams that I have seen show this clearly,
Can it be that when the 4TR voltage regulator kicks into action the red ignition light has a equal voltage to its supply and therefore goes out?
I've only owned this car for 6 months, there is some beautiful solid engineering gone into the manufacture as one would expect froma Jag , my other car is an Alfa Spider which is a different story.
Thanks. Chris.

Post by **1954Etype** » Sun Sep 28, 2014 7:53 am

The 'ignition warning light' is controlled via an oil pressure switch. If yours is on or blinking, i would look to change that first.

Chris Blunt · Post by **Chris Blunt** » Sun Sep 28, 2014 8:48 am

Thanks, I'm still at a loss as to how an oil pressure switch has any corralation to the alternator no charge warning light. Chris

Post by **1954Etype** » Sun Sep 28, 2014 9:05 am

It doesn't

SEJohnson95 · Post by **SEJohnson95** » Sun Sep 28, 2014 9:51 am

It's just one of those quirks of the early 4.2s. Thank god it alerts you to something, a loss of oil pressure is something I'd want to know about fairly quickly. A simple test should be when you fire her up within a couple of turns the warning light should be extinguished. At least that's from my experiences with the 4.2. Oil pressure switches can be annoying little things, I remember hearing Richard talking to people about it at the club day.

Chris Blunt · Post by **Chris Blunt** » Sun Sep 28, 2014 9:53 am

Angus,
On the bottom of the Speedometer there are three warning lights
Ignition. Fuel. and Headlamps.
Are we agreed that the red Ignition lamp is in fact an oil pressure warning light? Thanks.

Post by **1954Etype** » Sun Sep 28, 2014 9:55 am

Chris Blunt · Post by **Chris Blunt** » Sun Sep 28, 2014 10:03 am

Glad thats cleared up, so back to the beginning, on the early 4.2 cars what did the 3AW relay replace? And where is it? Chris.

Mark Gordon · Post by **Mark Gordon** » Sun Sep 28, 2014 3:12 pm

On the left hand drive 4.2's, the 3AW is located just in front of the bulkhead beneath the heater box. I assume that RHD's would be the same.

vee eight · Post by **vee eight** » Sun Sep 28, 2014 3:16 pm

Chris

I have just been through this with my 67 which also does not have a 3AW.
So it is not just the early 4.2's which are affected.
As I understand it, Jaguar decided that there was no need for an ignition warning light as you have an ammeter. They were too tight to replace the speedo with a new type so left the ign warning light as it was. BUT customers would have complained if the ign warning light did not light up and go out when it SEEMED the alternator was charging. So they connected it to an oil pressure switch which made it seem that it was working like an ign light.
There is nothing that replaces the 3AW (which is by the 4TR control box & heater box) and no circuit that is connected to the ign light except from the oil switch.
So if your alternator is not charging the only indication is from the ammeter.
Hope this helps

Phil

Chris Blunt · Post by **Chris Blunt** » Sun Sep 28, 2014 3:58 pm

Phil
That's most helpful, and makes a lot of sence.

It's possibly my confusion is that I have a larger brighter ignition warning red light which is independent of the ignition (oil pressure) light within the speedo, this light which may not be standard is the same size as the green choke light, I'm sure this light is in series with the ammeter since the second the ammeter shows charge this light goes out instantaneously , no flickering.

I wonder if there is a correct wiring diagram for the early 4.2 pre 3AW days?

Chris.

Post by **mgcjag** » Sun Sep 28, 2014 4:46 pm

Yes there is a diagram......look in thr knowledge base section under documentation....u will see s1 4,2 wiring diag........Steve

vee eight · Post by **vee eight** » Sun Sep 28, 2014 5:55 pm

There are quite a few wiring diagrams. The one you want for the ign warning light circuit is from chassis no 1E50001 RHD AND 1E75001 LHD. This shows wiring for the 3AW and also for the oil switch to ign light.
The oil switch in the wiring diagram is called an ignition warning light pressure switch. Which is a good description for it.
I think that your extra ign light has been added to the car by a previous owner who wanted to have a normal ign light warning, but I am not sure!
Some E Types I have seen, have both 3AW and oil switch circuits. Confusing!!!

Cheers Phil

Chris Blunt · Post by **Chris Blunt** » Sun Sep 28, 2014 6:10 pm

Phil,
I had a look at the various wiring diagrams suggested by Steve, and couldn't see a solution. It's possible that my car when it was converted to LHD in 1969 had this extra ignition light installed then as per later 4.2 cars and the 3AW installed too? I'll go and explore and see if the 3AW is there somewhere as all the indications are there is one.
I did notice another non standard mod. The radiator cooling fan has a relay with the main supply fused directly to the battery.
Thanks for all the help, at the end of the day I do have good charge and it seems to be working correctly. Chris.

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