Alternator light is always on

Well excuse me! Is this a help forum or not? I answered the question from experience and so decided to recheck my opinion. I said resister instead of diode. If a diode goes bad the AL terminal will get full voltage. I reiterate; before replacing a 3AW unit chech the voltage is not above 8 volts MAXIMUM.

Jaguar affectionado and etc.

William:

This is simply incorrect. There is no resistor. The AL terminal is wired to one phase of the three phase AC side of the alternator.It will either produce 7-9V of AC (NOT DC), or it will produce nothing. If the AL lead is reading 12 volts, you are looking at the lamp lead, or you've miswired something somewhere. But at the alternator, the AL terminal will always read correctly. Note the way the AL lead is internally wired in the diagram.

Just a word of warning on checking the warning light unit. Thge alternator AL terminal must not produce 12 volts, a resistor drops it to 6-7 volts to operate the
unit, 12 volts will burn it out. check it first or you will just burn out another 3AW unit

Jaguar affectionado and etc.

David,

Mike Frank's brake light fix works. He did it to one of mine and solved the problem I was having like that. Flickering brake light is very common. I found on a former '72 E-type that I owned that putting the rubber boot on wrong would cause the light to come on. I had to keep them loose to keep the light from flickering.

As for the 3AW, check out www.coolcatcorp.com. They offer a solid state replacement for the 3AW. Very easy to install. It eliminates that POS 3AW can. And while you are at the Cool Cat site, do yourself a favor and get the spin-on oil filter adapter and the quick drain plug replacement. Install them when you do your first oil change. You'll thank me later.

Steve Weinstein, JTC-NJ
'70 XKE FHC
'69 XKE OTS
'84 Ferrari Mondial QV

First, your brake light. This is my very favorite E-Type fix. Without unscrewing the tops, slide off the rubber covers on your brake reservoirs. You will see a piece of wire sticking up from the center of each. Push each wire down. Pick each wire up with your finger tips and let it drop. It should move easily. Push it down. If it doesn't go down and come back up, the float is waterlogged. Fix is very simple. Remove the top from the offending cylinder. There is an aluminum tube under each cap. Pull the tube off (it's just lightly pressed in place). You will see the wire is pushed into a cork. Replace the cork with a cork from a wine bottle. Replace the tube, reinstall the cap and you're done. Since the cork is gone, polish off the bottle.

Alternator. I've done a detailed write up on how the system works, you can find it here: http://www.coolcatcorp.com/faqs/Lucasalternators.html

In a nutshell, if your voltmeter is reading more than 13V, then the light is giving a false reading. The light is controlled by the "AL" terminal on the alternator, which produces 7-9V of AC current. This current is used to open the 3AW relay, which switches ground on one side of the bulb. If the relay is bad or the wire is broken, the light will be on all the time. The 3AW relay is usually located under your heater box, above the voltage regulator, on the firewall. It's a silver can that very much resembles a turn signal flasher. Your's is either disconnected, or bad.

There is no problem with your alternator unless voltage is consistently under 13V.

Wow Jeff,
I learned more about the brake electrical system from your email that I could have from any book.
Thank you very much.

I going to try all your diagnostic procedures and I will let you know what I find.
Is there a way to test the ignition relay or do I just replace it, and is this available locally?

What color is your e-type?

Thanks again,
David

'70 e-type sII OTS

David,

Let's talk about the brake light first. That light comes on due to any of three switches completing a path to ground.

The first two are the switches off the floats on each of your two brake fluid reservoirs. Normally the fluid causes a float in the housing (integral to the tops) to float up keeping the circuit open. As the fluid level drops (something it shouldn't normally do) in either reservoir, the float goes down allowing the switch to complete the path to ground and lighting the light. The caps should have rubber boots on them that cover the wire connections. You'll notice that they have a little raised center. This accommodates the post that sticks up from the switch. An easy test to see if these are working is to turn on the ignition and depress each of the posts sticking up out of the caps separately (you can just push down on the raised center of the rubber boots). If they are working correctly, the light will come on when either is depressed and go out when you release it (provided the float is working and there is sufficient fluid). An opposite sort of test is to pinch the little rod sticking up out of the cap with your fingers or some needle nose pliers (you have to remove the rubber cover, but leave the wires connected) and pull up. With BOTH rods full up, the light should be out (provided source three isn't the culprit, more on that in a moment). Finally, to check the wiring itself, simply pull the two off either cap at a time (pull by the metal part of the connector part, not the wire so you don't pull the wire out) and jumper the red to the black. Again, with the ignition on this should cause the light to light.

The third way that light comes on is off a switch on the emergency brake. To see this one you need to remove the driver's seat and pull up carpeting on the tunnel on that side. It is a little two wire button type switch. When the handbrake is on, it releases the button allowing the circuit to ground to complete. The switch is adjustable forward and aft to adjust its position whenever the emergency brake itself is adjusted for cable stretch etc. It is not at all rare for this switch to work loose such that the brake handle doesn't depress the button sufficiently to fully break the circuit. Often also causes the light to flicker if it is close but not quite spot on. The fix is easy once you get access to it. You just adjust it forward to give the handle enough depression on the button to get it to break the circuit. Testing it and the wiring is basically the same as for the reservoir switches (when the button on the e-brake switch is depressed the light should be out, when released the light should be on).

Remember, all of this only works with the key on.

Now, as for the alternator light, the most likely suspect is the relay (4a or 2a, can't remember offhand, it's a silver cylinder with a green sticker that looks light a turn signle flasher unit) mounted just above your voltage regulator, under the heater box under the bonnet. It compares volts out of the alt. to battery volts and tries to detect an imbalance to "tell" if the battery is discharging. If is notorious for failing and I'd start there.

Let me know how it goes and call with any questions.

Jeff Klein
1970 SII OTS
(803) 649-0515, ext. 165

Thank You Stuart,
I'll check out the float

'70 e-type sII ots

I am not sure about the alternator light. Best to check that with a meter to see if it is a false signal or the real thing. However, the brake fluid sensor is notoriously troublesome and the float in the resevoir seems to be the main culprit in sending false signals. Many E-Type owners will tell you the same story. Better hands-on guys than myself can spell out exactly what to do or what to replace, but as starters in resolving that problem, I would turn to the unit in the plastic brake fluid resevoir on the firewall. It has probably gone bad. Good luck with your new car.
1974 XKE OTS
2000 S-Type V8