Jaguar Repair: jag radio relay, radio relay, ohm meter

Question
I've read your previous answer regarding no power to a S3 XJ6 radio.  I have an '86 XJ6.

I have the same problem.  I've traced everything back to the radio relay but was not aware of the upsteam 20A inline fuse.

In your opinion, is the relay possibly bad.  Is a failed relay a known or common problem?   I removed the relay and opened it and it looks brand new -nothing melted or pitted or fused together.

I intend to check the 20A fuse but was wondering if relay failure is a common problem?

Answer
Hi John,
A relay is easy to test but impossible to look at the insides to make a determination as to good/bad.

Look at the pin numbers on the relay (if it don't have a diagram on one side). You will see that a simple relay has only 4 or 5 pins labeled #30/51 (power in), one or two #87 (power/s to load) and #85 %26 #86 (the electromagnet that operates the relay) Some relays put a diode in the #85/86 circuit, so when testing you may have to check it in both directions (polarity)

Only the later ser 3 XJ-6 had a relay. There are 2 in-line fuses, one in with the radio (20amp) and a (2 amp) in the console.

To test the relay you need several pieces of wire or test leads. Connect #30/51 and #86 to a battery (+). Connect either one of the #87 to any 12 load like a head light bulb or even a brake light bulb or a 12 electric motor. So that you have a load on it (not just an ohm meter)

Now that it is connected that way just take a wire and connect it to pin #85 and touch that wire to battery (-) (ground) and the relay should "click" and operate what ever load you had connected it to.

As for common failures, ALL RELAYS FAIL sooner or later but jaguar has many more bad connections of wires than any other failures in electrics.  Don't waste your time trying to diagnose by symptoms. Go to whatever don't operate and start testing.

It was common for a customer to bring me their car and say "If I do this it does this and if I do that it does this and if I do this and that it don't do anything. What's wrong with it?"
My standard response is "Just tell me what don't operate and I will fix it"

I found it best in most cases to start at what don't work (load) and test toward the power supply (battery) It is a 100% fail proof method. I erase everything the customer wanted it to be and everything I think it could be and everything it had been in the past and I always found the problem and was always surprised at what I find.

If you want a diagram of the radio circuit (Jaguar part of the circuit) let me know and I will post one on my web site for you to copy.

Howard