My name is Paul and purchased a 1985 xjs v12 he coupe Sept. past. Over last 6 months identified several issues that required attention. With the help of the forum most issues were resolved. Must say its been a interesting and most enjoyable experience. Few days ago my heater fan stopped working, then I noticed left side headlights were out, but on high beam all 4 lights are on. Reviewing forum noticed fan, lights and horn relays are grouped together. As such just tried the horn and needless to say it does not work.
How best to identity the underlying problem and resolve. suggestions most appreciated

 

I would treat them as separate problems initially.

Check fuses in the Black fuse panel in the engine bay #6 is the horn and the Head Light fuses are in there as well.

There are 2 heater fans, are both of them not working or just 1. Fuse #10 in the main panel and fuse #5 in the auxiliary panel are the blower fuses.

If the fuses are good then we can start tracing the problem.

 

larger fuses located inside above drivers legs smaller panel above passengers legs. all fuses checked and are in good working order. Have removed plastic cover over the 3 relays. Seems strange when fan stopped working[neither one works] how can you tell if one is working one is not?. headlights not working but when click to high beams all 4 headlights light up and horn which always worked is now silent. Within engine compartment other than a small panel with spare no other fuse panels located. attachments are of fuses inside cabin. Hope this helps. Thank you, Paul

 

The fuse box in the engine bay LHS, the fuse nearest the front, has a dual purpose: it fuses the electric radiator fan, AND the horn (this is a fuse in the circuit in addition to the one in the cabin fuse box). Interestingly, the wiring diagrams do not show it as fusing the horn, but it does.

 

Checked in line fuse by left headlight mounted on rad frame, looked good but installed a new one but no change

 

could the problem be the power source to the 3 relay switches? if so what's the best way to check with the meter?

 

tested horn relay no power either constant or key on just removing panel lower dashboard will see if I can identify any problems. on the lower panel there is a knob, what is it's purpose?

 

The knob is the dash light dimmer.

When you say no power at the relay which terminal are you talking about pin 85, 86 87

I have just noticed you have an 84 model it does not look like the voltage to pin 87 from the left terminal post is fused. With the ignition on you should have voltage at pin 85 86 and 87 voltage comes from fuse #11 in the main fuse panel under the steering wheel.

If you have no voltage at the relay go to the fuse panel and remove fuse #11 and check for voltage at the fuse panel you should have voltage on one terminal. If you have voltage ther use an ohm meter and check the fuse.