98 Need electrical help

[garover1]

Trying to find a common link between the radio, clock, interior dome lights. All of these are now not working after I removed an aftermarket phone hook up. All dash fuses are good. I've tried to find anyplace under the dash where the phone might have been spliced into a common power source but I got nothing.

[garover1]

Today when I started the enhine the key bezel light and the radio were pulsing and an odd sound was coming from under the dash on the passenger side. The cigar lighter does work so it's just the dome lights and radio not working and the key bezel stays lit all the time.

[Ron T.]

I'm new to this, just picked up my 97 Discovery last April. Question, when you mentioned the radio did you mean the radio or the radio lighting? From what i see in the Hayes manual, all of the cold (ground) side of the lights you've mentioned is controlled by multifunction unit, apparently a purple blue wire going into B/24/4. But, if I'm reading the wiring diagram correctly, there appears to be a splice point or terminal where not less than five purple/blue wires join. It may be that the phone lighting was tied into this point. It is interesting that the British controlled the lighting on the cold side of the lamps, rather than on the hot side.

[garover1]

The radio lights are the ones that are pulsing, the radio does not come on but I was assuming it was tied to the constant of the lighting. When I was further trying to look at everything today I noticed that as long as the radio was off and the dome lights were off the bezel light would work fine. As soon as either of them was turned on the bezel light would light up. If I turned on the dome lamp and turned it back off the radio would flash 10 or 11 times along with this lighting the disc changer would also pulse. I'm thinking it has to be a ground, but I have looked everywhere for a loose or broken connection but haven't found it yet. Any Ideas on where the splice you are referring to is? Or the control unit?

[Ron T.]

In my opinion, it seems that there may be a couple of problems. I'm at work at the moment and don't have my Hayes manual here, but I don't think that there should be any connection between the dome light and the other things, except possibly the multifunction unit. I haven't owned my Disc long enough to get to know where everything is, but I think the multifunction unit may be under the right hand dash panel. It should have quite a few wires going to it. The lights have power going to them all the time through there own fuses, the cold (ground) side of the lights are tied together through the splice and the ground is controlled by the multifunction unit. Unfortunately I do not know where the ground side splice may be located.

If anyone on the list has a schematic of the multifunction unit it would be a very big help.

Later tonight (I'm on Mountain Time) I'll see if I can figure anything further out from the Hayes manual wiring diagram.

[garover1]

that would be a great help

[Ron T.]

OK, I've had another look at the book, and the wiring information they give is clearly inadequate. The dome light, rear interior light, rear cargo light, and column switch (ignition switch) are tied together and turned on when the multifunction unit provides a ground at pin 1. The radio lights are grounded directly as the radio has it's own light control circuit (I think) and dims it's lights when the headlight switch is turned on. So there is no direct connection between the radio lights and the interior light.

The Hayes electrical diagrams are little help, they're missing too much.

While there isn't a direct connection, there is an indirect one that would be worth checking out. The radio light power and dome light power comes from fuse F8 in the left hand side fuse box under the dash panel. There is power on F8 only when the headlight switch is on. The multifunction unit is also connected to F8 at pin H, when there is power there then the multifunction unit dims (not turning off) as it appears to to sense the voltage on this line, A low voltage to the multifunction unit from fuse F8 would tell both the radio and the multifunction unit that the headlight switch is off so the lights would come on bright. When the voltage is high enough then the radio and other lights would dim.

My suggestion, replace fuse F8 (interior lights}. The information we need now is to find out if the lights act differently with the headlight switch on from the way they behave with it off.

Do you have a good voltmeter?