First off let me say if you don't have H4 lights, you really should. There is no comparison to what comes stock in the US other than putting the lights next to a pile of dog crap.

On to the problem. The headlight install was a simple cut the harness and crimp on the new plugs. No other wiring disturbed. Wires are a direct match up. Ground to ground, low to low, high to high. Lights work perfectly. .. oh, did I mention they are BRIGHT!

You have the headlights on now and when you step on the brakes, the XM radio goes nuts and shuts off the XM tuner module. If you are on standard radio, ,it goes into crap sound mode (my own description, couldn't find it in the manual anywhere)

It has to be coincidence doesn't it? I mean the two systems aren't related except they both ground to the car.

Yes, I clean ALL my grounds every two years and put deoxit (100% strength) on them. Ground strap to battery is new OEM from Roger. Alternator is new and cranks out a steady 13.6 with a heavy load. It's none of that from what I can tell.

Perhaps Alan can weigh in here with a little electron wrangling.

Thanks,

 

The lights are grounded to MP-I (behind the ignition amps) and MP-II (next to where the headlight shaft goes thru the inner fender on the pass side).

The radio (stock wiring) is grounded to MP-V, the "mother ground" above the CE panel. Pretty hard for those to get cross-wired, or a bad ground on one to effect the other.

Do you have the same effect with engine stopped, and just the headlights and radio on?

Do you have a relay kit, or are the H4s wired direct to the stock wiring? (They are brighter with the relay kit, and you can also wire it so that low beams stay on with the high beams-- helpful if you live somewhere with both rabbits and deer).

Do some voltage checks: With the headlights on, check the voltage from either headlight ground wire to a separate chassis point (e.g. engine block or cross-brace bolt). Check it either at your crimp, or the headlight socket if you can get a probe in there without disconnecting it. There should be no more than a couple of tenths of a volt (i.e. 0.1-0.2 volts) on the ground connection.

Now find the radio ground wire, and check voltage to chassis the same way-- with headlights on and off, and also radio on and off. Same thing, should be very little voltage on the ground wire.

 

Jeff--

Curious what the dash voltmeter is doing through all this. Did you put megabulbs in? (easy and tempting) The lights draw current through the main feed via the jump psot connection, so thinking that extra bulb current draw might be dipping voltage below what the head unit is happy at.

 

I'd be investigating what the radio is connected to and the voltage levels on those supplies (assume you have both permanent & switched supplies and of course the radio ground. You don't say but I assume the XM radio was in and working normally before you added the H4 lamps?

Dr Bob's question on bulb wattage is important - H4 wattage is a little different anyway but not by much - unless you upgraded - if so try stock wattages as a test.

An experiment could also be to remove the bulbs and test the same case again - determine for sure that it's a current loading issue.

You might try cleaning all the connections at the jump post and at the studs on top of the CE panel.

As Jim says for the ultimate in H4 lighting, local relays get you more brightness and reduce CE panel loadings esp. with uprated bulbs. But at up to ~80-100W bulbs you should not have any functional issues anyway (while I wouldn't really recommend this for stock wiring long term - it should work).

Alan

 

I do have 80/100 in there with the stock wiring. I'll downgrade to standard bulbs once and see what happens. If it's a pain, I'll wire relays up (with help from y'all). Tried Herman's kit. 2 kits tried and neither worked. Wiring issues in kits. Returned them to Roger. Had Herman on the phone and we couldn't find the problem. It was like the power just stopped inside a wire on both kits.

 

Jeff, 80/100 bulbs should be fine, that's what we have in the S4 with no relays.

I like Dr. Bob's voltage-sensitivity theory. If that is the case then I would expect it to be worse with hi beams (more current), and worse yet when flashing hi-beams with headlights on (both low and hi-beam are on, lots more current). And better with engine running (more voltage from alternator).