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one dim headlight

jasonv

Sr. Member
Joined
Jan 7, 2002
Messages
355
Hi,

Well it looks like I have another issue with my new Painless harness. I have one dim headlight. The passenger side light is just a yellow glow, the driver side is nice and white.

I have tried a different headlight switch and if I swap bulbs the symptoms stay on the same side. A new bulb acts the same way. Any ideas where to look next?

Thanks,
Jason
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
49,370
Yes, an additional ground wire.

You've already done the main tests. Made sure it was not a bulb issue, and not a switch issue, so that usually leaves a wire issue. The wires are the same from the main headlight switch, but separate after the dimmer switch. However, with this being a new harness and all, I would go for the ground issue first, then worry about any potential bad wires or connections.

You can do a quick test by running a section of wire from the battery's negative terminal to the ground wire in the 3-wire connector on the back of the light. Just jam the other end into the connector and see if the light gets brighter.

Paul
 

broncotime

Bronco Guru
Joined
Jun 30, 2003
Messages
1,186
Loc.
Grapevine, Texas
Hi,

Well it looks like I have another issue with my new Painless harness. I have one dim headlight. The passenger side light is just a yellow glow, the driver side is nice and white.

I have tried a different headlight switch and if I swap bulbs the symptoms stay on the same side. A new bulb acts the same way. Any ideas where to look next?

Thanks,
Jason
Check the ground on the dim light. Wiggle the ground wire to see if the light gets brighter (or goes out entirely).
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
49,370
That's a quorum then (whatever that is) and practically unanimous!
Go for those pesky grounds.

What happens Jason, is that the welded and bolted seams between the body panels get rusty and lose some of their conductivity over the years. More so in old Broncos than in most vehicles it seems.
You might even end up having to run either a jumper wire to ground the core support to the fenders and the rest of the body, or simply run a separate ground wire from the light to another part of the body. Personally, I think grounding the core support is better overall. Should help with all the items mounted to it, and maybe even keep future rust to a minimum.
All the more reasons to make sure that your main battery and engine and body grounds are all new, in good solid clean metal, and pretty much connect every aspect of the vehicle together in one system.

The largest of course, goes from the battery to the engine block, as close as is reasonable to the starter motor.
There should also be a direct path between the battery to the body. Usually the inner fender is the most convenient, but just about any body part is workable.
From the engine, there should be at least one wire/strap to the body. The back of the intake manifold to the firewall is the most common and convenient place.
Then there should be (but rarely is) a ground to the frame. Whether a strap from the engine, or body, or directly from the battery's negative terminal is moot. Just get one down there. It can be the smallest of these, since not many things on a Bronco are grounded through the frame (fuel tank senders for one), but you should still have a token grounding plan through the frame.

Your Painless harness might have it's own grounds, and certainly more than the original had, but they all rely on your main grounds from the battery. And those are something that YOU have to put in.

Sorry if you already have all that handled, but it's important to bring up now and then.

Paul
 

Steve83

Bronco Guru
Joined
Jul 16, 2003
Messages
9,126
Loc.
Memphis, TN, USA, Earth, Milky Way
If it affects both hi & low on that bulb, it's a ground fault. If it only affects low, it's a power fault in the low circuit for that bulb.

With the headlight on & dim, put a voltmeter's black probe on the battery (-) and its red on the dim bulb's ground terminal (or pierce its ground wire). Anything over 0.5VDC indicates a poor ground. If not, move the red probe to the dim bulb's hot terminal (or pierce its hot wire). Voltage should be within 2VDC of battery voltage. If not, there's resistance between the red probe & the splice to the headlights from the beam select switch. Work the red probe toward the hi/low switch until voltage jumps into range - you just crossed the fault.
 
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J

jasonv

Sr. Member
Joined
Jan 7, 2002
Messages
355
jumping the headlight ground wire to the negative battery terminal indicates it's a ground problem, the light get bright like it's supposed to. I see a recurring theme here, perhaps someday I will learn. I guess I need to put a bit of work into my grounding scheme.

Thanks again all,
Jason
 
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OP
J

jasonv

Sr. Member
Joined
Jan 7, 2002
Messages
355
Problem SOLVED!!!

A ground wire, like many other things, works better if you, ummmm errr ahhh, actually connect it to something. ;)

Looks like I missed one when I connected the other grounds up there.

Jason
 

Viperwolf1

Contributor
electron whisperer
Joined
Aug 23, 2007
Messages
24,346
Just like in school, the shortest answer is usually correct.
 
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