Headlamp Confusion 1969
 

The harness is new (LL).
When dash indicates high beam, only the outside lamps are on.

When dash indicates low beam (no bright indicator), both the outer and inner bulbs are on.


I don't think they can be plugged in wrong. 3 prong to the outer, two prong to the inner.
What do you think may be wrong? I'm pretty sure the harness is good.
Thanks for any help, Rick

At the high beam switch could the lt green and tan wires be on the wrong terminals?

The sockets on the inner (hi-beam) bulbs are single element type; the sockets on the outer (low beam) bulbs should be double element type. The low beam bulbs ALSO have a hi-beam element in them.

You could just have one element out of one bulb. Or you could have the sockets switched on one side with the wrong bulbs installed.

Do you think it could be a faulty dimmer switch? I'm quite certain I have the right bulbs in the right places.

Do you have the bulbs installed in the correct locations? Lo-beam bulbs outside; hi-beam bulbs inside.

I'll take a look at that Peterbuilt. I still have the old harness so I should look and compare and see if the new harness matches the old at the dimmer connection. The headlight switch is new too but I suppose there's a possibilty that it is defective.

Hi 7T1, Yes, I'm certain the bulbs are in the right place.
3 prong hi/lo outboard and 2 prong high beam bulbs inboard,

Any possibility that the dimmer switch is wired incorrectly?

Well I just went out and looked. The new harness has the same color wires in the same places as the old harness in regards to the dimmer switch. I haven't checked any continuity yet. This is baffling.

Have ordered a new dimmer switch in the faint hope that it may be the problem.

One more question:
I just checked the dimmer switch for continuity.

The center terminal (blue wire) is connected to the green wire but when the switch is switched, the center terminal (blue wire) then only connects to the brown wire with no power to the green wire.

Does this seem wrong? I am only guessing at this point but shouldn't the dimmer switch send power to both terminals at high beam and only the green terminal at low beam?

The power for either low or high beams comes from the headlight switch to the dimmer (Light blue wire)switch.

The dimmer connector is a three prong-

Power in and switched to either low or high.

Even if you could turn the plug around ( which isn't possible)- or if it was pinned wrong- it would not change the high beam indicator on when switched to the lows.

The high beam indicator is downwind after the dimmer switch but BEFORE it plugs into the factory connector at the firewall.

To me- it sounds as the high (lt green ) wire and the tan (low beam) are in the wrong pins- see pic-at the firewall connector.

VERY possible since the harness is new...




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Thank You Richard! I think you may have nailed it. I just checked the engine side of the plug and the wires seem to be in the proper locations there. I guess the next step would be to pull the fuse box and check behind it. Your explanation makes sense. I'll check it and post results. Thanks again!

Well darn. I just pulled the fuse box and it looks as though the wires are connected right. tan to tan and lt. green to lt. green.

Somehow the high beam indicator seems to be energized by the low beam wire. I really didn't want to have to pull the dash/column again and I'm sure I would have noticed something wrong installing the dash since the wire colors are stamped in the speedo housing.

I'd put a meter on it... when the high beams are on see which wire has power at the connector.

They could have connected the high beam indicator to the wrong wire- your fix could still be as simple as swapping the wire around in the pins- as the electricity doesn't care what color the wire is!!!

The only thing you have changed is the harness...



Richard

I think you must be right. The green wires are for high beam. One of the green wires leads from the dimmer switch directly to the high beam indicator. When the high beam indicator is on, there is no power to the green wire yet the indicator is on.

I'll have to look again at the back of the fuse box. Thanks for your help Richard. I feel like I'm finally getting somewhere.

Solved
 

Old post I know but just wanted to follow up since I finally looked at this problem again today. In case someone has the same trouble in the future. The cause of this malfunction was just the headlight switch not being grounded. As soon as I grounded it properly, the problem went away.