TR2/3/3A Weak headlight

[carpecursusII]

OK, so I was setting up my new front signal and head lights. When I turn on the running lights everything lights up properly around the car. When I turn on the headlights the passenger side head light and front signal light get very weak, but everything else on the car stays lit brightly. I have swapped head light bulbs around and I am using halogen lights.

I am at a loss here. Ideas?

 

[TexasKnucklehead]

If the passenger side head light bulb is noticeably dimmer, something is wrong. I'd start by examining the grounding bullet near the horn on that side. I'd also check the wire on the hi/lo (dipper) switch. A poor connection, or bad wire should be getting warm. You should be able to feel the place where the connection is bad. -But before you melt any wires, check everything you can. Be sure the grounding lug is secure and making a good ground connection. You might see if the high beams act the same as low beams because that would point you toward (or away from) a bad ground.

 

[TR3driver]

Having the one marker light get dimmer seems like a dead give-away to me. You've got a bad ground connection, probably between the grounding clip and the body. It's not a very well-designed joint, but adding a star lockwasher between the clip and body might help. The points of the star should dig through the paint and make a good connection to the body. I've been tempted to run a separate ground wire out there, but haven't done it (yet).

 

[carpecursusII]

The marker lights are fine as long as the headlights are not turned on. If I had a bad ground would it not manifest itself in anything else? Everything is brand new, including the dash rebuilt by Frank out in CA. I will check the switch tonight.

 

[TR3driver]

The RH headlight and marker light are grounded at the same place; a little clip on the ledge behind the RH horn. With that clip not grounded and just the markers on, the RH marker fixture gets grounded through the headlight filaments and the ground on the LH side. Probably some current flows through the turn filaments and to ground at the rear turn signal, too. But not much current (total), so very little voltage drop through the tortuous ground path.

But when you turn on the headlights, the RH headlight tries to draw a lot more current and now there is considerable voltage drop in the ground path. Result, both headlight and marker light are dim (because they aren't getting full voltage).

I expect you can see a similar problem with the RH turn signals, and with the high beam headlights. But nowhere except that clip is the circuit common between the RH headlight and RH marker light, and not common with something else.

Easy way to check, turn on the headlights and check the voltage between that clip and the ground terminal on the voltage regulator. I expect you'll either see several volts; or the headlight will get brighter when you touch the clip.

 

[joe kumpel]

I have to agree with "bad ground" suggestion. When I had same problem I simply "redid" ground wire coming
back from headlight to bracket on inside wheel well....instant fix.

 

[carpecursusII]

Well, it was in fact a poor ground. I guess I have things wired wrong, I was presuming the marker light was being used as then ground for both it and the headlight so I just connected those two wires together without the thought of having a grounding clip behind the horn. I will have to find a grounding clip from the big 3 as I know that this basket case will not have them. Thanks again to you all.

 

[TR3driver]

An alternative to the clip is one of the 4-way bullet sleeves, and a short jumper with a bullet on one end and a ring terminal on the other. At one time they weren't available new and all of mine were broken.