Headlight Low Voltage Condition and Relay Question

[t6dpilot]

I have always been frustrated that my headlights on my 69 have been a little dimmer than they should be. I mean, I know why (they measure 9.5v on both sides of the fuse block) and just need to do a little checking of the various points in the circuit with a multimeter. So, I have a few minutes this weekend to give it a go and the first stop is the relay up under the front cowl.

Doh, I don't have the maintenance manual for the car at the storage location, so I don't know which of the three round relays belongs to the headlights. No problem, I will just pull each one and check the lights and when they don't work, that is the correct relay. Right? .....Wrong..... Each time I pulled a relay, I checked the lights and they worked all three times. Huh? Aren't those wired into the circuit so that if you pull one, the lights won't work?

I do have a fair amount of electrical knowledge, but this does not make sense to me. My plan was to check voltage and resistance at each point in the circuit back from the fuse block. Relay - Socket - Headlight Switch - Dimmer Switch - to see where I get close to 12v. I am getting a voltage drop somewhere and I figure it is occuring at some connection point. I am not looking for a solution here since I think I know how to go about checking this out. What I am trying to do is understand the relay deal with the lights still working when one is pulled. Thanks.

[edmayo]

Scott, where are these three relays you're talking about, if you mean by the fuse block behind the left side battery those aren't for the headlights, those are in order bottom to top, horn, fog lights, factory A/C. The headlight change-over relay is on the trunk floor behind the combo gauge, very near to the turn signal flasher relay. Power to the headlight switch should come directly off fuse #1, but it is only a junction, it does not go through the fuse. Start with the battery positive cable clamp, best bet is to take the cables out of the clamp and bead blast the clamp then wire brush the cable ends, then start with your plan of following voltages along the circuit. Have FUN

[t6dpilot]

Thanks for the reply Ed. The relays to which I am referring are behind the flasher relay in the exact place you mentioned. There are three of them up there. Not sure what they are all for since I have not looked at the manual yet. It is not the relay down by the fuse panel.

I will follow your positive battery suggestion, but it looks visually in very good shape. Plus, I am getting 11.5 volts at other points on the fuse block. Because of that, I am assuming that the voltage loss is somewhere else in the circuit. Let the fun begin.

[911quest]

Scott,

When your checking voltage and getting 9.5volts what are you using for your ground point?

[edmayo]

Scott I should have looked at my 69 wiring diagram first, it shows the three relays where you mentioned, one is the headlight "flasher relay" , one is the relay for the blower motor, and.....are you ready for this, one is the relay for the cigarette lighter. I'd forgotten that 69 is the only year to have a cig lighter relay. I had run into that on Bob Aines's car when we trying to get power for his electronic accessories. In later years there is a relay in that area for a heated windshield which I didn't think you had, that is why I questioned where you were seeing the relays. I think that the headlight relay only affects the 'flash' function however. Pull the relay and see if it disables the flash function.

[t6dpilot]

Tony, I used a fender bolt if I remember correctly. I also used that same ground point when I got the 11.5v reading.

Ed, yeah these 69's are an electrical anomoly aren't they? Thank you for the clarification on the relays. When you say flash, do you mean the high beam flash when you pull back on the turn signal stalk? Thanks.

[JohnT]

Don't forget to check the quality of the grounding connections in the headlight circuit (or any other circuit in these old cars). Poor (rusted) chassis grounding connections cut the voltage too an are not uncommon in our old cars.

johnt

[t6dpilot]

Yeah, I have that on my list of "to do's." Any ground connections that I should check in particular?

[911quest]

Most of the time most voltage drop issues seem to be from a bad ground. If I suspect a a voltage drop I always recheck with the ground lead at the battery or the engine or transmission case. Have you removed the headlight to see what your voltage is that point? A simple test is the just make a overlay that you can run from the battery ground to the light to see if it gets brighter.

.

[edmayo]

Yes Scott, the lever pull back flash is what I meant.