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Both headlights out-update

Wow, you got to love this group. 10 or so responses on headlight issues. However, no one answered my question as to where the headlight relay is and if the headlight switch has a circuit breaker builit in as in some vehicles.

Snoman, I checked the voltage at the battery with the engine running at around 2500 rpm and got 13.5 volts which I believe is normal charging voltage. Please correct me if I am wrong. I then changed both bulbs and everything works, that is both high and low beams now work. Conclusion: Both bulbs did in fact fail at around the same time. I will/ or my son will now "Drive happy". Thanks to all who responded. By the way, the comments posted caused me to re-think electrical circuits and I now realize that a short circuit would not cause the headlights to fail. Only an over voltage/regulator problem would do that. However, one final question: If this vehicle has a headlight relay, (which I can not seem to find), and I think it must, to avoid heavy wires to the lights and a heavy duty headlight switch, and if the relay shorted, would that cause the headlights to fail? I am thinking that if so, then the high beams would fail also. Just wondering, as the problem seems to be fixed for now.

Reply to
sf/gf
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You are correct. The actual number is 13.6, but close enough ...

I then changed both bulbs and

If the relay shorted ON, the lights would remain ON. If the relay coil opened, then the relay would not fire and the lights would remain off.

You're way over thinking this. The easiest solution is always the most likely problem. If the easy stuff doesn't work, THEN put on the Thinking Cap and analyze stuff until smoke pours out of your ears.

Reply to
Jeff Strickland

On Mon, 21 May 2007 00:40:47 +0000, sf/gf rearranged some electrons to form:

It most likely does not have a headlight relay. Saves the mfr. a few bucks per vehicle.

Why is it that people who don't understand electricity always say something is 'shorted' when there is a failure? If you meant: "The circuit from the headlight relay to the headlight bulbs shorted to ground" then the headlights would not light up. Or if you meant: "The circuit that pulls the relay contacts closed is shorted to ground" then the headlights would not light. But neither will burn out the bulbs. In fact, opens due to bad connections are much more common faults than shorts.

My 1970 Ford has headlight relays, only because I installed them to increase the voltage at the headlights (make them brighter) and to decrease the current that had to flow through 37 year old wiring and 37 year old headlight switch.

Reply to
David M

On Sun, 20 May 2007 21:27:37 -0400, David M rearranged some electrons to form:

Sorry, meant to say, if the *hot side* of the relay coil was shorted to ground, the headlights would not light. If the ground side was shorted to ground, then the switch would have no effect and the relay would be continuously energized.

Reply to
David M

IIRC, the '93 Ranger has the multifunction switch on the column in which everything is switched. The headlamp switch switches the power while the multifunction switch controls the circuit. Ford's electrical systems are designed with minimal sized wiring and switches. Resistance that is almost certainly present after 14 years will affect voltage/current available at several points in the system. The grounds are usually the first to be affected. The headlamps have a common ground for the group. Ford along with most auto manufacturers use a floating ground system - not a return circuit as is common in A/C circuits. In most older vehicles, you will get a variation in voltage at the load as the load on a circuit increases. I have seen this as being near normal in older vehicles. I won't argue the principals of electrical circuits with you as I know the theory as well as you. I am only pointing out what I see in older vehicles as a result of increased resistance in floating grounds.

Lugnut

Reply to
lugnut

Actually there is no exact voltage because it will vary with tempature. It could be as high as 14.5 in cold weather and as low as

13.2 or so in hot weather. Typically it should be in a 13.4 to 13.8 range with a warm engine after running for a bit. When you start seeing voltages of 14.0 and above when warmed up, you may have regulator issues because a atlernator can produce well over 16 volts when regulator goes bad.

----------------- TheSnoMan.com

Reply to
SnoMan

If by "fail" you mean "burn out" then the answer is heck no. People are infatuated with short circuits, so when I am troublshooting, I like tok say that it's already as shorted out as it's going to get. A headlamp takes full voltage on one side and a complete short to ground on the other side. When it's working, it's as shorted out as it can be. No matter how much stuff shorts out on the truck, you won't generate any extra voltage with which to burn out light bulbs. I hope this makes sense.

I am innocent on the thermal overload and relay questions, since I don't have the same kind of truck. I can guess the answers, but I'm not going to guess. That's how disinformation gets going in these groups. I can say this: I have not seen a car with a headlight relay in a long time. I had a

50 Chevy that had one. I think that's the last time I saw one. I have never seen a car that did NOT have a thermal overload on the headlights, but that's not something that I routinely look for on a car.
Reply to
Joe

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