1976 F-250 2WD 460 with C-6. After market ammeter and voltmeter guages ( along with one or two others) installed. Situation: While driving at night with headlights on and heater on 'medium' or hi and lights in low beam or high beam function , headlights drop out...as in...they go out. Tail lights and dash lights continue to operate with NO visible voltage loss or gain seen on either of the two gauges. I've replaced the headlight switch,dimmer switch and inspected all wiring in that circut for headlights and find NO breaks,shorts, or any other apparent cause. Is it possible , that while the heater is in operation that the circut for the headlights is over loaded?. Altenator is a 50 or 70 some amp output and Voltage Regulator is in good working order ( full feilded the alt ever so breifly and have tested out Voltage regulator). This is inhibiting my abilty to drive long distances at night as when I apply the heater , thats about the time the lights begin to go out but yet leaving me with running lights and dash lights. Any suggestions????

The Headlight switch contains a circuit breaker that is probably causing the problem

Time for you to do the headlight relay upgrade

http://www.danielsternlighting.com/tech/relays/relays.html


It's the only way to insure the headlights will stay on and only costs about $20.00 and a couple hours work

I thank you for your timely reply. Two things here: I neglected to make mention of the item that the headlights do not stay off....they will come back on but then go right out again by mere split seconds. So I presume that it is that circut breaker located within the headlight switch?. Two) The diagrams shown do NOT include the single lamp system ( i.e. low and high beam on each headlight- I do not have a four lamp system, its the two lamp system). I'm reasonably assured I can do the work , but a more specific diagram would be most helpful.
Thank You.

The wiring is marked for High-low

What ever you see for the extra 2 lights is used on the bulb connector for the 2 light system

One relay position for Bright and the other one for Low

That relay upgrade was one of the best mods I've done to my truck so far. It is worth the effort of rewiring and it is not that hard.

Okay....but.....do I still use the existing headlight switch or what?

Yes, you use the original headlight switch to control the relays. Just use the wire that used to go to the headlights as the wires to turn the relays on.
If they go out and come back, it is also possible the headlight wiring is shorting out, which also would trip the breaker.

The Headlight switch actually ends up being a switch that turns the power on to the relays to send power to the head lamps which now get power directly from the battery and avoid the HL switch all together.

That's the beauty of relays

Wow, thats a great article... thanks!

One more time slowly

Going on the information reeived here in this thread I have a few questions ( now that I have the time and the parts to do this with). I purchased the relays with the dual 87 tabs on them. So as to replicate the singel circut for the low and high beam on not one but two relays. I.e. one relay serves as the "switch" for the low beam side and the other relay serves as the switch for the high beam side. NOw...before I do anything that is gonna kill me or at the very least result in a melt down, I'd like ot be clear on one or two things. 1) Its possible and in fact pefered...if i read the schematic correctly....to continue to use the OEM headlamp switch. What I'd really like to know is at what point do you incorparate the OEM dimmer switch( floor mounted ) into the circut?
2) I have acquired all the 14 ga color coded wire to do this with. Situation: wire it all from the starting point?...i.e. headlamp switch or cut into it after the plug in?
and lastly 3) Is is at all possible or to any benifit at all to improve or modifiy the grounds on either of these two circuts in such a way as to take the ground back directly to the battery negative post?


Thank you!!

The headlamp switch/dimmer switch wiring is what you use to trigger the relay and you get acess to that where it heads for the radiator support.
You use the oem wiring to the relay mounted near the battery.

The Low beam wire on one circuit of the relay which actuates the power to the low beam

The High beam wire on one circuit of the relay which

Running a larger gauge wire to the battery - post makes more sense for some reasons but them so does, grounding it near the source makes sens as well.

Just clean up grounding connections.

Thank You; seems as if to me it might just as well be worth the effort ( since I took the time to figure the amp draw) to go ahead and run new wiring as well. Matter of opinion I suppose. This makes better sense than the way/manner I had in mind of just re-doing the entire two circuts with new wires and introduce the relays at the radiator support area. I'll let you know how it goes.

Thanks again

You only need new wiring from the relays to the headlights.

I buy wire like this at electronics wholesale places.
A lot cheaper than retail and the wiring has an automotive jacket for protection against grease and road grime.

I used a 14 gauge, 3 wire with silver/grey jacket

One thing to bear in mind with electronic type wires is the temperature rating of both the conductor insulation and the outer jacket...usually for the cold as opposed to the heat...vibration and low temps can cause cracking.

I used relays from a later model vehicle when I did my 86. That way it can handle the vibration, and already has the pigtail with it... It did make quite a difference on the brightness, and then has relieved the electrical stress on the headlight switch. For anyone that tows, I recommend doing similar for the trailer lights. Used to have trouble with the headlight switches burning out, this takes care of the problem.

It's been a while so bear with me. I did the full upgrade mod as per LMC Truck ( fairly inexpensive) total cost of about 40 bux. So far I've not been left hanging in the middle of a turn on remote back roads with no lights in a known deer area . So everything worked out pretty well. Thanks to all for the reply and the help. Huge bonus.

Glad to hear it worked well, thanks for letting us know!