Yep me again 78 J10

[hawgwild]

Driving home last night I switched to high beams. They came on for a nano second then went out. Luckily I still had low beam. It's apparent that something is shorting out. I have a new switch. The high beam indicator was on. Where do I start to look oh faithful Jeep owners? Thanks

[tgreese]

Get your multimeter and the wiring diagram and trace it.

[hawgwild]

some people are gifted to being able to complete mechanical and electrical tasks. I, however, am not one of them. light bulbs, fuses, headlight replacements and ceiling fans are my pay grade. tracing a short with a multimeter is above my acquired skills. but thanks

[will e]

The high beam switch is a good place to start. If you don't want to do electrical tracing, simply swap it out. It's probably old anyways, easy to replace and pretty cheap too.

[hawgwild]

did that a couple months ago. my high beams were out before. Figuring since I just got the truck in June that maybe they were already burned out. there is supposed to be a 25 amp relay somewhere that i am going to search for tomorrow. I have the service manual but have been unable to locate the relay.

[Cecil14]

I've never heard of a relay for any of the lighting in our trucks, especially as early as '78. As far as I can recall (bit of a stretch), all of the headlight power (high and low beams), runs through the headlight switch. The high beam power then goes through the high beam switch as well, I believe. Someone correct me if I'm wrong, as I am not looking at the diagrams right now.

[fulsizjeep]

I've never heard of a relay for any of the lighting in our trucks, especially as early as '78. As far as I can recall (bit of a stretch), all of the headlight power (high and low beams), runs through the headlight switch. The high beam power then goes through the high beam switch as well, I believe. Someone correct me if I'm wrong, as I am not looking at the diagrams right now.

Correct.

I am not sure when this started, probably 86, but the fog lights are on a relay. That's the only thing I am aware of on relay.

[fulsizjeep]

The high beam switch is a good place to start. If you don't want to do electrical tracing, simply swap it out. It's probably old anyways, easy to replace and pretty cheap too.

Those foot switches took a lot of abuse being below the corner of the windshield and also below the fresh air vent. Read: water

[Cecil14]

What you could do, and would be highly recommended, is to put a relay harness for the headlights up in the engine bay. There are several members here that make them now, as well as plenty of aftermarket options if you do not want to build your own. That will take a LOT of stress off the headlight and high beam switches.

[hawgwild]

wow I like that idea about the relay harness. something is causing my headlights to go kaplooyee. I have replaced them twice since June of this year. and thanks to every one about the relay switch being non existent. that explains why I couldn't find it. if any one know where to get the relay harness I would like to know. I also checked my voltage output while running. 14.2 thanks all.

[bigun]

Change out dimmer switch, I had a 64 F-100 turn on the highs and the brights would come on then start flashing drove me crazy till I bypassed the dimmer

[Chubbinius]

There's quite a few choices out there. eBay, Aliexpress, Amazon, etc.

Here are some ideas-http://www.danielsternlighting.com/prod ... ducts.html about halfway down page

another-https://www.ksuspensionfab.com/store/p6 ... rness.html

off amazon- https://www.amazon.com/headlight-relay- ... ay+harness

another- https://www1.lmctruck.com/1973-87-chevy ... ht-harness

and a fellow on here named Mass was making some too viewtopic.php?f=34&t=16176

good luck!

[hawgwild]

thanks all for the good info...

[hawgwild]

I like the one from K suspension. looks easy to do

[rocklaurence]

IMO, make sure that they have the ceramic/high temp light connectors. I purchased a $30 universal harness but had to modify the harness t fit the truck. Plus, I hard-wired it into the OEM harness. Elliminating a potential connectin issue in the future-and is cleaner. However, hard-wiring it makes it harder to return it to original, if you ever wanted to. I also upgraded to H4 lamps with the amber LEDs rings that are tied to the blinkers [so cool]

[will e]

did that a couple months ago. my high beams were out before. Figuring since I just got the truck in June that maybe they were already burned out. there is supposed to be a 25 amp relay somewhere that i am going to search for tomorrow. I have the service manual but have been unable to locate the relay.

Howdy, sorry, I missed in your post that you had already replaced the dimmer switch.

And you've mentioned your comment about the relay above. Yep, no relay. You also mentioned testing out a circuit with a multimeter is above your pay grade. It's time to get a raise! If you are going to have one of these old rigs it really is good to know a bit about how the electrical system works.

And it's not really that complicated to learn. You don't have to understand 'electricity' or even the differences or calculations for Amps, watts, volts and such to be able to comprehend a basic 'DC' electrical circuit. The multimeter might seem intimidating but most of the time you just use one of the three most popular settings.

You indicate you checked output voltage while running. Here's the next steps for using the multimeter.
Disconnect the dimmer switch. Turn on the head lights (or course they won't come on). With the multimeter in DC volt mode touch the red lead to each of the three contacts while grounding the black lead from the meter. One of these will show voltage. It won't be a full 12 volts, don't worry about that, you are just confirming which one is the power source and that they power source is working.

Test the new switch. Yes, it could be bad. Remove the test leads from ground and power source. Change the multimeter to OHMs. The display will show 100% resistance since the two leads are not touching anything. Touch them together and the display will change and show zero resistance. You now know how your multimeter shows an open and close circuit. Touch one side of the multimeter to the post on the switch that corresponds to the 'power' input. Touch the other lead to each of the two other posts on the switch. One should show almost zero resistance and the other should show 100% resistance. That's because one side of the circuit is 'closed' and the other is 'open'. Push the switch and try again. The two sides should swap which is open and closed. If in either position both sides are 'open' then the switch is bad.

If you want to get a bit 'fancier' you can use the meter to confirm if the high and low beams are 'complete' circuits. With the multimeter still in the OHM mode and the power to the lights 'off' ground one of the leads and touch the other lead to the two positions on the connector that are not the power source. As you touch each one the multimeter should change from showing 100% resistance to 'almost zero'. Don't worry about the actual value, you are just verifying that the circuit is complete. Try this on both sides. If one of the two appears to be 'open' then you know you have a bad circuit. The next step I would take is go to the headlights. Remove both. Use the multimeter the same as you did on the switch and confirm the bulbs are good. With the dimmer switch connected and the lights turned on test that you are getting voltage to each of the sources. If you are not, the wire is bad or busted and you will need to trace it down.

There are obviously lots of good trouble shooting videos. Watch a few on the topic and you will see that troubleshooting is not beyond your pay grade.

[hawgwild]

Goodness! Lots of information to absorb. Luckily I have a friend who is a few pay grades above me and we did check all the electric concerning the lights. Interesting is that in a few days after my hb went out so did my low beam. I have since ordered a relay kit which will be here next week. And the excitement continues....

[will e]

You might find it is the ground. Normally if the lows work and the high's don't I don't suspect the ground, but if it was 'close' before it is possible the ground could carry the load of the low beams but not the high beams.

Of course it can also be the lights switch itself. They are pretty easy to replace and not too expensive.

The relay is a great idea. It removes all of the load from most of the circuit. I am trying to decide if I should go with a relay setup or possible just swap out for LED head lights since they use a lot less power.

[hawgwild]

My harness comes in this week. I can give an update in a month or so. Wait until I try to install an EFI!!!