Brights pop fuse

[Dleslie212]

Hello. I completed a wiring harness on my 1977 K10, and an now trying to figure out all the little small mistakes and gremlins I made during. I got the fuel pumps handled, but am now having an issue with the headlights.

Both headlights are new. The headlight sockets are new, as is the dimmer switch on the ground and the headlight switch in the dash.

With both headlights plugged into the sockets, the lows work fine. Switching into highs immediately pops the fuse, no matter if one headlight or both are plugged in

When disconnecting both headlights, and switching to brights, the fuse does NOT pop. The aftermarket sockets I purchased have three wires, and I performed a continuity test of all three female prongs on the sockets to determine which wire goes to which prong, and cross referenced that against the Painless book I got. I am 99% sure the wiring itself is correct, but if it were correct, the fuse wouldn't be popping :/

The weird part is that when I disconnect the sockets from the headlights, and perform a continuity test, both of the vertical prongs in the socket get tone to ground, even though only one of them is connected to a ground wire. The other two are connected to high and low beam

Help!

 

[Dleslie212]

So a little more info - the fuse does, in fact, pop when trying tonuse high beams, even if the headlights are disconnected

 

[Dleslie212]

Found it.

I left all the Guage cluster wires disconnected and pulled the gauges fuse, because I have a set of Digital Dakota gauges I'm installing. The high beam indicator is grouped with those and was shorting against another wire. Separated it, and headlights work!

 

[Bloodhound1981]

That was fast!

 

[Dleslie212]

Trust me, I've been trying to figure this out for a week, it wasn't fast lol

 

[Bloodhound1981]

Trust me, I've been trying to figure this out for a week, it wasn't fast lol

Ha well 1 hour from posting about the problem to solving it is still pretty good. My guess was gonna be that the floor dimmer switch was shorting out.

 

[RustyPile]

Let's back up to the beginning.. Headlights are not fed through a fuse.. The switch contains a circuit breaker.. The only fuse would be the fusible link on the main power distribution wire feeding the headlight switch and several other circuits and devices.. If you have the headlights on a fuse, regardless if it blows or not, the wiring is wrong.. Just exactly which fuse was blowing that "killed" the headlights??

 

[Dleslie212]

Let's back up to the beginning.. Headlights are not fed through a fuse.. The switch contains a circuit breaker.. The only fuse would be the fusible link on the main power distribution wire feeding the headlight switch and several other circuits and devices.. If you have the headlights on a fuse, regardless if it blows or not, the wiring is wrong.. Just exactly which fuse was blowing that "killed" the headlights??

It was the 30 Amp headlight fuse. I actually figured out what the issue was, a few posts up. I appreciate you trying to help tho!

 

[Ricko1966]

It was the 30 Amp headlight fuse. I actually figured out what the issue was, a few posts up. I appreciate you trying to help tho!

Idk what you've done,but the headlights are not supposed to be fused,they are on a breaker in the headlight switch for safety reasons. The breaker won't pop near as quick,and will come back whereas you hit a bump at 100 mph and something shorts for just a second,you are dead before you can change your fuse. Sounds like you have power to the headlight switch run incorrectly.

 

[Dleslie212]

The terminations were all pre-made on the wiring harness.

Everything works correctly now after isolating that high beam indicator wire

 

[Ricko1966]

It's not working right. Read this,not sure if the value is in this article didn't read 99% of it because I don't need to. https://www.onallcylinders.com/2023...ht-switches-and-how-to-clean-or-repair-yours/
Your headlight switch should have an internal 35 amp breaker dedicated to headlamps only. It's a safety issue since early 60's. Now feeding a switch that has a 35 amp breaker with a 30 amp fuse is not correct.

 

[RustyPile]

It was the 30 Amp headlight fuse. I actually figured out what the issue was, a few posts up. I appreciate you trying to help tho!

No, you don't have it figured out, and NO they're not working right.. Go back, read, and study my first post and the post made by Ricko1966.. I'll say this one more time.. IF you have the headlights on any fuse at all, regardless if it blows or not, you have wired them wrong.. If the harness is an aftermarket item, it's MADE WRONG.. If you created the harness yourself or modified the original harness, it's done WRONG..

And speaking of done -- I'm done with this thread...

 

[Dleslie212]

It's not working right. Read this,not sure if the value is in this article didn't read 99% of it because I don't need to. https://www.onallcylinders.com/2023...ht-switches-and-how-to-clean-or-repair-yours/
Your headlight switch should have an internal 35 amp breaker dedicated to headlamps only. It's a safety issue since early 60's. Now feeding a switch that has a 35 amp breaker with a 30 amp fuse is not correct.

Very nice article, definitely clears up questions on how that works.

Since the headlights aren't running through a fuse, what's the purpose of the headlight fuse?

 

[Ricko1966]

Very nice article, definitely clears up questions on how that works.

Since the headlights aren't running through a fuse, what's the purpose of the headlight fuse?

Post a picture. My 75 doesn't have a headlight fuse marking on the fuse box. The 77k pic I found on the internet does not list one either. I think you maybe looking at something wrong.

 

[Dleslie212]

A few pics of the manual that came with the harness, as well as the fuse box mounted. The fuse labeled Headlights is the one that kept popping previously, before I moved the high beam indicator wire that was shorting