headlights/dashlights stopped working

[BackCountry]

Hi, I replaced a fuel pump and water pump yesterday and everything seemed fine but then when I tried to turn my headlights on nothing happened, no headlights, no dashlights. Changing a few pump shouldn't affect the headlights I wouldn't think. However, the dummy lights on the dash do still work. I've checked all the normal fuses and none seem to be blown but I've read about fusible links. Are those the metal box looking fuses in my fuse panel and I've also read that there is a fusible link on the starter, is this accurate? I'll be replacing the headlight switch this evening, but I just want to know what else i should be looking for.

thanks again

[CipherLogic]

Hi, I replaced a fuel pump and water pump yesterday and everything seemed fine but then when I tried to turn my headlights on nothing happened, no headlights, no dashlights. Changing a few pump shouldn't affect the headlights I wouldn't think. However, the dummy lights on the dash do still work. I've checked all the normal fuses and none seem to be blown but I've read about fusible links. Are those the metal box looking fuses in my fuse panel and I've also read that there is a fusible link on the starter, is this accurate? I'll be replacing the headlight switch this evening, but I just want to know what else i should be looking for.

thanks again

Year? Mechanical or electric fuel pump/Waterpump?

Is there no power to the headlight/turn signal fuses?

Check the power on the juction block on the top middle of the firewall. It will be diamond shaped with 2 studs and a red wires on either side. There will be a fuse links on those wires if they haven't been removed.

[BackCountry]

sorry, no mechanical pumps, both. and the truck is an 86 K10 Silverado with a 305 in it.

And I don't see a fuse marked headlights so I just pulled them all and checked for blown fuses. that's another reason i was wondering about fusible links and if tht's what those metal box fuses were. cause they're not labelled.

[CipherLogic]

sorry, no mechanical pumps, both. and the truck is an 86 K10 Silverado with a 305 in it.

And I don't see a fuse marked headlights so I just pulled them all and checked for blown fuses. that's another reason i was wondering about fusible links and if tht's what those metal box fuses were. cause they're not labelled.

Did you check to see if there was 12v going to the headlight switch?

EDIT: I said turn signals in the previous post, ignore that.

Check the headlight switch for power and then power across the terminals when the plunger switch is pulled out. If there is no power going through the switch you may need to pull the switch and check it for continuity.  If it is a dud, its only like 15$ to replace.

[BackCountry]

I havn't checked power yet, it was pretty late when I discovered the headlight problem last night so will buy the switch regardless today. But just wanted to know what else to look for as it happened so suddenly and when i was doing other work on the truck

[bake74]

sorry, no mechanical pumps, both. and the truck is an 86 K10 Silverado with a 305 in it.

     Did you mean you have a electric fuel pump, or you do actually have a mechanical fuel pump ?

[bd]

Hi, I replaced a fuel pump and water pump yesterday and everything seemed fine but then when I tried to turn my headlights on nothing happened, no headlights, no dashlights. Changing a few pump shouldn't affect the headlights I wouldn't think. However, the dummy lights on the dash do still work. I've checked all the normal fuses and none seem to be blown but I've read about fusible links. Are those the metal box looking fuses in my fuse panel and I've also read that there is a fusible link on the starter, is this accurate? I'll be replacing the headlight switch this evening, but I just want to know what else i should be looking for.

thanks again

The 'metal box looking fuses' are auto reset circuit breakers for power windows and high-current accessories.  They are not part of the vehicle illumination circuitry.

The headlamp switch uses several tiers of electrical protection.  All headlamp circuits are protected by a shared fusible link.  Your truck has four fusible links (6" lengths of special thermal wire located at the 'hot' ends of major harness feeds).  There are two connected to the battery stud at the starter - there are two more connected to the junction block bolted to the firewall above the left valve cover.  Chances are high that a fusible link is damaged or loose. 

The actual "headlamp wiring" is protected by a non-serviceable, auto-reset circuit breaker that is integral with the headlamp switch.  The dash, tail and running lamps are protected by a shared 20-amp taillight fuse in the fuse block; the dash lamps are redundantly protected by a 5-amp instrument lamp fuse in the fuse block that is connected in series with the 20-amp taillight fuse.  The 5-amp fuse is electrically situated between the headlamp switch and the dash lamps.

A word of caution:
Fusible links are the electrical system's first line defense and exist to protect the vehicle from electrical fire.  Never eliminate or bypass a fusible link, or you risk burning the vehicle (and any structure in which the vehicle is parked) to the ground! 

For technique on replacing a fusible link, read How to make a Fusible Link by VileZambonie.

[BackCountry]

well I replaced the headlamp switch but there doesn't seem to be current to the switch. can't seem to trace where the power is supposed to be coming from. guess I'll look into those links. ty for the info everyone

[bake74]

well I replaced the headlamp switch but there doesn't seem to be current to the switch. can't seem to trace where the power is supposed to be coming from. guess I'll look into those links. ty for the info everyone

     If it is not getting power, use the electrical diagrams in the tech section to back trace and find out where the power is dropping off.

[BackCountry]

Just an update, after taking the tester throught the truck I found that the fusible link that splits in two, one going to the alt and one going to the harness on the firewall, was the wire I was looking for. It was broken at the starter so I tried hooking it up. it immediately blew the fuse.

After some thinking I ran a new wire and same result. Well one of the things I had done last week was to finally get my fuel gauge working with a new sending unit and rewiring to bypass the missing fuel selector switch(hooked pink/black to pink, that was all). I cut that connection and VIOLA!! I have headlights again.

Soooo, the short seems to be between these two circuits. I might just run a new gauge wire from the sending unit to the cab and see what happens.

[bake74]

     Look in the wiring diagrams located in out tech section, look up the 81-87 interior diagrams and you will be able to bypass the tank switch if you wish and still hook everything up properly with out shorting something out.

[BackCountry]

Yeah, I had it hooked up right, the problem has to be elsewhere. Might also be my tank selector switch, I know it's bad

[CipherLogic]

Use the continuity mode on a multi-meter. That wire is grounding out some where.