fuse box / bulkhead no power... Please help..

[bigfsh]

 I've recently purchased a 1987 3/4 ton 2wd. Ever thing was working like it should. On the way home one night the tail lights and dash lights just stopped working. I checked the fuses "good". I checked power to the tail lights from the rear forward and there is none . There is power going to the fuse box , but it isn't making it to the bulk head connector for the tail lights. There also isn't any power to the instrument panel connector. The brake lights are working so are turn signals and headlights. I'm stumped! Any info would be greatly appreciated..

[bd]

Refer to the 1987 Wiring Manual, pages 177 & 178, and Diagnosing dash lights that don't work in the Technical Pages section of the Forum.

Dash lights and running lights are powered through the 20-amp tail/courtesy fuse; dash lights are redundantly protected by the 5-amp instrument lamp fuse.  The tail/courtesy fuse receives battery power via one of the two fusible links that connects to the firewall junction block located directly above the engine's left valve cover. 

If there's no power at the tail/courtesy fuse, verify that the junction block has constant 12-volt supply, then check both fusible links and their connections to the junction block.  Otherwise, concentrate your efforts on the wiring between the fuse block and the headlamp switch, and the headlamp switch itself.  Also see How to make a Fusible Link.

[bigfsh]

Bd thank you for the input. I have 12v going into the fuse block and even at the tail/Courtesy fuse. It's losing power leading out to the bulk head . I can run a hot lead to the tail lights and they will come on . BUT!!! My brake lights will not work. I have a wiring diagram but you'll have to forgive me. I am not very good at reading them.

[bd]

With the headlamps ON and the headlamp switch rotated all the way CCW, do you have power on both sides of the instrument lamp fuse?  I think if you follow the '...dash lights...' link I posted you will narrow the cause and find the problem with the dash/running lights.  It's sort of a cookbook approach.  If you have specific questions as you progress, post them and we'll help you.

Are the brake lights inop a new problem since your initial post?  Did you bump the brake switch and knock it out of adjustment?

[bigfsh]

I will follow that link and get back with you in the morning. No new problems.. When I ran a hot wire directly to the tail light harness I had tail lights. When I hit the brakes,  no brake lights . I then removed the hot wire from the tail light harness, hit the brake pedal and my brake lights worked?

[bd]

Regarding the brake lights inop, check the ground splice and ground connections for both rear lights.  Also, check the bulbs and sockets for corrosion.

[bigfsh]

The brake lights work, only if the hot wire I jumped to the tail lights is disconnected? Sorry for the ignorance bd.  I truly am a "newb" when it comes to electrical .

[roundhouse]

On mine.  We tracked the problem to the bulkhead connector itself

We had power on one side but not the other

I drilled a hole beside it and snipped the problem wires on each side and bypassed the defective bulkhead connector

[bd]

The brake lights work, only if the hot wire I jumped to the tail lights is disconnected?  Sorry for the ignorance bd.  I truly am a "newb" when it comes to electrical .

bigfsh, don't be concerned.  Everyone starts somewhere.

I'll attempt to explain what I think is happening with your brake lights....  The tail/brake bulbs have two filaments - one for tail and one for brake (the brake filaments double as turn signal filaments).  Each bulb has three electrical connections.  One end of each filament is connected to one of the two metal contacts on the bottom of the bulb.  The opposite ends of the two filaments are connected together and attach to the metallic case of the bulb.  The case of the bulb functions as the 'third' electrical connection and must be in good contact with the vehicle frame, or ground, for the bulbs to illuminate when powered.  If the ground connection to the frame is broken or degraded, electrical energy sometimes follows an alternate, less efficient path.  Since one end of each of the two filaments are connected together and attach to the bulb case, when the case connection to ground is lost, power entering one filament may flow straight through the adjoining filament and 'ground' through the adjoining circuit.  When power is applied to the "free" ends of both filaments, electrical flow ceases, because it no longer has anyplace to go.

So, check your rear lamp and frame grounds.

[bigfsh]

Ok so here is what I did this morning . All wires are hot to the head light switch . The Grey wire to the instrument cluster is also hot .

[bd]

Dash lamp power runs from the headlamp switch through the instrument lamp fuse then directly to the cluster connector past an inline splice.  Do you have power on the gray wire at the cluster connector?  It's common to have poor connections between the cluster harness connector and the PC board, between the bulb sockets and the PC board, and between the cluster ground wire and the cab sheetmetal.

[bigfsh]

Bd just pm'ed you.

[bigfsh]

Hey round house. How did you determine it was the bulk head?

[roundhouse]

Hey round house. How did you determine it was the bulk head?

Checked and had power to switch on brake pedal. Followed that wire to bulkhead  had power on inside of bulkhead   By stabbing test probe in bulkhead

But no power on engine side on same wire
Then I put jumper wire from battery to engine side of brake light wire. Brake light worked


The prev owner obvuliouslly tried to fix it as every single light socket on the truck was brand new

We also had to replace the turn signal control donut in the steering Collum

It was bad also and the brake light power passes thru the turn signal controller before they go to the back


I spent 8 hours tracking it down and getting it all to work right



But it sounds like as someone suggested.  It may be a bad ground for the tail lights


You're on the right track.  Just keep taking it one step at a time   Following the power from the battery to the fuelsebox to the headlight switch thru the bulkhead to the lights


When you ran the jumper wire.  Did you hook it under the dash or under the hood ?

The bulkhead harness splits three ways under the hood
One for the lights in the back. One for the lights in the front and one for the engine

Find the harness that splits and goes to the back of the truck follow those wires to the bulkhead and test for power on both sides of the bulkhead


If your headlights and front parking lights work then it's probably not the headlight switch or a lack of power coming to the headlight switch

Do your front marker lights work ?

[76k104x4]

I had a 82 chevy and one night while driving down the highway my headlights went out. Turned out to be where the wires plug int the dimmer switch had shorted out and melted together lol. Not sure if that would cause problems with the tail and dash lights but it's worth checking out.