No Dashboard Illumination

I have no lights on the dash, neither the cluster nor the heater/AC panel. All the warning lights work. The dimmer tests good. There is a short in the illumination circuit. (soon as the lights are turned on, the 10 amp fuse under the hood labeled "panel" blows) I can't tell from the wiring diagram in the FSM where the circuit plugs into the cluster. (which plug) Can someone get me pointed in the right direction. Electrical stuff is not in my skill set. Also am I going to have to remove the whole dash to chase this down?

 

Easy fix...



Sorry, I really just can't stop myself...

 

Bump. Anyone?

 

First off, my manual is for a 2000. So this might be not quite entirely accurate but is probably very close. The 10A fuse runs the lights in these these things, so there could be a short in any one of them:

• Gauge Cluster
• Hazard light switch
• Rear diff lock switch
• AC Switch
• Radio
• Pass Airbag switch
• Heater blower switch
• Automatic transmission gear selector
• overdrive switch
• cigarette lighter light
• ashtray light
• glovebox light

I would disconnect the battery, set a multimeter to read continuity, connect one meter lead to the load side of the panel fuse holder (with no fuse in) and the other one to a good ground. If there's a dead short, it should start buzzing at you. Then I'd go through each of the items above and start pulling light bulbs. If the meter goes quiet, you've found a candidate. Be sure to check the sockets where the bulb plugs in for stray pieces.

Alternatively you could set the meter to read resistance, but you'd have to constantly be looking at it. Although that might be less annoying than listening to it.

Hopefully that finds it. If not, we'll have to dig into the manual some more

 

The wire you're interested in is that G-R thing across the top and the grey boxes on the right. I *think* the IF1 connector is behind the left kick panel, and i think 3C (the grey boxes), is behind the instrument panel on the left.

 

Ox---Thanks for the reply. The truck is a 95, V6, 4x4, MT, no locker, no glove box, ashtray or cig lighter lights, no pass airbag. Heater fan, A/C, Hazard, Radio all work. Radio works & lights up. I need to find out which plug carries the wire that powers the lights in the gauge cluster & heater/A/C panel, & what color the wire is. The version of the FSM I have doesn't have wiring diagrams.

Edit: didn't see your post until After I replied. Based on the diagram you posted I will see if I can find the R/G wire & trace it to the panel fuse. Thanks again.

 

@RysiuM any thoughts?

 

First thing: save fuses and wires and MacGyver some kind of fuse substitute: 50W bulb (for Example spare H4) with wires attached instead of fuse. Just plug that lamp instead of fuse (this is where MacGyver part is). If lamp goes full power, it identifies short. If it glows it means there is a normal power draw.

You don't have glove box, so the power of that "Panel" fuse should be grounded through a dimmer only. Do you have rheostat type or electronic? Either way, first thing I would check is unplug the dimmer it (that is easy part) and test if fuse still blows. If it does it most likely means you have insulation of the wire broken, shaved by vibration or eaten by rodent. Either way this is not fun (see the wire routing below).

If fuse is not blown (or MacGyver lamp does not light full power) it means that one of the circuits has short instead of bulb. If you have electronic dimmer (3 wires), it could be dimmer itself, as it is powered from that fuse. If you have rheostat type (2 wires) and it is functional you should not blow the fuse if dimmer is in position "off".

If you have electronic dimmer you can test easy if it creates a short on the power. Simply unplug the electronic dimmer and short the connecting plug between contacts 2 and 3 (it is white/black and white/green). DO NOT SHORT GREEN/RED with other wires. So if you short contacts 2 (white/black wire) with 3 (white/green wire) you can either have fuse blow or your panel lights illuminated. If lights are illuminated it means your electronic dimmer gives a short between contact 1 = 12V (green/red) and 2 = Ground (white/black). If lights do not illuminate but fuse blows it means the same as above - one of the bulbs have a short. Which one is a matter of pulling and testing each one of them or going through J/B No3 route (see below).

Now if you have rodent-type short. You are looking at the green/red wire. It starts at engine compartment fuse box goes inside the loom through the firewall on the driver side. Just on the other side of the firewall grommet inside the cabin there are two connectors on that loom. One is smaller with 10 contacts but probably only 6 wires on each side. This is not the one . The connector you are looking for is big and bulky with 26 contacts and 21 wires on each side. It is called IF1. One of the contacts in the middle of the plug (contact number 8) has green/red wires: on wire on the engine side and on wires on the cabin side (if you have cigarette lighter illumination you would have two wires there). So looking for the short on the engine side you would need to disconnect that plug and test continuity from the fuse to the ground (make sure you test continuity on the green/red wire side, not on +12V battery side). You can't do the "power on" test because other wires in that plug control Tail Relay operation.

No short, that your rodent fed inside the cab

That green/red wire goes inside some loom under the windshield to J/B No.3 (junction box located up in the dash behind the instrument cluster. I hate that part. Access to J/B No.3 sucks. I had no luck to get to it from under the dash. It is just to high. Whole bunch of dash panels have to be removed to uncover that set of plugs.

If you unplug the center plug (it is called 3D) the wire from cowl (from the fuse) comes to contact 9. Contacts 1 through 8 have wires (same color) going to each bulb (see picture below). So if you dug so far to have access to D3 plug unplugged from J/B No 3 you can test short on each contact 1 through 8 to the ground.
Contacts are:
1 - probably empty as it is for A/T, glove box and ash tray illumination
2 - goes to electronic dimmer. If you have rheostat it is empty
3 - goes to radio illumination. It is not powering the radio, it just tells the radio to dim a display for a night driving. If you have aftermarket radio that is probably not connected (most aftermarket radios don't have that feature) and may be hanging out. So if you have aftermarket radio it is worth to check if this is not creating a short (then left hanging out) or connected to something that should not be connected.
4 - No clue what it is for - my diagram does not show it
5 - goes to dash meter illumination
6 - goes to A/C switch
7 - goes to heater/blower illumination
8 - goes to hazard light switch.

Now some pictures:
Diagram for 1995


IF1 location:



J/B No3 location:


IF1 plug


J/B No3 Plug 3D

 

RysiuM---Thanks, I think. Based on my electrical skills, this may be beyond me. I will read this over several more times & see if I ever really understand it. I removed the dimmer (2 wire) & it tested good per the FSM. Did not see if the fuse blew with it out. I will try that next. Do I understand correctly that the dash has to be pretty much dismantled to get to JB no3? Again thanks for the help.

 

First MacGyver a bulb + wires instead of fuse. You can use any headlight bulb you have on hand. It is healthier for the truck to light that bulb instead of blowing up a 10A fuse every time. Before removing the whole dash start with low hanging fruit first.
1. Unplug the dimmer and check if "fuse" lights up. If it still does it:
2. Unplug IF1. Remove the "panel fuse" and and "tail fuse". Check continuity between the fuse and ground. With that plug unplugged the "power side" contact of the fuse (shown as "1" on the picture below) should show open circuit and the other side (shown on the picture as "3") should show also open circuit. If it does not you are lucky (kind of) as you will be looking for damaged wire in the loom between fuse box and IF1. If this is stock truck (nobody messes with wiring) I think this will be most likely cause of your problem.

Fuse box in the engine compartment:



If all things checked out under the hood I would look for any "custom job" around wiring under the driver side kick panel. Maybe someone tried to connect additional lights or power outlet. Or maybe you have some kind of alarm system added. Other thing to check would be making sure the radio illumination wire was not used for any "funny" things or left dangled exposed. I would bet any of these thing would be culprit of of your problem. Unless really you have a squirrel nest under the dash. If your truck was not submerged up to the windshield the J/B No3 would be the last thing to go bad.

And still before disassembling the whole dash I would check each illumination bulb connector by unplugging the element (not just removing the bulb, but inplug the wire from the element) and check if the short goes away. Not many difficult to access thing: A/C switch, Heat panel, Hazard light switch - all easy to get to. The only more difficult place is dash meter - you have to take it out. But again, I bet this is the last thing to go bad. Unless someone put bad LED bulbs in there.

It is really difficult for me to diagnose from 6 thousand miles away but show your pictures, ask questions and I will try to help as much as I can.