If your 1997-1998 Ford F150 (F250 or Expedition) is currently experiencing a ‘no dash lights’ problem, then this tutorial will help.
Although this tutorial focuses on testing the instrument panel (IP) illumination lamps dimmer switch (of the headlight switch), I'm also gonna' offer you some testing suggestions if you're having an electrical short blow the #18 fuse of the under-dash fuse/relay box.
Contents of this tutorial:
- No Dash Lights Troubleshooting Basics.
- TEST 1: Making Sure Fuse #18 (5 A) Is Not Blown.
- TEST 2: Making Sure Fuse #18 Has Power.
- TEST 3: Bypassing The Instrument Panel Dimmer Switch.
- TEST 4: Testing The Dimmer Switch's Ground.
- How To Make A 5 Amp Fused Jumper Wire.
- Fuse #18 Keeps Blowing.
- Where To Buy The Headlight Switch And Save.
- More Ford 4.6L, 4.8L Tutorials.
You can find this tutorial in Spanish here: Luces De Iluminación Del Tablero No Se Encienden (1997, 1998 F150, F250, y Expedition) (at: autotecnico-online.com).
NOTE: This tutorial complements the following tutorials on testing the headlight switch on the 1997-1998 Ford F150, F250, and Expedition:
- Testing A No Park-Lamps Problem (1997-1998 Ford F150).
- Testing A No Low-Beam Headlights Problem (1997-1998 Ford F150).
No Dash Lights Troubleshooting Basics
The instrument panel (IP) lights are fed power by the #18 (5 A) fuse of the under-dash fuse/relay box (Junction Box Fuse/Relay Panel).
Battery power is only available to fuse #18 (5 A) when the headlight switch is turned to the ‘park-lamps on’ or ‘head-lamps on’ position.
To be a bit more specific, this is how the dimmer switch works when you place the headlight switch in the ‘park-lamps on’ or ‘head-lamps on’ position:
- The headlight switch supplies battery power to the #18 (5 A) fuse of the under-dash fuse/relay box.
- Battery power is fed to fuse #18 across the brown (BRN) wire of the headlight switch's 6-terminal grey connector.
- Once fuse #18 gets battery power, it now feeds it to the dimmer switch via the dark blue with white stripe (DK BLU/WHT) wire of the 6-terminal grey connector.
- The dimmer switch (inside the headlight switch) gets chassis ground from the black (BLK) wire of the 6-terminal black connector.
- Once the dimmer switch gets battery power from the #18 fuse, it now feeds power (at a lower dose) to:
- The instrument panel (IP) illumination lamps across the light blue with red stripe (LT BLU/RED) wire of the headlight switch's 7-terminal grey connector.
- The radio illumination lamps across the light blue with black stripe (LT BLU/BLK) wire of the 6-terminal black connector.
A ‘no dash lights’ problem is usually caused by one of three things:
- Blown fuse.
- Defective dash light dimmer switch.
- Electrical short in the wiring of the dash light circuits.
The most common issue, causing a ‘no dash lights’, is a defective dimmer switch (which is part of the headlight switch assembly).
Another common cause of a ‘no dash lights’ problem, that I've seen a lot, is an installation done incorrectly of an aftermarket component like a radio, gauge, etc.
TEST 1: Making Sure Fuse #18 (5 A) Is Not Blown
We're gonna' start of by making sure that the #18 (5 A) fuse, in the under-dash fuse/relay box, is not blown.
If you have already checked fuse #18 and this bad boy gets blown every time you turn on the headlights, then skip this test step and start at: TEST 3: Bypassing The Instrument Panel Dimmer Switch.
IMPORTANT: Don't use a higher amperage rated fuse instead of the 5 Amp fuse.
NOTE: You can find the descriptions of all of the fuses of the under-dash fuse/relay box here: Under Dash Fuse And Relay Box Diagram (1997-1998 F150, F250, Expedition).
OK, let's get started:
Locate and check fuse #18 (5 A) of the under-dash fuse/relay box (see illustration above).
Fuse #18 feeds battery power to the instrument panel (IP) illumination lamps circuit.
Remove the fuse and visually inspect it. The fuse should not be blown.
Replace the fuse if blown. Use another 5 Amp rated mini-fuse.
Turn on the headlights. If all is OK in the circuit, the fuse should not get blown.
Let's interpret your test results:
CASE 1: Fuse #18 was not blown and does not get blown when the headlight switch is turned ON. This is the correct and expected test result.
The next step is to make sure that the #18 fuse has battery power coming from the dimmer switch inside the headlight switch. Go to: TEST 2: Making Sure Fuse #18 Has Power.
CASE 2: Fuse #18 was blown and gets blown when the headlight switch is turned ON. The next step is to see if the dimmer switch itself has fried internally and is causing the fuse to get blown.
Your next step is to go to: TEST 3: Bypassing The Instrument Panel Dimmer Switch.