TEST 4: Testing The Dimmer Switch's Ground
If you've reached this test step, you have:
- Confirmed that fuse #18 (5 Amp) doesn't get blown (TEST 1).
- Confirmed that fuse #18 has battery power with the headlights on (TEST 2).
- Confirmed that the instrument panel illumination lamps come 'on' when you jumpered terminals 5 and 6 of the grey and black connectors (TEST 3).
In this test step, we're gonna' make sure that headlight switch is getting Ground.
Ground is provided by the black (BLK) wire of the black headlight switch connector. The black (BLK) wire connects to terminal #1 of the connector (see photo above).
Alright, let's get started:
Place your multimeter in Volts mode.
Probe terminal #1 of the BLACK headlight switch connector with the black multimeter test lead.
Probe terminal #5 of the GREY headlight switch connector with the red multimeter test lead.
Terminal #5 (TAN/WHT wire) gets battery power from fuse #7 (15 A) of the under-dash fuse/relay box and is hot all of the time.
Your multimeter should register 10 to 12 Volts DC if the BLK wire has Ground.
Let's take a look at what your test results mean:
CASE 1: The multimeter registered 10 to 12 Volts. This is the correct and expected test result and tells you that Ground is present in the BLK wire.
So, if you have confirmed that:
- Fuse #18 (5 Amp) doesn't get blown (TEST 1).
- Fuse #18 has battery power with the headlights on (TEST 2).
- The instrument panel (IP) illumination lamps come 'on' when you jumpered terminals 5 and 6 of the grey and black connectors (TEST 3).
- Ground is present in the BLK wire of the black connector (TEST 4).
, then you can conclude that the IP illumination lamps dimmer switch (of the headlight switch) is defective. Replace the headlight switch.
CASE 2: The multimeter DID NOT register 10 to 12 Volts. This test result usually indicates that the Ground wire is 'open'. In other words, it's not connected the your pick-up's chassis.
Your next step is to restore Ground to this wire and re-test. Restoring Ground to this wire should get the instrument panel lights going again.
How To Make A 5 Amp Fused Jumper Wire
Using a fused jumper for TEST 3 is the safest way to test the instrument panel illumination lamps circuit.
Making a fused jumper wire is easy. You're gonna' need 2 female vinyl insulated terminals, 2 pieces of wire, and a 5 Amp fuse.
The jumper wire should resemble the fused jumper wire in the illustration above.