Odd Headlight/Dashlight question
Fleet Mechanic
Joined: Sep 2016
Posts: 1,459
Likes: 70
From: Southern Maryland
Power comes from the light switch down to the fuse block and then directly to the gauge lights. You can't plug them into anything else unless you butcher the wires under the dash. With the lights on, verify you have 12 volts on both sides of the fuse. If no, replace the fuse. If yes, pull the gauge cluster and verify there is a ground connection from the gauge panel to the frame. If yes, check from a known good 12 volt source to verify the ground is good at the frame. There is a yellow wire with a female bullet connector extending form the harness attached to the back of the ignition switch. This is hot at all times. Check from there to the dash support where the ground should be attached that goes to the gauge cluster to verify you read 12 volts. If no, then you need to add a ground strap between the engine and firewall.
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Elder User
Joined: Feb 2019
Posts: 548
Likes: 1
From: NC
Thanks for the really detailed explanation 66v8baby, I'll start testing some places tonight. I did see one nicked wire under the dash last night, but all of it looked in decent shape and as if it were all stock wiring, so that should hopefully make it easier to track the issue down. Thanks again
Fleet Mechanic
Joined: Sep 2016
Posts: 1,459
Likes: 70
From: Southern Maryland
Thanks for the really detailed explanation 66v8baby, I'll start testing some places tonight. I did see one nicked wire under the dash last night, but all of it looked in decent shape and as if it were all stock wiring, so that should hopefully make it easier to track the issue down. Thanks again
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Elder User
Joined: Feb 2019
Posts: 548
Likes: 1
From: NC
Perfect, sounds good. Thanks for that. I'm hoping to find the time from my 9000 mph doberman puppy sometime tonight to check it out, but if not, hopefully by tomorrow. I'll definitely post back here with what I find and what the solution was (assuming I do get to fixing it)
Fleet Mechanic
Joined: Jan 2014
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...going back to your original symptom, that is, no dash lights are present unless the high beam headlights are switched on. It seems to me that somehow the dash indicator light feed is getting power from the same circuit as the high beam filament. Seems like looking at a circuit diagram, wiring colors, and crawling under the dash to discover why should be direct to the point.
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Elder User
Joined: Feb 2019
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From: NC
When looking at the wiring diagram, it appears there is only 1 wire running to the dash lights - the blue/red wire. And then if course the 2 grounds there.
Are there other wires associated with it that I should be looking at that I am overlooking in the diagram? And if I'm looking at this properly, the only fuse associated with that circuit is the same one that controls the brake lights? Being that power is getting to them on high beam but not low beam, makes me lead to believe that the blue/red is fine. I notice there are 2 grounds, does 1 of these grounds work for high and 1 for low beam? I still need to get out there for testing
Are there other wires associated with it that I should be looking at that I am overlooking in the diagram? And if I'm looking at this properly, the only fuse associated with that circuit is the same one that controls the brake lights? Being that power is getting to them on high beam but not low beam, makes me lead to believe that the blue/red is fine. I notice there are 2 grounds, does 1 of these grounds work for high and 1 for low beam? I still need to get out there for testing
Fleet Mechanic
Joined: Sep 2016
Posts: 1,459
Likes: 70
From: Southern Maryland
Yes, the blue/red wire is the only wire going to the dash lights. That circuit has its own circuit breaker, a tiny 2A breaker. On my Custom Cab there is only 1 ground for the dash lights and a second ground for the lights on the auxiliary gauges. The lack of a ground can cause a different circuit to back feed, so you should not assume the regular dash light circuit is good all the way to ground. You could also have 2 wires shorted together. This is most likely to happen at the switch or at the connector to the switch.
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Elder User
Joined: Feb 2019
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From: NC
Finally had time to look this morning, and I'm having trouble chasing down the blue/red wires and ground due to paint overspray. I believe I know which they are, but wanted to double check. Are the ones I have circled in red the two blue/red connections and the ones in the black the 2 grounds?
I found this behind the cluster, what's this go to? I didnt see a loose male connector sitting back there for it and not seeing it on the wire diagram anywhere. Just one wire goes into it, appears to be grey/red.
Fleet Mechanic
Joined: Sep 2016
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From: Southern Maryland
No, those are the fuel (left) and temp (right) gauges. The lights are in the lower corners and the lower of the 2 in the center top. I have a pigtail like that where I can add circuits. Check to see if it's switched or hot at all times.
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Elder User
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From: NC
I'll check the connector out and see what happens. So the blue/red is the wire that runs directly to the bulbs? Dont know why I expected it to go somewhere else.
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Elder User
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From: NC
Does the same wire deliver power to the gauges whether in low beam or high beam? It appears so from the diagram.
The small fuse in the panel has power both in high and low beam (which I believe is where the blue/red connects to). Should that voltage change there as I turn the rheostat?
Where would i check for ground at to see if theres an issue there?
The small fuse in the panel has power both in high and low beam (which I believe is where the blue/red connects to). Should that voltage change there as I turn the rheostat?
Where would i check for ground at to see if theres an issue there?
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Elder User
Joined: Feb 2019
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From: NC
Got my issue figured out. First off, I thought rheostat all the way to the right was full, but apparently to the left is full. That was one issue. Lights were still extremely dim.
Ran a jumper from the back of the panel to the steering column, and lights instantly got brighter to where I could see them. Turns out it was a ground issue, now need to figure out the best way to attach one.
Ran a jumper from the back of the panel to the steering column, and lights instantly got brighter to where I could see them. Turns out it was a ground issue, now need to figure out the best way to attach one.
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