Dim dash lights/headlight swicth

[jdl71]

I don’t expect the dash lights to be like modern stuff but I would think it would be obvious they are on, and unless it’s pitch black it’s hard to tell. I’ve read about replacing the bulbs with led’s but I’d rather not do that. I’m suspecting the headlight swicth is the issue. I’m only getting about 9.5-10v at the panel lamp fuse when I turn it on and rotate to full bright. If I run a jumper from the spotlight fuse and give them a full 12v I can clearly see they’re on and would be happy with that level of brightness. My question is, is this “normal”, as in there is built in resistance in the switch to keep the dash lamps from getting a full 12v, or as I’m thinking, the old swicth just isn’t working as it should?

[AJC]

What is your alternator putting out? Also ohm your switch. The rheostat in the switch should be around 0 ohms at full brightness.

[jdl71]

I was testing with the engine off. Ohming the swicth was going to be next step but wasn’t sure what it should be. Thanks

[damnyankee36]

Another way to check this is to jump the headlight switch at the red and dark green terminals. That bypasses the switch and sends full voltage to the dash lights. You can do this with the connector attached or disconnected from the switch. Actually, any voltage source connected to the green wire will accomplish the same thing.

[jdl71]

Originally Posted by damnyankee36

Another way to check this is to jump the headlight switch at the red and dark green terminals. That bypasses the switch and sends full voltage to the dash lights. You can do this with the connector attached or disconnected from the switch. Actually, any voltage source connected to the green wire will accomplish the same thing.

I pulled the dash light fuse and ran a jumper from the spotlight term and the lights got much brighter. The spotlight term had 12.3v or so.

[AJC]

I would also start checking your grounds. My interior lights were dim on my truck because it was missing the engine to cab ground. You still running the factory ammeter? I have to check if these trucks run a shunt or full power through the ammeter.

[jdl71]

Originally Posted by AJC

I would also start checking your grounds. My interior lights were dim on my truck because it was missing the engine to cab ground. You still running the factory ammeter? I have to check if these trucks run a shunt or full power through the ammeter.

I’ve read that too. But since taking power from another source in the fuse panel makes them brighter, doesn’t that pretty much rule out everything except the switch?

[damnyankee36]

If applying full voltage to the fuse and the lights brighten then his ground is good.

It sure sounds like the switch. When you applied voltage to the fuse that's sending power through the gray wire directly to the lights. The other wire at this fuse is the green wire which goes to the switch.

But just to be sure if you apply voltage to the green wire at the switch that tests the entire circuit after the switch.

[damnyankee36]

I wonder if the switch is not allowing the rheostat to completely turn all the way to full brightness. Can you turn on the dome light using the switch?

[jdl71]

Originally Posted by damnyankee36

But just to be sure if you apply voltage to the green wire at the switch that tests the entire circuit after the switch.

I had considered that there could be a resistance between the swicth and fuse panel but not tested yet. I guess my main question was shouldn’t the switch be passing full B+ to the fuse and it appears it should. That tells me where to look. Thanks.