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Driving around a few days ago I blew my dash/tail fuse. Popped a new one in, got 30 miles out of it then it blew again. Now it blows them as soon as I pull the headlight switch.
I just removed the switch and the rheostat looks like it melted apart. Circled in red. This is an original Delco-Remy switch. You guys think this is the issue, or just a result of another issue?
The switch looks a whole lot less than great. But what came first? Did the switch melt because of a short somewhere else? Or is the switch the source?
do you run relays on your headlights to protect your ageing switches?
If not, consider installing them.
In the short run. I would hot wire around the switch and see if dash lights or tail lights blew fuses. Obviously I would wire in one at a time to test.
On a 40 -50 year old car. A short could be anywhere.
That's exactly what I was concerned about. I'd prefer not to install a new switch only for it to melt as a result of the short being somewhere else. Good call on the idea to test one portion at a time. If I hotwire and neither blows a fuse, then the switch would be the culprit, correct?
With the headlight switch pulled from the connector check to see if the ORANGE wire is going to ground.
The orange wire "TAIL" fuse is what powers that portion of the headlight switch.
"IF" no then check if you have continuity between the rheostat and the metal body of the headlight switch.
The metal body of the switch IS grounded and that provides the ground for your courtesy lights when **** is turned full CCW.
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You have to trace the power. I had a melted wire in the fuse block. You have to remove it to see the issue. You will have to get a new switch then see where the power is going. You can also start probing wires for a short as well.
So I tested all the connections in the plug using the courtesy light ground (white wire also in the plug) and all tested out to have 10ish ohms on the 200 ohm setting. Was that a good ground to use, or does that tell us nothing because it's a different circuit? I think I'll go back and test circuits using the speedometer contact as the ground which is what the headlight switch actually grounds to.
I will note that the ground strap was pretty crusty when I first went out to test today. The probe had a hard time getting continuity. I removed the strap and cleaned it/reinstalled and then took this pic.
So after cleaning the ground strap and installing a new Lectric Limited headlight switch (thanks @08Indy ), the lights are functional and the fuse is not blowing! HOWEVER. I have a new issue that's super odd.
With the car off, the headlights and high beams function through the switch, all the gauge lights come on and everything is solid.
When the car is running and alternator is spinning, everything is okay UNTIL the high beams come on. They function for about 5 seconds, then everything - High beams, gauge lights, radio, all flicker, and the ammeter goes nuts. Regular headlights do not cause this issue. Also when the car is running with the alternator disconnected, the high beams do not flicker.
Has anyone experienced this before? This was sudden, as the high beams did not cause a problem before my oem headlight switch crapped out.
Reading up it seems like any new replacement switch you purchase comes with an inferior circuit breaker inside it, which causes my high beams to flicker when the breaker flips. I guess the high beams are enough current to cause it to overheat but the headlights are not. So my options seem like either switching to a relay setup or pulling the rheostat out of the new switch and installing it into the old switch. I'll likely go with the former to avoid breaking the rheostat.
I'm back to functional headlights and no blown dash fuses! I installed headlight relays and wired them to the power and ground off the alternator, since there's no horn relay on a 75 like most instructions tell you to utilize.
Here's my complete timeline in case someone else comes across any of these issues.
1. Gauge cluster and tail lamp fuse started blowing when dash lights were switched on. Headlights and high beams were fine.
2. Replaced fuses, which began to blow immediately.
3. Removed and inspected Delco switch, it appeared to have a compromised rheostat.
4. Installed Lectric Limited switch. Gauge cluster and tail light fuses did not blow, good! But with car running and high beams on, the high beams flickered. Not good.
5. Installed headlight relays to take the load off the headlight switch. Now everything functions properly, no flickering.
So my suspicion is that the Delco switch probably had a bad rheostat while the headlight switch portion is still good, while the Lectric Limited switch has a good rheostat but an inferior thermal cutoff switch for the headlight load. Could be bad grounds as well, maybe.
Hope this can help someone else! I'll get a pic of my relay positioning this weekend.
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Dash/Tail light circuit blowing fuses
