I suspect the issue I'm asking about is simply one of inspecting wiring and correcting a short, but thought I'd ask the HAMB braintrust just in case this is something one of y'all has encountered and fixed. The gremlin: In my shoebox (aka 50Fraud), when I go over even a fairly minor pothole or manhole cover in the road, the headlight fuse will blow. On smooth pavement, the lights will stay on an run indefinitely. Here's what I know: The car was rewired when originally built in the mid-late 90's. It's still running a '50 Ford headlight switch, and currently has '52 Ford headlights with halogen bulbs running on relays that have tested good on a relay tester. Taillights are stock '50 Ford units with bayonet-mount LED bulbs (a concession to safety as incandescent bulbs are very hard to see)that have also tested good. Turn signals remain functional when headlight fuse is out or blown. The questions: Any known spots where wiring is vulnerable on a shoebox, like passing through a particular joint or panel? Is the headlight switch known to be problematic? Any general tips on troubleshooting wiring? Thanks in advance!
Is it only the headlights that go out, or do you lose all of them? If it's just the headlights, look at the wiring to/from the headlight relays.
a few questions; What does the headlight fuse protect? The signal circuit from the switch thru the hi/lo switch to the relays OR the feed to the relays? What is the hi/lo switch? Old school floor stomp switch or a turn signal stalk pull? Where are the relays? My first guess is that whatever circuit is shorting out over a bump against ground is probably at the hi/lo wiring on the floor, but that depends on the fuse and switch. Other possibles are along the inner fender and up to the relays, wherever they are located. This is all if the control circuit is fused. If the relay feed is fused, it's going to be those new wires and out to the headlights. The area mentioned by @BJR right at the buckets is a good first place to check. This is where you perform what is called a 'wiggle' test. Turn on the lights and start grabbing a section of the suspect wiring and wiggle it like it would going over a bump. Keep trying to isolate the section that causes the problem.
There's no foot switch in the car anymore. There is a toggle under the dash, but it does nothing I can find. There may not be a highbeam selector wired at all right now. Relays are mounted on radiator support behind the grill. Wiring to them looks sound but will take another look when out in the garage and/or I get the car in the air.
Headlight and "regular" taillights. Brakelights and turn signals remain so just limited to that circuit. Relays and wiring look good, but will reinspect when car is up in the air.
Blowing a fuse is not going to happen where the wiring is up in the air, only where it can bounce on metal ground. With the tail lights also being affected, it is fused to the switch and control circuit, not the relays. So the wiring from fuse box to switch, from switch to relays. The stuff from the switch forward should be checked carefully since it's either new or the old stuff cut and spliced to bypass the hi/lo switch.
In that case look at your light switch and/or dimmer switch. Brake and turns are on separate circuits. If it has an OEM style switch that's been replaced with an aftermarket one, those are junk.
I fully agree with your point, and I should have maybe been more clear with my response: the car is so low that I have to get it in the air to inspect wiring from the headlights - which may be moot since the wiring between the fuse panel and switch is all under the dash as far as I can tell. I appreciate the tips and specifics!
While I would strongly suggest that all the wiring should be looked at, the wiring from the relays to the headlights are not suspect right now. It's the control circuit from the fuse to the switch and from the switch to the relays. Since the floor switch is bypassed, the wiring probably goes from the switch thru the firewall and along the inner fender to the relays. The hole in the firewall is a strong suspect. Reach under the dash and wiggle the wiring at the switch with the lights on. Also wiggle the wiring near the relays. This can be done with a door and the hood open, no jacking. EDIT: it sounds like the wiring was not done to OE standards, look for any bare wire up under the dash while you are there.
Your car wouldn’t have originally had a relay for the lights. It’d be worth checking where the fuse is in relation to the relay, is it in the power feed to the relay or the signal feed to the relay from the switch. You can then at least narrow down which bit of the wiring to look at.
@Oneball Judging from his reply, I'd say it's the signal feed. I can't see the relays being used to power the tail lights along with the headlights. Crazier things have happened, though.
I can't****ist other than to recommend you avoid driving in Washington state. Aside from the highest gas prices in the US we have some of the roughest roads, highways and freeways in the nation. It will be a dark drive for your car until find and solve your issue.
I had a marker light once that had lost it's glass bulb shell somehow and blew, but under a certain set of circumstances a piece of filament would hit the metal housing and blow a fuse.
I recommend one of these, it's a buzzer/circuit breaker. You put it in place of the fuse and it buzzes when shorted and then resets. The Blue one has a buzzer and the Red one doesn't. https://www.amazon.com/dp/B000RFOP1I/?tag=atomicindus08-20 After it's hooked up start wiggling and tapping everything (relays and switches included). Sometimes the switch can short, so jiggle the stem when the lights are on.
The Jalopy Journal
