Purpose of the fuse on the headlight switch.

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bpoland858
Posts: 57
Joined: Mon Mar 22, 2010 6:16 pm
Location: Baltimore, MD

Purpose of the fuse on the headlight switch.

Post by bpoland858 »

You're reading: Purpose of the fuse on the headlight switch.

While getting my 57 T-Bird ready for a car show on Tuesday, I decided to check my tail lights and brake lights for bightness. To my surprise, I have no tail lights. I checked the headlight switch and found the little fuse was blown. I can see where that may cause the tail lights not to work when the headlight switch is pulled, but I wouldn’t think it shouldn’t affect the brake lights.

What would be the best way to troubleshoot this? Any pointers would be appreciated.

Bill P.

1957 ‘D’ Bird

55Greg&Amy

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Post by 55Greg&Amy »

The 7.5 amp fuse on the headlight switch only powers the courtesy lamp in the dash and the door jamb switches. If this is blown, check the wiring to the map light and door switches for bare wires especially where the wires exit the kick panels and enter the door jamb. The brake lights could be the brake switch on the brake line junction block (round with 2 terminals and threaded in the block) below the master cylinder which happens most often. Try unplugging both wires and hook them together. If you get brake lights, replace the switch with one available at most parts stores locally for about $10.00, very easy and usually don’t loose any fluid while doing this. If no lights, leave the wires hooked together and go to trunk and wiggle wires on and around the bulbs for possible loose ground. Also check the wiring junction block under the dash at the bottom of the steering column where the turn signal wires also plug in for a loose connection. Try jumping a wire from the Green wire to the Green wire with Orange band. Did the taillights work? If not the turn signal switch in the column is bad. If yes remove jumper wire. Do the dash lights work? Make sure to rotate the headlight switch while checking. Does the clock work? If no clock, check the inline fuse (blue wire with black band). Check for power to the fuse with tester and good ground. If you get voltage then the headlight switch is good. If no power, disconnect the battery and take headlight switch out by pulling the shaft out after pushing the small plunger on top center of the switch (the only thing with no wires attached) then unscrew the nut from the front side. With the power still off and switch hanging where you can see it, connect a continuity tester from terminal B (yellow wires) to terminal A (green wire for taillights and blue with black band for clock). If you get continuity the switch is good, if not it means the internal 12amp circuit breaker is faulty, replace headlight switch. Did dash lights work when checked earlier? If yes then switch and rheostat are good. If not, check for continuity between terminal R (black wire) and terminal I (blue wire with red band) while rotating the rheostat. If no continuity, replace switch (or rheostat if you can find one). If good, follow the black wire from the headlight switch to the tail lights. There is a connector somewhere between the headlight switch and the connector that is located in the trunk. (I cannot remember where but should be under the dash). If both connectors have continuity the only other thing that can cause no brake lights is the actual turn signal switch in the steering column. There is nothing else to check as long as both taillight bulbs are good. Lastly, make sure to replace wires to brake switch if not already done. Hope this helps and good luck.

Last edited by 55Greg&Amy on Sat Sep 18, 2010 8:57 am, edited 1 time in total.

Greg Minnich

Fort Wayne, In

bpoland858
Posts: 57
Joined: Mon Mar 22, 2010 6:16 pm
Location: Baltimore, MD

Post by bpoland858 »

Greg,

Here is something strange. if you turn on the headlights, the headlights work fine. The park lights come on if you pull the switch to the first indent. No tail lights in either position. The clock has never worked, since I have had the car (6 months). The map light (courtesy) works even with the blown fuse on the headlight switch.

You have given me some good places to check. I will check the junction block at the base of the steering column. That sounds like it might be a likely spot for the problem. I will also check the brake light switch.

Does the wire for the brake light switch also pass through the same junction block?

Bill P.

1957 ‘D’ Bird

Read more: Headlight Change 1983-1986 Ford F-250 1984 Ford F-250 6.9L V8 Diesel Standard Cab Pickup

55Greg&Amy
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Post by 55Greg&Amy »

Yes the brake lights do go through the same block (green Wire) but the tail lights do not. The brake lights and tail lights are fed by two different wires. If you have neither, then it sounds as if you have a bad ground situation likely in the trunk.

Greg Minnich

Fort Wayne, In

bpoland858
Posts: 57
Joined: Mon Mar 22, 2010 6:16 pm
Location: Baltimore, MD

Post by bpoland858 »

Greg – I just went out and checked the brake light switch. I crossed the two wires and NO brake lights. Can you remember where the ground wire is located for the tail lights. Is there a common lead for the ground for both tail lights? I don’t know why I checked, but I do have turn signals, although the drivers side does not blink, the passengers side does.

The junction block at the base of the steering wheel, is that in the passengers compartment or under the hood? Dumb questions I know.

So, no brake lights even with the wires from the brake light switch connected together. No tail lights at all, and turn signals do work (light up), although the drivers side doesn’t blink.

I have two wires going to each tail light and I am guessing that both of those are positive (one for tail lights and 1 for brake lights).

If there is a common ground, I would guess that it is the body / frame itself.

I wouldn’t this is related but last weekend we replaced the entire fuel system from tank to carb.

Bill P.

1957 ‘D’ Bird

Joe Johnston
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Post by Joe Johnston »

While checking wiring, check to make sure the junction blocks on the innerfenders are wired correctly per the manuals. VERY easy to have them wrong even when looking at the manual as you have to make sure you are looking at them from the right direction.

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55Greg&Amy

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Post by 55Greg&Amy »

The junction block is in the driver compartment just to the right of the column near the dashboard supports. The brake lights are grounded by means of the bulb housing to the tail light housing and the tail light housing to the vehicle body. Dumb question but did you try to replace the bulbs with known good ones? You said that 1 front bulb doesn’t blink. Replace the bulb because another strange thing about these vehicles is that if the opposite corner front turn signal has a bad bulb or poor ground it can affect the rear, RF and LR or LF and RR. If this doesn’t work try the process of checking the turn signal switch that I posted earlier. Keep me posted and we should be able to work through this.

Greg Minnich

Fort Wayne, In

bpoland858
Posts: 57
Joined: Mon Mar 22, 2010 6:16 pm
Location: Baltimore, MD

Post by bpoland858 »

About 3 months ago, a friend of mine pointed me to a treasure trove of manuals for a 57 tbird that a guy was selling on eBay. There were 6 or 7 that included the shop manual, Ford-O-Matic trans, trim manual and the Electrical Manual. Thanks OldMics !

Well at least I have a little indication of what I’m looking at. I was never really versed at reading a schematic diagram but, for those that don’t realize the role that the headlight switch plays , it is the first link in the power supply chain.

Greg, you are correct, It does supply current to the courtesy lights, but even more interesting, it supplys power to the turn signal switch. The turn signal switch distributes power to the wiring harness to the rear of the car for tail lights, turn signals, brake lights and the lowly tag light.

I have not been able to get back out to the car this morning, but it’s looking like either the headlight switch (terminal A, auxilary power) is shot or my turn signal switch ia having issues.

The hunt continues….

Bill P.

1957 ‘D’ Bird

Read more: Headlight Dust Covers Are They Necessary? » Lights Pick

55Greg&Amy
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Joined: Sun Nov 09, 2008 8:43 am

Post by 55Greg&Amy »

Very interesting on how yours is wired. My schematic shows the turn signals hooked to the R terminal and the brake lights hooked to the A terminal of the headlight switch which both use an internal 12amp circuit breaker and the Courtesy light and Door jamb switches (both wires being Green w/Yellow band) being the only ones hooked to the fuse. Maybe someone previous had the light switch wired incorrectly. I just had a friends 57 in my garage this past Friday and replaced his fuse as well as repaired the broken wires in the door jamb switch which had shorted out the fuse. His brake lights and tail lights were working fine even before replacing the fuse. If your brakes are hooked to the fuse 7.5 amp they will pull too much current and blow that fuse. They should be on the 12 amp breaker that self resets. I use a wiring schematic that is 14″x34″ that I obtained from CASCO at www.classictbird.com part numbers WS57 and WS57DM (depends on whether you have the dial-o-matic seat or not) each only $11.00. Much larger than the ones in the shop books that are nearly impossible to read.

Greg Minnich

Fort Wayne, In

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Post by redstangbob »

I’d be interested in a comparison of Bill’s and Gregs’s schematics. I’ve found 3 mistakes in the 65 schematics that I have, two from Osborn and one from TBHQ. Tracing things down is hard enough without the book sending you on a wild goose chase. JMO Bob C

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bpoland858
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Post by bpoland858 »

I ended up enlisting the help of a friend that is very versed in Early Birds. Thank You OldMics ! I don’t think I could have pulled this off as quicly as you did, if at all.

The final report card:

2 broken wires under the dash (tail lights), 2 blown lights, 1 park light installed backwards Purpose of the fuse on the headlight switch. (How in the Hell do you do that?) and lastly, 1 bad brake light switch.

I don’t know how long it has been this way, but it’s fixed now.

Bill P.

1957 ‘D’ Bird

55Greg&Amy

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Post by 55Greg&Amy »

Glad its fixed and that is all that matters. Now on to the next thing that will go wrong with an old car. FUN FUN FUN.

Greg Minnich

Fort Wayne, In

Lou
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Interior lights

Post by Lou »

I have a unique situation on my 56, when the headlight switch is pulled out all lights work fine and the rheostat works on the instrument panel. When I turn on the ignition, it takes over the instrument panel, they are lit all the time, even with the headlights off and the rheostat doesn’t work while the ignition is on. Anybody have any ideas as to the problem?

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Category: Headlights