Multi-Meter versus 75 year old truck

Good afternoon to anyone who still uses a multi-meter to troubleshoot vehicle lighting problems. I have a 1945 Dodge pickup, rewired about 25 years ago. a few weeks ago, the low-beam headlights quit working, high beams still ok. so far I find blown fuse at the relay for the low beams. It is chilly out, so I have been slow about troubleshooting this thing.

I may finally check it out more this afternoon. Just looking for interested folks opinion as to what I will find.
BTW, the blown fuse is an AGC-20. Thanks for any comments.

Dennis M. in W. Tenn.
 
(reply to post at 08:5out3:24 01/22/22)

First things I would check are the bulbs themselves . I've had a filament post break and short out the circuit enough to blow one fuse after another until I realised what had happened .
 
(quoted from post at 15:42:12 01/21/22)
I'd check my ground connections too

john


Nothing wrong with checking grounds, especially since that is usually the problem with lights not working. However, When a fuse blows that is usually due to ground where you don't want it, such as insulation wearing through or a component drawing too much current due to wear. A relay can have insulating coating on the winding wires break down resulting in a short circuit.
 
After checking for a short that will
blow a new fuse instantly the next thing
I would do is to have a good look at the
fuse holder to be sure it is clean and
has good tension to hold the fuse
tightly. A poor connection there will
overheat the fuse and cause it to melt
and break the circuit WITHOUT the need
for a short or overload
 
Might check the foot switch. Up here in the north country the road salt eats them from the bottom and the hog and cattle poop from your boots eats them from the top. Had one stick once and turn both high and low beams on. Made for plenty of light for a short while.
 
My old Dodge had similar problem.Ground looks good & tested good from ground to ground for lights.Check to see if you have resistance between the actual wire that is ground,spade lug, & ground. I've had resistance between ground & the wire giving dim lights.Don't go by looks shoot for zero ohms.
 
(quoted from post at 17:23:06 01/21/22) Might check the foot switch. Up here in the north country the road salt eats them from the bottom and the hog and cattle poop from your boots eats them from the top. Had one stick once and turn both high and low beams on. Made for plenty of light for a short while.

Yes! The dimmer switch.
 
So does the low beam relay have it's own fuse. If it does that rules out a bad dimmer switch. If the fuse is before the dimmer switch I certainly would suspect the dimmer switch as was mentioned. You say it was rewired. Did that include new light sockets? The restoration electricals we get today are much less reliable than the originals but i don't know about the quality of the components 25 years ago. A bulb contact in a socket could be cocked and touching the side of the socket. Just another easy thing to check out.
 
DMartin9N=2N,

Multimeter is my choice too. Blowing a fuse is a sign of overload. My guess would be a short. A very lose
and moving ground terminal may also be cause an high amp draw,

Using a circuit braker in place of the fuse, saves money, and will also possibly give you more time the
chase the short. Happy hunting!

Guido.
 
Good evening, posters, I am replying to my own thread. I measured the current at the (empty) fuse clips, it seemed reasonable, so I installed another fuse, problem seems solved.

The low beams worked ok while I went for a half-hour ride, dimmer switch on floor seems ok, so I am calling the problem fixed or at least gone for now.

Thanks for the useful suggestions!

Dennis M. in W. Tenn.
 
(quoted from post at 20:04:10 01/22/22) Good evening, posters, I am replying to my own thread. I measured the current at the (empty) fuse clips, it seemed reasonable, so I installed another fuse, problem seems solved.

The low beams worked ok while I went for a half-hour ride, dimmer switch on floor seems ok, so I am calling the problem fixed or at least gone for now.

Thanks for the useful suggestions!

Dennis M. in W. Tenn.



Good for you and thanks fo posting back! If I were you I would stay within 50 miles of home after dark for a few weeks, LOL.
 

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