56 M170 headlights not working

[iwojimavet]

Both headlights went out at same time while driving. All other lights (convoy/blackout) still work. I pulled the light switch box out, cleaned the connections and screwed it on back tight. Still no go. I got the wiring diagram and know where to look, but I am afraid I,m a novice electrician and don’t know how to check th grounds and the connections. Do I just turn the battery switch on and the headlight switch and hold the meter positive to the ends? Sorry, I have no clue.

[wesk]

It would take 10 paragraphs or so to guide you through a safe troubleshooting effort here. This is where you do some U-Tube research on how to use a VOM, how to troubleshoot electrical circuits and how to inspect and repair bad grounds. Get some of that under your belt first then post for some local help from a restorer in your neighborhood.

I am not trying to avoid your request. I am trying to avoid leading you into a mishap and a lot of smoking wires. 24 Volts will burn up wiring twice as fast as 12 volts will.

When you said you

I pulled the light switch box out, cleaned the connections and screwed it on back tight.

Did you actually remove this?



And opened it up and cleaned the contacts?



or did you just unscrew the plug, clean the pins and screw the plug back on?

Which switch do you have. One of the three above?

[iwojimavet]

Thanks for the info, and will do. I just cleaned off the pins. I'll take it apart and clean the contacts. Thanks for the help. After reviewing Youtube, I'm sure I'll come back for more questions. I see where the headlight wires meet up, just don't know how to test them at that point.

[iwojimavet]

My lightswitch is the late model on the right

[wesk]

They are sealed, non-repairable, throw-aways. No parts or instructions are available for them. The two Bendix models are repairable, rebuildable and instructions are in TM 9-1825E (the excerpts are on our downloads pages).

The best way to trouble shoot these switches is with a test pigtail. You find an old cannon plug that matches the pin size, arrangement and attach wires to each pin that the original plug has wires on. You do this by studying the Pinout Illustration in TM 9-1825E.





I would go one step further and build a small breakout box with a test lamp for each circuit and a long enough harness to reach behind the dash, unscrew the cannon plug and screw my test set plug on and lay the breakout box on the driver's seat. Then apply 24V to wire #15 Pin Letter F. Now just place switch lever in each position and observe that correct circuits are powered up.

In a motor pool the switch being a common stock item they would simply unscrew the plug from the old switch and screw it on the new switch and check vehicle lamps for proper ops. Great if you have a few new in the box switches to do that.

[Stiknruddr]

Fyi if you are running 12v and have the later 3 lever switch it’s probably got a 20 amp circuit breaker inside. I removed it jumpered it put a in line CB. Also ran a 12 ga dedicated power power wire to the switch input. My headlights were suddenly going off like yours.

[wesk]

That's a good point to bring up. trigger's several questions.

1 - Is you jeeps 24 volt electrical system stock & in tact?

2 - These Bendix switches were discontinued mid production on the M38. The M38A1 & M170 never had them but they will function in your jeep but will need an external circuit breaker or fuse. The Bendix switches will function just fine using 12V or 24V input on wire #15 so long as all your lamps match the input voltage used.

As you can see looking at your current switch it was never meant to be disassembled/opened up. Attempts to open them up do not always go well.

[reddog]

check the high beam switch

[wesk]

Another good point however checking the switch requires some knowledge of VOM useage and wiring, all of which we are still working on here.