electrical problems

[stranman]

I picked up both an M725 and M715 over the last several months.
I seem to be having a similar problem with both.
Blinkers and headlights seem to work intermittently.
Will work fine for a while and then just stop working.
I checked the blinker control switch in the M725 looked very good inside. I swaped the light control toggle switch out of the m715 into the m725, but it did not seem to alter the problem. Is there any common problem with these trucks that I should check 1st? I also could not find any fuses in the truck?

[k8icu]

First you should down load the manuals from this sight. They are very good at trouble shooting issues like this.

Second there are no fuses on a MV but there are a couble of circut breakers.

Some things to check for. Assuming that your truck hasn't been altered by the forest department etc then first check the wires for continuity. If the wire has a break in it, it will be intermittant. Also check condition of the wire. Next check the grounds. Make sure your lights are grounded to the body with the proper washers. Your lights should have an internal/external star type washers between the bolt head and the body of the truck. Lack of ground will do screwy things on these trucks. Then check the turn signals circut is it properly grounded. Again refer to the manuals for help.

Good luck.

[Barrman]

Joe wrote it all. Manuals and CHECK THE GROUND!

MVM magazine had a real good article a month or so ago about the grounding problem. The light buckets that are the front and rear blinkers/park lights/b/0 lights at each end are grounded through the two bolts that mount them to the truck. Each bolt grounds different lights inside the bucket, so having just one of them grounding will only make some of the lights work some of the time. I really mean some of the bulbs. Wire 21 might work the top right bulb when grounded, but not grounded it might light up the bulb for wire 23 this time and the bulb for wire 461 the next time. Really weird stuff happens when the grounds aren't right.

[stranman]

Thanks for the info guys.
I have already downloaded some of the manuals, its a great resource.
A gave the wires a quick look over and did not find anything.
The tip on the grounds is what I was looking for. Both trucks have been altered from original. M725 not too much, rear lights are not original but newer military style. M715 a fire dept got a hold of. Rear lights are non military 12volt, as where front blinkers, I removed non original front blinkers and was reinstalling original type lights, original wires where still in place.

[Barrman]

Mine had the same nicely done conversion by the DSPO fire department.

[randyscycle]

Electricity is lazy. It will find the easiest path to ground, so if there is a ground missing, it will go elsewhere. By chance do any of the other lights glow dimly when this problem occurs? That's a big indicator of a ground issue.

A good thorough look at all the connections, a good thorough look at the manual will get you through this no problem. Electricity isn't a mystery, unless you let the magic smoke out of the circuit......

[stranman]

Headlights will sometimes just flash on for a moment than go off, its almost as if something can not handle the load.
I was never very good with the electrical aspects of automotive tinkering.

[airborne]

The light switch has an internal circuit breaker. Now when I got my truck the F.D. had installed the 'new' lights in it, and had pinched the wires between the housing and frame. They would come on for a couple min's and click off, reset them selfs, come on and then go off again. Maybe something to check. My,.02. Dave.

[brute4c]

Yep...either the wires are pinched and causing a short or something else is overloadig the 3 lever light switches internal circuit breaker and causing it to pop.

I had one switch that was damaged internally enough to where it would allow voltage a path to ground at time and would pop the breaker. So it could be nothing outside he switch is bad...it could be just that the switch is...

[Barrman]

Take a look at your hi beam selector switch. My guess is the selector switch, pinched wires as mentioned already or bad 3 lever as also mentioned.

The hi beam switch has 3 wires. 1 input from the 3 lever and an output for hi or low beam. Unplug all 3 and verify that power is coming in from the 3 lever. If that checks out ok, try a direct connection with a jumper wire to either the hi or low beam circuit. If they both work individually, then it is the selector switch.

You could also just put your hand on it when you turn on the lights and see if it gets hot.