Blowing headlight fuses and can't figure out why

[2TonCommon]

I'm wondering if anyone else has run into this issue.....
Tractor: Mahindra 2816 HST
Model year: 2010
Hours: 207
Problem: 15 AMP mini-fuse blows when switching the headlamps from HIGH beam to LOW beam.

I've done a fair amount of investigating in the lighting circuit looking for skinned wires or chafed wires that might have cut through the insulation but did not find any.
With the headlight plug connectors removed (both R and L) from the back of each bulb and putting a multimeter in DC volt mode on the hot connector leads (three spade terminals), as soon as I try to read voltage on the meter, it pops the fuse.
I've had the main instrument and switch console off and have metered both the HIGH-LOW switch and the multi-function lighting switch from the back bud didn't find any issues.
This has all the indications of a dead short with a hot lead going to ground as soon as the LOW beam switch is engaged.

This only happens when the headlights are attempting to be used in LOW beam mode. All other electrical lights and circuits seem to be working just fine.

I'm trying to avoid tearing into the wiring looms on a grand scale, so if anyone else had seen or heard of this problem, if you could please pass along what you know, I'd genuinely appreciate it. Thanks!

 

[Black Max]

Sounds like a nightmare... You have isolated the switch and bulb itself as being ok, I would unplug your switch on one end, bulb on other end, and switch your meter to ohms or omega sign. Test for continuity to ground on the harness itself( from hot 12v low beam wire with power off) this will narrow down the problem to harness only. Then start looking at the wiring more closely, I assume the bulb sockets themselves look and test good ?

 

[2TonCommon]

Black MAX: Thank you for your input! I'll give your suggestions a try and see if I get any closer to a fix. Much appreciated!

 

[Black Max]

No problem, when using ohms for testing it saves on fuses... Unless you get lucky and see where the spark comes from... Lol. Make sure the power is off, you can disconnect the positive of your battery for safety but leave the negative. We'll get it fixed, too bad I'm here and your there. You will be testing the harness to ground, any thing that plugs in to that particular harness that can be unplugged to further isolate the wiring will help. We need to prove it's in the harness and not a device plugged in to it first. I have seen a simple shorted bulb cause this but you blew a fuse with them unplugged so... I'll look for your info as you find it and please post.

 

[boggen]

TractorData.com Mahindra 2816 tractor information
tractor data does not show a optional cab for your model. so that makes things a bit easier.

you may have a wire harness connector inside the front dash (under the steering wheel),
and then you may have another wire harness just on the opposite side of the firewall. between engine and the dash, though this wiring harness might be tucked away under the floor mat or like and a bit hard to get to.

if you can get to the wire harness plugs / connectors and disconnect them. you could test portions of the wire harness to see what is going on. to reduce amount of wire harness you need to check.

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a wiring diagram for tractor would give info of how many wire harness plugs there are, and shop/service manual would show better locations of were the wire harnesses are actually located.
you might try contacting a local dealer for a wiring diagram to be email/fax'ed to ya, so you can identify wires via "color code" to make things easier to trace.

 

[outlawsix]

Any updates on the cause of your issues? Reason i ask is I have a 2615 HST that my water temp doesnt work but when i turn headlight switch on it pegs out the water temp needle indicating a short. So if you can isolate your short, it may in turn help me. I have went all over the thing with my multi meter with no luck.

 

[r8nger]

Sounds like the short is in the gauge lighting circuit , since it effects the gauge with the lights on. Probably internally .

 

[CobyRupert]

I've done a fair amount of investigating in the lighting circuit looking for skinned wires or chafed wires that might have cut through the insulation but did not find any.
With the headlight plug connectors removed (both R and L) from the back of each bulb and putting a multimeter in DC volt mode on the hot connector leads (three spade terminals), as soon as I try to read voltage on the meter, it pops the fuse.

I assume the bulb sockets themselves look and test good ?

What do you mean it pops the fuse as soon as you try to meter it? It sounds like if you didn't touch it with the bulbs unplugged, the fuse would not blow? If so, check for a bad socket that grounds when you disturb it?