Horn switch problem?

[sibot]

Hi,

Just had Bongo in for an MOT/Service, knew horn wasn't working when it went in. Garage rectified to pass MOT by fitting a dashboard switch into a live feed for the horn, but it looks ugly and isn't fused as far as i can tell. Also bypasses the relay.

I've been trying to find out where the problem is, using past threads in here, but i'm a bit stumped. What i've done so far:

Horn itself works when using the newly fitted switched Live.
Checked Fuse 5 - fine.
Pulled relay and swapped for another, still no horn.
Checked relay socket contacts: 2 right hand contacts are live, but have very low voltage measured (below 1V). Lower left contact is not live, but has low Ohm resistance (horn feed?). Upper left contact measures OC resistance, with and without horn button pressed.

Garage indicated the problem was 'no power to the steering wheel button' - but surely if it's a switched earth there wouldn't be power here anyway normally? I have an SRS Airbag wheel so don't really want to be taking the steering wheel apart.

Any advice on next steps to trace the problem would be appreciated - I have a multimeter but only one pair of hands. I don't know if it makes a difference, but it appears to be a two-tab horn that's fitted, so not an original.

[jaylee]

Do you have an airbag on the steering wheel....?

Just a thought.. you could try using the meter to run from the constant live feed at the horn relay connection, (with the relay removed.) then test the voltage at the earth switch point on the relay connection when the wheel horn is pressed...? It maybe a duff connection at the negative trigger to the chassis through the steering at the wheel button..???

[sibot]

Thanks Jaylee, I do have an airbag on the steering wheel.

Reading again what I wrote, and thinking about it logically, surely the live connection at the relay should be at +12V to earth, since that's what I read at the fuse box, and so the problem is a break in the live feed to the relay on the yellow/red wire since it's measuring <1V?

Not sure how to go about tracing a break though, 95% of that cable length is inside the black plastic tubing which looks like a complete pain to open up then tape up again.

[jaylee]

I would wager any break would not be in the "thick loom?" running through the bulkhead... Try the connection to the relay connector... (Is it not a crimped female spade in the relay connection housing?) It may be frayed there??

Can you hear the relay clicking..?

This diagram in the wheel with air bag may help? http://lushprojects.com/bongopartsmk2/c ... 02.html#14

This may help too? http://www.g8dhe.net/bwm/bwmanualp.htm?1995/Page_78

Another old topic that may help..? Be careful!!! http://www.igmaynard.co.uk/bongo/forum/ ... x+the+horn

[jaylee]

OK, thinking about this again.... Looks like two constant 12v live feeds to the relay from the same source... They split off, one ongoing through the switch in the relay to the horn, the other powers the coil in the relay to switch the feed to the horn.. Yer coil may not be getting the charge..?

Without being there i wouldn't know where the garage wired it from, regarding the new fix..

You haven't had any work done at the back of the fuse box in the cab perchance..? Say some LB wiring??

[sibot]

Cheers,

Yes there is some LB wiring, and a lot of insulating tape about under the dash but I couldn't see anything near the y/r wire from the horn fuse before it disappears into the loom.

I'll start at the relay end and try to work back, as you say i think where the wire splits is a likely candidate.

The new horn switched live is just run directly from the battery terminal, through a sprung push button switch on the dash and down to the horn. Jury rigged to pass the MOT. He suggested I took it to someone else to be made good, but having already spent the thick end of £600 I thought it was probably worth having a look myself. Worst case I put 12V across myself .

[jaylee]

Yes there is some LB wiring, and a lot of insulating tape about under the dash but I couldn't see anything near the y/r wire from the horn fuse before it disappears into the loom.

Have another looksee in that area...? Especially directly behind the fuse box..?? Ya never know...! I've seen a few "rats nests" behind there, with wires going absolutely nowhere...

[sibot]

Ok, found the main problem - the y/r wire to the relay connector had been spliced in the past, at the relay end before it joins the main loom, and the splice had corroded to the point that I had to take about 1" off the splice wire to get to clean wire. Cut back all the wires and rejoined, now have 12V to the relay connector.

Next issue seems to be that only one of the steering wheel horn buttons works. One button sounds the horn just fine, the other does nothing. Is it worth trying to sort this out tomorrow, or best just to leave well alone since it's technically working? (I removed the jury rigged wiring and extra button).

[jaylee]

Not having the air bag wheel my self, i would be advising on uncertain territory...

But since yer on a roll you could try looking first under the steering cowl.. On part 66-CS0 there appears to be a loom of what looks like the airbag gubbins, & possibly the earth from the relay to the horn switches on the wheel?? (The separate smaller what looks like a 2 pin connector in the loom?) which could be a 2 wire earth feed going to each separate horn switches that then earth through the column??? http://lushprojects.com/bongopartsmk2/c ... 02.html#14

Just a wild guess before taking the airbag assembly apart...!!??

[sibot]

Had a furtle about and everything looks fine as far as I can tell without taking the rest of the covers off the wheel and steering column. There is some movement of the wheel covering around the non-working switch, so I'm wondering if it's been disturbed when the garage were trying to work out what was wrong and something has been knocked loose.

I'm thinking of changing the habitation electrics over to the LB in the next few weeks (they are all still on SB, only the fridge and new gubbins were wired into the LB on conversion), so I might pop the wheel covers off when the battery is disconnected for that and see if there's anything obvious.

[jaylee]

Good idea Sibot. There is a chance that the defective horn button may not be making contact & going to ground..
I dare say the garage may have prised the centre cover/airbag unit loose & the assembly for the button behind, then "chicken'd out" for fear of causing more trouble with the airbag assembly..? You don't want defective flashing bag light/blown safety bags @ MOT time!

I'm confident you can get it all working.. Let us know how you got on..

[sibot]

Well, had the top module off the steering wheel and it turns out that when the garage had re-assembled it after trying to find out why it wasn't working they had neglected to connect the switch wire back to the contact. Plugged it back in and horn now works from both buttons on the wheel . Thanks for all your help.

[jaylee]

What a brilliant result..!

... It does make me wonder about the ability of some of these garages though..