Mercedes 190 2.6 Wiring Question

[niva441]

Hello All

I was dubious about the aftermarket alarm that came with the 190 when I first used it and thought at some point it would become a liability and would need to be removed at some point before it became a problem. It decided to bring the job forward at 11 the other night.

I'm working my way through the alarm wiring which has been made more interesting as it replaced the system originally fitted by the dealer. So it didn't fit the one bit of paperwork I had, many wires have multiple colour changes with wires cut and soldered onto them. I've traced the wiring into the back left corner of the engine bay (beside the battery) and managed to work out most of the breaks into the original loom from the wiring diagrams. However the following doesn't make sense for an alarm/immobiliser on any of the wiring diagrams I've found (my best guess in brackets):

Purple (or violet) with Black trace (apparently Fusebox to combination switch).

I also seem to have the these wires apparently not coming anywhere, but earthed (they may be part of the original alarm installation):

Yellow (Fusebox to Combination Switch)
Red / White (Fuel Pump Relay to Fuel Pump)
Black

I've worked through the Haynes manual and online but not found an answer to this. I've also looked online for the alarm instructions (Autowatch 346 RLi) and found other Autowatch models, but not this one.

Thanks in advance for any help.

Todd

[niva441]

Turns out procrastination, or as I like to consider it contemplation, isn’t totally worthless. Feeling brave earlier I traced the Purple black wire deeper into the engine bay. It turns it, and the random Yellow/Red wire, are what are breaking the Violet feed to the starter. Undoing the mess is making a lot more sense now. All I now need to do is work out why it is tapping into (but not breaking) the black/blue/green wire from the fusebox.

[PositronicRay]

That's the best way, surprisingly I work out loads of stuff while dog walking.

[jet_noise]

On the "tapping into" theme. I'm assuming the wire is permanently live.

Part of a voltage drop type check.
i.e. if something starts drawing current when it shouldn't there will be a volt drop between a near-battery tap/wire/feed and a tap some way away. Alarm sounds.

Part of a wire-cut detect.
i.e. if the feed to the combo switch is cut the alarm uses its internal battery to sound the alarm.

[niva441]

Tried walking the dogs, but it didn't work this time. The older one doesn't understand electrics and the younger one only does CAN bus systems.

When the alarm started messing around the other night and I decided to remove the alarm unit my next thought was that the siren would trigger. Fortunately (possibly because it wasn't actually turn on) the siren didn't sound. So from that point on the only use the alarm had was to complete the immobilised circuit. Not immediately needing the car gave me space to breath and apart from the starter and one other circuit (diagnostic feed according to the wiring diagram) all the other loom connections were made by stripping the wire and soldering the alarm wire onto them. So yesterday I went for it and unpicked all the alarm connections and took the opportunity to repair some of the bodged repairs that I assume were related to the original alarm installation.

It was quite a relief at the end of yesterday when I reconnected the battery and the starter fired the engine into life. Once I've removed the connections to the electric window switches I'll have to do a full electrical systems check to make sure everything is a complete as I think it is.

Having removed remnants of two alarm installations I now have a large collection of spare wire, this has got to be the only car that will have lost weight after I finished working on it.