P38A interior light

Grrrrrr said:

Hi all,

my LHS (near side) interior light hasn't worked in ages. I did have a play a few years ago but then it dropped down my priority list. Today I decided to have a fiddle. Marty very kindly sent me this:

"The interior lights are all driven off the same circuit in the BECM, and then they split on the power board to various connectors to output the light units themselves.

The nearside/rear comes off of C1291, and is supplied a constant 12v from F15 on pin 6 (purple wire), and then it is controlled on the ground side off of the Purple/Red wire on pin 9 of the same connector.

If you pull the light unit out, then it's got a 3 pin connector on it, with pin 1 being the main 12V, pin 2 being the control line from the BECM, and pin 3 being connected to ground. With the interior light on, you should see 12V between pins 1 & 2 at the light. If you do, then chances are the switch or contacts in the switch are dirty/faulty.

If you don't get power or ground control from the BECM when the lights are on, then it could be a wiring issue between the light and the BECM, or possibly in the BECM itself... though there isn't a lot of power going through the wiring, so I wouldn't expect it to damage much internally... I've been wrong before though!

C1291 is the 1291 is the 18 way white connector on the side of the BECM that is closes to the transmission tunnel, and it's the one closest to the front of the BECM"

Note that c1291 is c361 on the 1995 diagram (my year) but otherwise the same.

Anyway, I connected up my voltmeter and all worked as it should. I then swapped over a working interior light and ... NOTHING! Lots of head scratching. Must be the connector. Flaffed about with scraps of wire and electrical contact cleaner, bending pins, the works. Still no joy. Then had a bit of inspiration: pushed 2 bits of wire into the purple/red socket and the purple socket and held the wires across the bulb itself - nothing.

So, guessing I have enough voltage for DVM but not enough current to drive the bulb. Broken wire somewhere?

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Datatek said:

That is the problem with a DVM

That is the problem with a DVM, they draw no current so will read 12 volts off a bit of wet string.

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martyuk said:

Good to hear you got it fixed!

The size wire they use (I think it's 1mm2 from memory) is good for near on 16A at 12V - so running if across from the RHR light definitely won't be a problem current draw wise. The RHR light is also fed from F15 aswell - so ultimately it's coming from the same source anyway.

I am guessing you have a break in the feed wire to the LHR somewhere - though it would be tough to trace as I'm pretty sure it runs the long way down the LH sill, out and across the firewall and back in the RH side into the sill and onto the BECM. There are a few wires that come across the back of the BECM/centre console, but from memory they are all for the gearbox/transfer case

Interestingly, that wire from the BECM splices, and feeds that rear light, the LHR ICE amp in the door and the subwoofer amp (if fitted I guess). So if you have a door amp in the LHR door and the speakers are working, then chances are the break in the wire is either at the splice, or from there up the pillar into the headlining. That's more of just an FYI - running the wire across to the other light is a nice easy fix!

Marty

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