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S40-12 Volts at low beam connector but disappears when low beam is connected S40-V40

Hi Board peeps,

I have a 2000 S40 with no low beams. All the fuses are fine and each has 12 volts to ground. The bulbs were each connected directly to battery and they both work.

When I turn on headlights I read 11.5 volts at both low beam connectors. As soon as I connect the bulbs, the voltage disappears to zero. Is this called "Voltage Drop"? And is this necessarily the Central Electronics Module (CEM)?

I've read just replace the CEM but wanted to be sure.








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S40-12 Volts at low beam connector but disappears when low beam is connected S40-V40

You may have a resistance in the circuit eating up the voltage when another load is put in the circuit.

If you have a really bad connection somewhere there is no voltage going the bulbs. This could also be a bad ground.

Try using a wire to connect directly to the battery. If that doesn't work, try running a direct ground also.

If you have no luck with that, your problem is between the two wires, ie the bulbs or fixtures.

I keep a few trouble shooting wires around with various connectors on their ends - I even have some fused ones - cut the wire in half, add a female spade to each and put a new style fuse of your choice to connect them - no fuse holder needed.

I had a 740 head light that showed 12 volts and would not light - I stripped the wire, and about 8" back there was a lot of black gunk and one strand passing current - the light was actually on, but too dim to see unless it was in a dark cardboard box.
--
'96 855R,'64 PV544 driver, '67 P1800 basket case, '12 XC70, the first three are mine, heh, heh, 525,000 miles put on 10 bricks








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(Solved) S40-12 Volts at low beam connector but disappears when low beam is connected S40-V40

Thanks but the problem was the CEM relay for the left side low beam.

The CEM has a relay for each low beam. I found the wiring diagram for the CEM, turned off ignition, removed connector "F" which is the one in the middle, and shorted hot (red and yellow) #13 to #4 and to #12 in turn (the leads to the low beams). Both lights lit. This meant one of the relays was bad. I turned the lights on once more and realized only the left side was out meaning that only that relay was bad. So I hard wired #4 and #12 together as a temp fix and voila!!!, I got headlights running off of a single relay.

Drove to work in the dark, lights on, 35 minutes, and they kept working. BTW, when first I had this problem, both sides were out. I have a feeling the right side relay is also bad, but must have been jarred enough in the process to work again, at least temporarily. eBay sells the actual relays for around $32 for the pair. It looks like an easy fix if you can use a soldering gun.







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