mounting external relays for headlights

By MikeT in How-To: 450 Model, 2005-2006, diesel,
As you may know, last week my smart Canada 1 had what I thought was a burnt out right headlight. I changed the bulb the next day and....hmmmm...still out. Checked fuse 22, nope, it's fine. Conclusion: SAM failure in that circuit or maybe a melted connector, or both. The good news is that the left headlight was still working. So my plan was to use the one "good" headlight circuit to run both of them, if the right headlight circuit in the SAM was dead. I pulled the SAM down (two T-10 screws hold it in) and pulled out the N11-3 plug. It was melted on the two central pins (as well as the one that runs the fuel pump, which was previous damage). The SAM also showed heat damage on the two central pins: My SAM had been replaced at my cost in 2013, 26 months ago in fact, but the parts warranty was up and that's that. The dealer in Victoria, Three Point Motors, kindly offered me a free repair harness for the N11-3 plug (usual cost is about $60). I had some Hella 30A relays and bought some shrink wrap, an inline 30A fused link and some corrugated wiring sheathing in the smallest available diameter. The work was done Saturday. The first thing to do is to undo the plastic rivet holding the felt under dash panel in place, which makes the wiring job easier. The repair harness had an identical plug (brown) to the one seen two photos above with the melting damage, but the wires were all different colours and in different positions. Plus there was an extra wire. So splicing this into the car's harness was not only unnecessary, it would have been impossible using the pigtails that came with the repair harness. The thing to do was to remove all wires from the repair harness plug and then insert the ones on my car. So I did. The was the first step in diagnosing whether the right headlight circuit within the SAM was actually dead or not. The wiring connectors are freed from the brown plastic plug by gently prying up the side cover plate on one side of the plug, which is a secondary method of retaining the connectors within it, and then gently lifting the little brown plastic barbs that hold the pins in near the end. I took one out at a time, of course being careful to insert the removed plug into the same position on the replacement brown plastic connector. After this was done and the plug's side cover was snapped down again, it was reinserted into the SAM and I tried it out. The right headlight still did not work. But was it the SAM or the connector in the plug? I then unclipped the dead wire and cut it off about 6 cm above the connector. I then got a new connector that I had removed from the harness, cut it and soldered it inline. Reinserted into the plug and - it worked! So the SAM is not grievously damaged! I did the same to the "good" connector for the left headlight, in case it had some residual damage as well. The plan, now that I knew both headlight circuits were OK, was to run a single 12 gauge wire from the positive battery terminal to the vicinity of the SAM, where it would be soldered to a 30A inline fuse holder (I used a 25A fuse, which is probably still too large!) , then it would branch into two in order to provide the external supply to run the lights. I would mount two 30A relays next to each other near the SAM, one for each headlight (overkill, but redundancy is good). The 12 gauge supply wire from the battery was inserted inside a metre long corrugated plastic sheath (to prevent chafing) and threaded through to the driver's side using the space just behind the "firewall". It was zap strapped to the hot terminal on the battery to ensure it stays in place. A "Y" piece of wire was fabricated for the relay grounds and I secured both relays to a piece of drilled metal strapping. The next task was to take the power leads from the SAM and splice in a connection for each relay. For this purpose I used the removed wires from the new N11-3 harness, so they matched the colours of the originals. It was simply a question of soldering the new wires inline with the cut I made in the old ones (about 15 cm back from the connector) and soldering a connector onto the end for the relay. Then the lead from the relay to headlights had to also be spliced into the original wires. You will notice that I made insulating sheaths for each connector, you can never be too careful! Once that was done, the metal strap the relays were attached to was bolted to the large ground bolt above the dead pedal. Make sure that the grounds that were there are attached when you bolt it down (if you use the same technique as I did to secure the relays), as well as the Y-wire used to ground the relays. And that was it, the SAM was bolted back into place, the felt under dash panel was clipped back into place using the plastic rivet. A test showed all is well.
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