Rear left tail light problem

[robo]

Hi I am having bit of problem and I need your help, have done all forum searches and still no answer.
I have done obvious jobs like check fuse, bulbs, connector but there is no voltage coming to the plug at all, any pointers?
cheers
Rob

[UrS4boy]

Hi I am having bit of problem and I need your help, have done all forum searches and still no answer. I have done obvious jobs like check fuse, bulbs, connector but there is no voltage coming to the plug at all, any pointers? cheers
Rob

This is might not answer your question directly but it might help you investigate further. It IS intended to show that the trailer connections are in PARALLEL with the normal DOT rear lamp holder bulb filaments. It is also intended to show that corrosion in one of the metal traces could lead to a bulb out.

First of all, some basics:

a) The lamp holder is held into the taillight via a 90 deg turn "arrow head".

b) each left and right lamp holder is connected to the C4 lighting wiring harness via a four pin connector.

c) the DOT lamp holders have two, 2 filament 12V bulbs (typically a P21/5W, (5W for the running light filament and 21W for the brake light and turn signal filaments))

d) the connections to the four bulb filaments are done by stamped metal plates that mimic printed circuit boards

e) a some points there are metal traces that seem to disappear into the lamp holder, but then show up again as a contact for one of the two lamp filament contacts on the base of the bulbs

f) the ground for the bulbs is on the outside of the base of the bulbs. Pin-wise this is "31" which runs to both of the two lamp holders.

All that said, here is an annotated photo of a C4 right rear lamp holder (B4 will be similar) showing the metal traces and how any trailer light spade connections would be in parallel with the vehicle lamps and how the traces are connected (or perhaps, in your case, disconnected).

HTH

[robo]

Thanks for your reply but I had corrosion problem some time and I got pi**ed of with constant no bulb signal on the dash.
Now I have newish bulb holders with plenty of grease on the plug so no water penetration.

The issue I have that there is no power coming to the left plug at all just for the tail light, indicator and brake light is fine.

[UrS4boy]

Thanks for your reply but I had corrosion problem some time and I got pi**ed of with constant no bulb signal on the dash. Now I have newish bulb holders with plenty of grease on the plug so no water penetration. The issue I have that there is no power coming to the left plug at all just for the tail light, indicator and brake light is fine.

No power at the harness equivalent of position 3, "58"? I know you said that you checked the fuse but....(Try a new 5 Amp fuse there).

M4 Here ("e" goes to Fuse S7, as shown in the second pdf)

http://www.s2central.net/S2_Schematics/C/C01-09.pdf

http://www.s2central.net/S2_Schematics/C/C01-10.pdf

[robo]

No power at the harness equivalent of position 3, "58"? I know you said that you checked the fuse but....(Try a new 5 Amp fuse there).

I did check it and the front left side light is on.
Thanks

[UrS4boy]

I did check it and the front left side light is on. Thanks

You are correct that the front left side marker light is also supplied through the S7 fuse so the fuse is good. This means that you need to establish continuity between the output side of the S7 fuse holder and the H58L ("heck = rear, 58 = running light, L = Links = left) connector, i.e. the grey with the black stripe (gr/sw = grey/schwartz(black)) wire. This will need a multimeter set to ohms and one long lead and one short lead (the short lead in the output side of the S7 fuse holder and the long lead running down to the H58L connection point in the harness connector).

Figuring out the output side of the S7 fuse holder can be done with the fuse pulled, and the multimeter set to 20V DC and the negative lead to earth. With the ignition on and the engine running, turn the lights on. The input side of the S7 fuse holder will be the one with the 13.7V. The other side with nothing will be the output side, the one you need to check to the rear H58L connection point. Could be a break or pinch somewhere between the S7 and the H58L point.

If you knew how to do this, sorry for the suggestions above.