W115 300D Glowplug upgrade problem
 

I installed the new glowplugs today and they do not work. I did not connect the ground to plug # 1 and i used 10 gauge wire inbetween each plug.

Im not getting any voltage to the main wire that supplies all the plugs with power.

I hear the relay clicking under the dash but i don't get any voltage to the plugs.

Stupid question #1: Did you connect the +12V wire from the firewall area to #5? How are you checking for voltage at the wire and do you know where the fuse is for the GP system on this car?

Did the system work just prior to your changeover? Did you remove all of the coil wires from between the gp's?

Yes the firewall connection is on plug # 5.

Heres what i know.

I connected plug 5 to the firewall connection only, I did NOT connect to the other 4 plugs. The light on dash came on and plug got hot.

I then connected my jumper wire to 5 but didn't connect it to 4, i had 12V. I continued with the other plugs.

If all glowplugs are connected then the light on dash doesn't come on, and NONE of the have power. If i disconnect a jump wire the light comes on and I have power to all other plugs that are connected.

Yes, the system worked fine before I touched it.

I connected 3 plugs and left the next jumper wire off and I had voltage at thatjumper. Iconnected it to plug 4 and then left the next wire that goes from 4 to 5 hanging and had NO power at all.

This makes no sense, i have tested each plug and all of them glow.

I'd try delivering 12 volts to each separate plug in turn and see if each one works separately.

I tested 3, let me go test the others.

I'd also look at the 80 amp fuse. It could have a slight crack, separating when the load of all 5 plugs are drawing current thru it.

do you know where that fuse is on a W115?

No, but on early 123's it was on the firewall in a little plastic box where the hot wire for the plugs connects.

I am trying to understand and follow your thread, You are using a jumper wires between GPs,
If it is an upgrade and you are using a glow plug timer relay, aren't you supposedly
using five wire harness to the GPs, parallel connection, not in series connection.
in any case what I understood from your post is #4 Gp shorted to ground internally,
check for continuity between wire connector to engine block.
Just my .02 cents worth.

OK. I just connected 3 plugs and they worked. I tried to connect 4 plugs and none of them worked.

Mazoot, im sure this is hard to follow. Im using the original relay, only new plugs and wires.

Kerry, Its not on thefirewall, I couldn't even find it under the dash either, its gotta be somewhere. See my post above, I think your on to something here.

OK. I'd try hooking all the plugs together, leave off the OE 12 volt delivery wire, and then run a heavy jumper wire directly from the positive post on the battery to the plugs and see if they all work. If they do, then you know the problem is upstream towards the relay.

OK i'll try that tomorrow, its dark here.

When all 5 polugs are connected I here relay click but i don't have any power to the plugs. Is the fuse after the relay?

Anyone know where the 80 amp fuse is located on the W115 body?

Fuse is after the relay on a 123, can't imagine how it could be different on a 123 since it's protecting the heavy wire going to the glowplugs and not the relay itself.