[Bird watcher]

Hello folks,

I am working on a 1986 911 Carrera, after a 8 year mothball. Engine rolls all instruments function except battery light.

New to this forum and following Jassbass write up titled (DME Relay explained), I am looking for some help in correcting a fault with the switched +12V coming in on pin 86 from ignition.

As is: my DME relay harness only have 12V on pin 30. Pin 86 has no power regardless of the switch position of the ignition.

What standard conditions must be first satisfied before ignition send 12V to pin 86.

Could a fault in the charging process cause the ignition not to send 12V to the DME Relay?. Reason my battery light is not coming on, and diagnosed as a faulty voltage regulator. Note: Fuel pump operates when jumped from pin 30, 87b and 87.

Any help would be appreciated.

Regards,

John

[Jazzbass]

Without +12V going to pin 86 of the DME relay, nothing is going to run. Pin 86 is fed by a black 16ga wire that can come from one of two places:

- In cars without a factory alarm, the black wire connects directly bus 15 (switched power) at the unfused side of the turn signal/back up light fuse.

- In cars with a factory alarm, pin 86 of the DME relay is controlled by the alarm unit (alarm output pin 87a). This is how the alarm stops the car from running. The alarm unit is in the trunk under the fresh air blower and is a royal PITFA to get to.

The most typical reason for no power to pin 86 of the DME relay is a malfunctioning factory alarm. If your car doesn't have an alarm, trace that black wire back to the fuse box and make sure it's connected properly. The way these fuse boxes are made is is very easy for wires to come loose.

[Bird watcher]

Chris,
Thanks for the response. I have started checking the alarm system. Here is my finding.

Probing the Alarm control module connection:

Required test: Expected results: Actual result:

* 30 & 78a Test lamp light (Test lamp did not light)
* Hn & 30 Test Lamp light (Test Lamp did not light)
E/A & 31 Alarm on 2- 3 oms (2.4 ohms)
E/A & 31 Alarm off 4 - 5.5 Oms (4.5 ohms)
MK & 30 Test Lamp on Test lamp on/ Press trunk switch off
61 & 30 Test light on Test light on (Ignition on light off)
* 15 & 31 Test light go out with Ignition on (Opposite) Light go on w/ignition
* T & 30 Open door Test lamp light Test lights did not light
31 & 30 Test lamp light Test light light on

* Indicates faults found. Still working on these- problems seem to be pointing at Ignition wiring with the opposite reading on 15 & 31. I would attempt an alarm bypass, but i hesitated giving the reverse reading on 15-31..

Thanks again.

John

[Jazzbass]

So here are the two circuits you're dealing with. First, the standard DME/DME relay power circuit. This shows the no-alarm-option connection where pin 86 of the DME relay is connected directly to bus 15 in the fuse box.



And this is the factory alarm circuit:



I didn't quite follow your results below - it looks like you posted a table of some sort but the board software removed the spacing from it. Hopefully the circuit above can be of some help. Were it me, first thing I'd do is disconnect the alarm unit from the connector and test that there is +12V on pin 15 when the ignition is turned on (in both "run" and "start"). If there is, use an alligator clip (or similar like this: http://www.amazon.com/SE-TL10-Clip-T..._bxgy_hi_img_y) to jumper from pin 15 to to pin 87a. If there is nothing else wrong with the DME relay or the DME circuit, this should get your car running. If there is NOT +12V on pin 15, jumper directly from the fuse box to pin 87a.

[Bird watcher]

Chris,
Thanks for the Diagrams. So far I found that HN jumped to 30 did not work because the alarm horn is not working. Also found a frayed wire in the wire running to 87A.
Do you have a quick point to the color coding of the wires for the Dme Relay connector.

[Jazzbass]

Originally Posted by Bird watcher

Do you have a quick point to the color coding of the wires for the Dme Relay connector.

The colors are shown in the diagram above. Follow the wires coming out of the DME relay and you'll see a number/letter combo that indicates the wire color (in German) and gauge (in mm^2). For example, the wire going from 87b of the DME relay to the fuse box is marked as "2,5RT/GN" which means it's a 2.5mm^2 wire (about 13 AWG) that is colored red (rot) with a green (grün) stripe. Metric to AWG info is here. The colors are:

RT - red
SW - black
GN - green
BL - blue
GE - yellow
WS - white
BR - brown

[Bird watcher]

Chris, Thanks for the codes. I see now the major problem I have run into is that the former owner of the 911 has rewired the vehicle and did not follow the wire color codes. He installed an after market alarm that was a bird nest of wires, and has switched wires around in the fuse box. I will try to trace each wire with a tone set, and relocate them to their factory location.. Thanks for your help I will let you know how it all turn out..
Regards
John

[Dr K]

Fixing mis-wiring after an aftermarket alarm was removed from my race car was many, many hours. Get the wiring diagram(s) and you'll get real familiar with those busses and color codes.

[Bird watcher]

Dr K. Believe me I am still a novice with car wiring diagrams, but since working on this car I actually now understands how a circuit works. It took me quite a while to understand how the little arrow was connecting the dots that allowed current to flow and not to flow. The breakthrough was to associate the wire continuing associated with the letter in the little triangle at the end of the lead to another page. Seem simple now but if you don't know you don't know..
To be able to see the working of the ignition on a wiring diagram, and understand it came in a flash, while sitting down under a coconut tree with my Bentley manual. I would dare say that I can now read a basic wiring diagram.. Not into diodes and resistors yet though.

[Bird watcher]

Hello folks, after a number of gains on rewiring the alarm on my 1986 911, all but one circuit has logic out with my test light.

The Bentley manual instructs: From the alarm module (Anti theft control switch) bridging female connector pin 15 and 31, test light should go (out) when the ignition is turned on. Instead the test light go (on) when the ignition is turned on. Following the power distribution diagram page 970-8 circuit (C) from ignition continuing to page 970-10 Circuit (C) when the ignition is turned on it seems to to power up pin 15 on the module, and most of the instrument cluster.

Could this be a type-o on the part of the manual, or am in reading the circuit wrong.

Help!!!!! John..

Fopllow-up: Pin 15 on the alarm module has continuity to pin 86 on the relay, pin 15 also has power going in to the alarm module, it seem there is no power coming out of the alarm module to power up the relay, and possibly the reason the former owner install the after market alarm. Faulty alarm module? or is it they are said to be built hard core.. Of course Chris suggested faulty alarm in his first reply. Glad I could come to the same conclusion by testing. It is a learning experience, and will worth the trip through this jungle of wires. Thanks for helping me lean and also thanks for not spoon feeding the new guy too much.