How To Troubleshoot Porsche 944 Headlight Problems - Part A


Back in 2011 I wrote this post on how to troubleshoot a problem with the headlight lifting motor on my 1984 Porsche 944. It's now 2015 and I've had 4 trouble-free years with no headlight problems until the other day when my headlights would go up but would not retract back down. I checked the relay and the headlight fuse (Fuse 1 on the Additional Fuse Board) which were fine and then the lifting mechanism which had no obvious signs of binding so I turned my attention to troubleshooting the rest of the electronics.

For future reference anyone following my two guides on headlight problem troubleshooting should follow Part A first here (at least until the end of Step 1) then follow Part B if needed.


You will need the following:

Multimeter (capable of checking DC voltage and circuit continuity)
Flat bladed screwdriver

I also recommend that anyone reads the headlight tutorial at Clark's Garage which explains the theory of operation and has been a key guide in helping me write this post


- MOLEX Connector Test

I started by checking the voltages on the 4 pins on the headlight motor MOLEX connector (top arrow shown below)

Start by disconnecting the connector from the motor housing and then test each pin individually with a multimeter (one probe of the multimeter should be attached to a good ground on the car, the second probe is used to test each pin individually - do not short the pins otherwise you will blow the headlight fuse under the dashboard).

Before checking the voltages at the connector it should be noted that the headlight switch has 3 position states which are as follows:

Position OFF: All lights should be OFF. Headlights in the DOWN retracted position
Position ON 1: Headlights should be OFF. Parking, dash and license plate lights should be ON
Position ON 2: Dash, parking, license plate and headlights ON. Headlights in the UP raised position

The MOLEX connector is wired in the following order (shown in the picture below)

To check the voltages at the MOLEX connector you need to perform the 3 following tests and the voltages on each individual pin should be near as follows:

Grey Red/Green Brown Red/Blue
Ignition OFF
Headlight switch OFF
0v 12v 0v 12v
Ignition ON
Headlight switch OFF
0v 12v 0v 12v
Ignition ON
Headlight switch ON position 2.
12v 0v 0v 12v

If you find that all the voltages are CORRECT then the problem is likely to be the headlight motor relay, the headlight lifting motor or binding of the headlight lifting mechanism. You should then follow tutorial Part B instead.

If you find that any voltages are INCORRECT (mine failed Test 1 and was only showing 4v on the Red/Green pin) then the problem is likely to be with headlight switch, headlight fuse or wiring. You should proceed to Step 2 below.

STEP 2 - Headlight Switch Connector and Fuse Board tests

If the voltages are INCORRECT at the MOLEX connector we need to follow the problem along the wire to the next point in the connection chain using the Porsche headlight electric diagram shown below (taken from Clark's Garage tutorial).

If we start at the area around the rotary switch (this is near enough the same area as the MOLEX connector) we can see the four coloured wires labelled.

  • Grey goes to the headlight switch  - Follow Step 2a
  • Red/Green goes to the headlight switch - Follow Step 2a
  • Red/Blue goes to the fuse board (Fuse 1 on the Additional Fuse Board) - Follow Step 2b
  • Brown goes to ground (bottom right) - You should do a continuity test between the pin on MOLEX connector and the ground point underneath the right front headlight, regardless you should unbolt and clean the ground point

STEP 2a - For the back of the headlight switch connector (Red/Green and Grey wires only)

Use a flat bladed screwdriver to pop the plastic headlight switch housing and remove it from the dashboard. Keep the headlight switch connected to the connector block and perform Test's 1, 2 & 3 on the back of the headlight switch connector for the Red/Green and Grey wires only (shown in the bunch below)

CORRECT voltages for the Red/Green or Grey wires indicate that the issue is likely the Red/Green or Grey wire itself (broken, shorting or poorly crimped at the connection points at either end), therefore the wire needs to be fixed or changed. In my case I was seeing 12v on the Red/Green wire on the back of the headlight switch connector, therefore my problem was the Red/Green wire itself as it was only 4v at the MOLEX end. There was no problem with the crimping at either end so I cut the wire at both ends and patched in a new length as it was too difficult to find a short or break. My headlights now retracted correctly.

INCORRECT voltages for the Red/Green or Grey wires indicate that the problem is likely a headlight switch fault or a problem with the main power wire to the switch. Therefore you need to do a switch continuity test (see Step 3) or a voltage test to the headlight switch connector block (see Step 4).

STEP 2b - For the fuse board (Red/Blue wire only)

Locate the 'Additional Fuse Board' underneath the dash (shown below), then locate Fuse 1 (16A) shown below.

There are two screws that hold the entire fuse board bracket to the underside of the dash, undo these so you can gain access to the back of Fuse 1. On the back of Fuse 1 you will see a Red/Blue wire and Red wire. 

CORRECT voltage for the Red/Blue wire indicates that the issue is the Red/Blue wire itself (broken, shorting or poorly crimped at the connection points at either end)

INCORRECT voltage for the Red/Blue wire indicates that the issue is a faulty fuse or that the fuse board is not receiving enough power. Recommend to replace 16A fuse and check Red wire on Fuse 1 is showing 12v

STEP 3 - Headlight Switch Continuity Test

This is what the inside of a brand new headlight switch looks like on a 944/1. The left-hand-side shows the dimmer variable resistor and the contact plates that connect to the various blade connectors on the back of the switch. The right-hand-side shows the 3 sprung switch plates that are activated/deactivated at the various 3 positions when the switch is cycled.

Here's what the inside of my used headlight switch looked like. The switch still functioned correctly but there was definitely signs of wear on the contact plates, so I replaced it just as a matter of caution.

To test the proper functioning of the switch remove the switch from car and do a continuity test using the various connector blades on the back (as shown below).

Using the below diagram you should get continuity at the red and green groups of points when the switch is in the various OFF and ON positions. If you fail to get these results you may be able to disassemble the switch and clean the contact points inside to get it working correctly. If all fails you will need to buy a new switch.

You can also test the resistance range between the 2 pins 58a and 59b for the dimmer. My new switch showed a range of between 0.5 to 7.0 ohms (Ω).

STEP 4 - Headlight Switch Connector Block Voltage Test

Testing the front of the headlight switch connector block is straight-forward and the correct voltages should be present using the table below.

Ignition OFF Ignition ON
X 0v 12v
56 0v 0v
58L 0v 0v
56K 0v 0v
58 0v 0v
30b 0v 0v
58R 0v 0v
30 12v 12v
58a 0v 0v
58b 0v 0v

Whilst the switch is detached from the block this is also a good opportunity to replace the bulb that illuminates the headlight switch. Bulb specs are as follows and can be found on ebay.

Osram 286 Single Bulb 12V 1.2W Dashboard Dash Interior Auxillary Car Single
Product Dimensions (mm): H 18 x W 5 x D 5
12v 1.2w W2 x 4.6d Indicator & Panel

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