Overview of Interfacing to the Electrical System

October 2004

Test and Make a List

Once the old engine and all of the components were removed, came the task of how to interface all the new electric drive systems to the old car? Here are the steps that were followed:

1. Apply power to the vehicle systems
2. Test as many systems as possible. Make a list of what works and what does not. This list can include:
   • turn signals, hazard lights
   • head lights, driving lights, fog lights
   • interior lights
   • windshield wipers and washers
   • heater blower and flaps
   • power windows, mirrors, door locks, hatch locks
   • Clocks
   • Freekin' car alarm
3. Test as many instruments (or warning lights) as possible. Make a list of what works and what does not. This can include:
   • parking brakes
   • high beams
   • door open, hatchback open
   • coolant, brake fluid levels
4. Make a list of instruments to interface. This can include:
   • Generator light
   • Speedometer
   • Tachometer
   • odometer
   • fuel level
   • coolant temperature
   • engine warning buzzer (e.g. on the New Beetle, it has an oil pressure warning buzzer)
5. Make a list of the instruments to disable/remove. This can include:
   • Engine check light
   • Exhaust warning light (maybe make it glow green!)
   • Oil pressure light
   • Engine Control Unit

Interfacing

• Determine the placement, connector and wires to the applicable sensor
• Determine where in the schematic diagram the sensor is located, this may help with its' characteristics
• Determine how the sensor operates (does it require power? is it magnetic? is it voltage or current limiting?)
• You will then have to figure out out to simulate or convert your signal into the signal required by the car. In some cases, the sensor from the car may be able to be used as is, and may just require specific testing.

Fixing Problems

With the list of systems/instruments which do not work, you will have to use the electrical wiring diagrams from your factory service manual to track down why it does not work.

Items to Disable/Remove

With the list of items to disable:

• If the light or instrument is already off, just ignore it.
• Check the schematic to see what kind of input the device requires.
• Try temporarily cutting power to the light or instrument, see if this works.
• Try temporarily grounding the light or instrument, see if this works.
• The input may require being pulled high (+5v) - be very careful applying power, as you may destroy your whole instrument cluster.

Cutting Away the Old

Once a scheme for interfacing the systems is tested, it is time to cut out the old wiring.

1. Mark all connectors either green (to keep) or red (to remove)
2. Strip all wire looms in the engine compartment to their bare wires.
3. In the case of the New Beetle, the ECU could not be removed (the alarm kept on triggering), so it had to stay.
4. Test the whole system again (See Electrical Testing for a list), with the following:
   • All items to be removed are removed
   • All items to be interfaced are simulated. (jumpers, signal generators, etc.)
5. If testing is not successful, figure out the problem and retest (with the New Beetle, we found out that a harness connector had to be connected for the Speedometer to work).
6. Once all tests are successful, the connectors which have been marked "red" can be cut back. Once you do this, make sure to:
   • Carefully label the wires (just in case of problems).
   • Cut the wires with enough of a lead to reconnect (if there are problems).
   • Carefully insulate, then tape the ends. (Heat shrink works well).
7. Test the whole system again (See Electrical Testing for a list), with the following:
8. Once testing is successful, tape up the wire looms and tuck neatly away.

    

   A box of electrical wires and connectors cut away from the New Beetle.