NOTE: Bonanza does not require an account. Just add the item to your cart and proceed to payment. This tiny test light is for troubleshooting Bosch L-Jetronic fuel injection as well as D-Jetronic with a slight modification to the tool. This tester is designed to help you identify the source of rough idling, stumbling, missing, etc. without expensive tools or paying a shop for labor just to narrow down the problem. You can easily narrow down the problem yourself by using the signals from this test light to rule out components. The instructions are only provided here: 1. Disconnect the harness at one injector and insert the light's two metal prongs into the end of the harness. 2. Start the car. Your EFI is now firing the test light. The engine will of course miss but the focus here is the condition of the signals going to the light. 3. If the light strobes steadily and consistently then that particular injector lead is receiving a good signal. This would indicate that the problem is the next component in the system which is the injector itself or the fuel supply to that cylinder. Try swapping out the suspect injector for a known good injector. 4. If the light flashes erratically, lights up solid, or doesn't light at all then the signal through that particular injector's wiring harness is a problem or the EFI control unit itself is failing to send the proper signal. 4a. Turn off the engine and check each wire in the injector wiring lead for continuity end to end. You could also move the harness around while the engine is running to see if the light pattern changes which would indicate a broken or shorted wire. Also check for loose/flared pin sockets. 5. If you have confirmed the integrity of the wiring harness and the connector and a known good injector does not address the issue then the EFI control unit is the final suspect. ***Tool modification required for D-Jet. The difference between L-Jet connectors and D-Jet connectors is the shape of the pins. This tool has round pins. To fit the D-Jet connector just file the pins flat. Free shipping in the U.S. SHIPPING ADDRESS: I can only send your item to the registered PayPal shipping address at time of payment.