Volvo: 1987 240 DL starter issue, ground wires, battery tester

Question
My 1987 240DL starter will not engage. When I turn the iginition switch the headlights and radio turn off and the starter will not engage.  How do I go about diagnosing the problem? The starter will bump over when using a bump start switch.
Thanks for you help.  

Answer
Tom,
Do the basic tests, use a battery tester and make sure the battery has power. Inspect the wires to the starter from the battery making sure they are good and tight. Be sure that all ground wires are connected and clean. See how many volts are delievered to the starter when the key is turned. That is to the small wire on the starter. (The large one should always have 12 volts). Anything less than 10.5 volts is not enough to engage the starter. If when you turn the key no voltage is going to the starter, see if it is in park and if it is, test the neutral safty switch, making sure that it is adjusted right, and that power is flowing through it when the key is turned. If all that checks out you may have a bad starter or switch. Remove the starter using a battery charger see if the starter will operate on it's own. If you are not getting 12 volts to the small wire with the key turned (only 8 to 10 volts), you may have to much resistance in the wiring. There is a relay kit that can be installed to help that problem.