starting problem with lights on

[anggrazi]

when my light switch is in on postion my car will not start , engine does not turn , with light switch of no problem turns over , i added headlight relay, lights are much brighter but still have same problem starting could switch be bad ? switch is taped up by PO i think it gets loose with out tape ,

[aj81spider]

How new and how charged is the battery? How robust is the starting when the lights are off? It could be that the battery can't handle the load of the starter and the lights at the same time.

An easy fix is to turn the lights off before you start the car

[anggrazi]

New battery, starts fine with light off,,, just want to avoid a potential problem

[spider2081]

Have you made any voltage tests with a volt meter?
Have you tried using a battery jumper cable and jumped a ground from an engine bolt like the alternator bracket bolt on the block to a ground stud on the fender well?

[anggrazi]

ill try the ground , thanks where would i check voltage

[spider2081]

where would i check voltage

I like to start at the battery.
First measure the voltage on the battery posts Lights off. Record that measurement
Then measure the voltage at the battery posts with the lights on and compare that to the first measurement. should be within 0.5 volts if battery is fully charged.
Then make similar measurements at the battery cable terminals on the battery.
with just the head lights on the measurement between the cables should be withing 1 volt of the battery terminal measurement with lights off.
Note turning n the headlights also turns on the parking lights, side lights, dash lights and marker plate lights, In total that is a fairly large load on the battery.